Effect of supplemental lighting on primary gas exchanges of

Chrysanthemum × morifolium Ramat cultivar White Reagan

By Xiao Ma

A Thesis

Presented to

University of Guelph

In partial fulfillment of requirements

for the degree of

Master of Science

in

Plant Agriculture

Guelph, Ontario, Canada

© Xiao Ma, October 2017

ABSTRACT

Effect of supplemental lighting on primary gas exchanges of

Chrysanthemums × morifolium Ramat cultivar White Reagan

Xiao Ma Advisor:

University of Guelph, 2017 Professor Bernard Grodzinski

Flower greenhouse production is reduced in winter, which is due to the short

photoperiod and low light levels. Studies indicate that LEDs could increase the quality and

yield of ornamental crops. However, there is very little research about LED and HPS effects

on chrysanthemums during long day (LD) and short day (SD). Plants were grown in the

research greenhouse and growth chambers at the University of Guelph. Plants were

subjected to a 16h photoperiod (LD) and a subsequent 12h photoperiod (SD). Four different

light treatments were compared: 1) Natural light (Amb), 2) Amb supplemented with

Red/white LEDs, 3) Amb supplemented with Red/blue LEDs and 4) Amb supplemented

with HPS. Plant height, leaf area, dry matter of different parts, SPAD reading, and leaf and

whole-plant level photosynthesis, respiration, transpiration, water use efficiency and daily

carbon gain during both long day and short day periods were measured. We concluded that

chrysanthemums showed different response to light spectrum quality between LD and SD

at the leaf level but not the whole plant level.

iii

Acknowledgements

I would first like to sincerely thank my thesis advisor Professor Bernard

Grodzinski, who is not only teach me in my master program but also help me a lot during

my foreign life. The door to Prof. Bernard office was always open whenever I ran into a

trouble spot or had a question about my research or writing. He consistently allowed this

paper to be my own work, but steered me in the right the direction whenever he thought I

needed it. I would also to thank my committee member: Professor Michael Dixon and

Professor Barry J. Micallef for their passionate participation and help which helped me to

improve my thesis and experiment design.

I would like to thank Dr. Evangelos Demosthenes Leonardos for his friendship and

help with the technical aspects during experimental set up and data analysis. Naheed Rana

for her technical support in the as well as Ron Dutton and David Kerec for their assistance

with LED lighting and growth chambers.

Finally, I am grateful to my fellow graduate students, Jason Lanoue and Jonathan

Stemeroff, for their friendship and advice throughout my masters. I also want to thank

Theo Slaman for his supporting. I must express my very profound gratitude to my parents

and my friends in both Canada and China for providing me with unfailing support and

continuous encouragement throughout my years of study and through the process of

researching and writing this thesis. This accomplishment would not have been possible

without them.

iv

Table of contents

ABSTRACT .................................................................................................................................... ii

Acknowledgements ........................................................................................................................ iii

Table of contents ............................................................................................................................ iv

List of Figures ................................................................................................................................ vi

List of Tables ................................................................................................................................ viii

List of Abbreviations and Definitions .......................................................................................... ix

1. Introduction ............................................................................................................................... 1

2. Literature Review ...................................................................................................................... 3

3. Materials and Methods ............................................................................................................. 6

3.1 Plant materials and growth conditions .............................................................................. 6

3.1.1 Research greenhouse chrysanthemums ...................................................................... 6

3.1.2 Growth chamber chrysanthemums ............................................................................ 6

3.1.3 Burford commercial greenhouse chrysanthemums ................................................... 7

3.2 Measurements ...................................................................................................................... 7

3.2.1 Leaf gas exchange measurement ................................................................................. 9

3.2.1.1 Research greenhouse chrysanthemums leaf gas exchange .............................. 12

3.2.1.2 Growth Chamber chrysanthemums leaf gas exchange .................................... 12

3.2.2 Whole plants gas exchange measurement ................................................................ 12

3.2.2.1 Research greenhouse chrysanthemums whole plants gas exchange ............... 17

3.2.2.2 Growth Chamber chrysanthemums whole plants gas exchange ..................... 17

4. Results....................................................................................................................................... 18

4.1 Research greenhouse chrysanthemums ........................................................................... 18

4.1.1 Chrysanthemums growth and development in research greenhouse .................... 18

4.1.2 Chrysanthemum whole plant gas exchange of research greenhouse grown plants

............................................................................................................................................... 23

4.1.3 Chrysanthemum leaf gas exchange of research greenhouse grown plants ........... 42

4.2 Growth chamber chrysanthemums ................................................................................. 51

4.2.1 Chrysanthemums whole plant gas exchange in growth chamber .......................... 51

4.2.2 Chrysanthemums leaf gas exchange in growth chamber ........................................ 61

v

5. Discussion ................................................................................................................................. 66

5.1 Whole plant diurnal patterns of gas exchange and growth during LD and SD .......... 66

5.1.1 LD and SD under conventional HPS ........................................................................ 66

5.1.2 LD and SD under newer LED systems ..................................................................... 67

5.2 Leaf gas exchange during LD and SD ............................................................................. 69

5.3 Summary and implications ............................................................................................... 69

Reference ...................................................................................................................................... 72

Appendix ...................................................................................................................................... 77

vi

List of Figures

Figure 3.1: Light spectrum of W, R, B, RB, RW and HPS used in leaf gas exchange

measurement …...…………………………………………………………………………………10

Figure 3.2: Examples of leaf gas exchange measurements ……………………………………….11

Figure 3.3: Light spectrum of HPS, RB and RW LED used in the whole plant gas exchange

system ….........................................................................................................................................15

Figure 3.4: Overview of whole plant gas exchange system …………………………………..…..16

Figure 4.1: Height of chrysanthemums grown in the research greenhouse ……………….………19

Figure 4.2: SPAD reading of chrysanthemums grown in the research greenhouse ……….……...20

Figure 4.3: Leaf area and open flower number of chrysanthemums grown in the research

greenhouse at final harvest …………………………………………………………….………….21

Figure 4.4: Dry weight of different parts of chrysanthemums grown in the research greenhouse at

final harvest …………………………………………………………….………………………...22

Figure 4.5: Hourly whole plant net carbon exchange rate, transpiration rate and water use

efficiency of non-acclimated and acclimated plants grown in the research greenhouse during

LD ………………………………………………………………………………………...………26

Figure 4.6: Daytime and nighttime average whole plant NCER of non-acclimated and acclimated

plants grown in the research greenhouse during LD ……………………………..……….……….27

Figure 4.7: Daily whole plant carbon gain of non-acclimated and acclimated plants grown in the

research greenhouse during LD …………………………………………………..………………29

Figure 4.8: Average whole plant transpiration and WUE of non-acclimated and acclimated plants

grown in the research greenhouse during LD.…………………………………….…………...…. 31

Figure 4.9: Hourly whole plant NCER, transpiration and WUE of acclimated plants grown in the

research greenhouse during LD and SD ………………….………………..………….…………..34

Figure 4.10: Daytime and nighttime average whole plant NCER of acclimated plants grown in the

research greenhouse during LD and SD ………………………..………………………..………..35

vii

Figure 4.11: Daily whole plant carbon gain of acclimated plants grown in the research greenhouse

during LD and SD ……………….………………………………………………………….…….37

Figure 4.12: Average whole plant transpiration and WUE of acclimated plants grown in the

research greenhouse during LD and SD ……………...…………………………………………...39

Figure 4.13: Light curves for leaf NCER, transpiration and WUE of research greenhouse grown

chrysanthemums during LD under the different supplemental lights …………………..…………43

Figure 4.14: Leaf NCER light response curves of research greenhouse grown chrysanthemums

during LD under different supplemental light sources ……………………………………………45

Figure 4.15: Light curves for leaf NCER, transpiration and WUE of research greenhouse grown

chrysanthemums during LD and SD ……………………………….…………...……….………..48

Figure 4.16: Leaf NCER light response curves of research greenhouse grown chrysanthemums

during LD and SD ……………………………………………………………………….………..49

Figure 4.17: Hourly whole plant NCER, transpiration and WUE of plants grown in the growth

chamber during LD and SD ………………………………………………………………………53

Figure 4.18: Daytime and nighttime average NCER of plants grown in the growth chamber during

LD and SD ………………………………………………………………………………………..54

Figure 4.19: Carbon gain of plants grown in the growth chamber during LD and SD ……………56

Figure 4.20: Average transpiration and WUE of plants grown in the growth chamber during LD

and SD …………………………………………………………………………..……………......58

Figure 4.21: Light curves for leaf NCER, transpiration and WUE of growth chamber grown

chrysanthemums during LD and SD ……………………………………………………………...62

Figure 4.22: Leaf NCER light response curves of growth chamber grown chrysanthemums during

LD and SD under different light sources ………………………………………………………….63

Appendix Figure 1: Commercial greenhouse chrysanthemums vs Research greenhouse

chrysanthemums final height ……………………………………………………………………..76

Appendix Figure 2: Commercial greenhouse chrysanthemums vs Research greenhouse

chrysanthemums final SPAD reading ………………………………………………...…………..78

viii

List of Tables

Table 3.1: Time line for leaf and whole plant gas exchange measurements for growth chamber and

research greenhouse chrysanthemums. ……………………………..…………….………………..8

Table 4.1: Whole plant leaf area, dry weight and specific leaf weight of research greenhouse plants

used for whole plant gas exchange measurements during LD and SD…...….…….………………41

Table 4.2: A summary of the major physiological traits determined by analysis of leaf gas

exchanges of research greenhouse chrysanthemums during LD ……………………….…………46

Table 4.3: A summary of the major physiological traits determined by analysis of leaf gas

exchanges of research greenhouse grown chrysanthemums during LD and SD ………..…………50

Table 4.4: Leaf area, dry weight and specific leaf weight of growth chamber plants used for whole

plant gas exchange measurements during LD and SD ……………………………..……………...60

Table 4.5: A summary of the major physiological traits determined by analysis of leaf gas

exchanges of growth chamber chrysanthemums during LD and SD ……………………….……..64

ix

List of Abbreviations and Definitions

Amb: Ambient condition (no supplemental light)

B: Blue LED

DW: Dry weight (g)

HID: High-intensity discharge

HPS: High pressure sodium

LA: Leaf area (m2)

LCP: Light compensation point. The light intensity level when the plant photosynthetic rate is

equal to the respiration rate so that the NCER is equal to 0.

LD: Long day period

LED: Light-emitting diode

NCER: Net carbon exchange rate (μmol m-2 s-1)

PAR: Photosynthetically active radiation

Pn: Photosynthetic rate (μmol m-2 s-1)

PPFD: The photosynthetic photon flux density (μmol photon m-2 s-1)

R: Red LED

RB: Red-blue LED

Rd: Respiration rate (μmol m-2 s-1)

RW: Red-white LED

SD: Short day period

SLW: Specific leaf weight, dry weight per leaf area (g m-2)

W: White LED

WUE: Water use efficiency, the rate of Pn to E (μmol CO2 mmol-1 H2O)

x

YQ: Maximum quantum yield. An estimate of the maximum slope given by the nonlinear

equation. CO2 fixed per photon absorbed under PPFD limited condition.

1

1. Introduction

Greenhouse production is one of the biggest industries in Canada. Not only various

vegetables are grown year-round, but also many varieties of flower crops are grown commercially

in greenhouses. From the data of Statistic Canada of 2015(Statistical Overview of the Canadian

Ornamental Industry-2015), the area of greenhouse flower production was approximately 7.8

million square meters and the sales of the ornamental greenhouse products was approximately

$2.02 billion, which increased from $1.93 billion in 2014. Ontario is still the largest province of

greenhouse flowers and plants, taking a 44% share of the total production area, followed by British

Columbia (25%) and Quebec (16%).

Indoor production could provide the optimum environment, where the temperature,

humidity and CO2 level are suitable for plants to grow. In the greenhouse production, there are

many factors that are related to yield, such as plant density, temperature, CO2 concentration,

humidity and light conditions. Supplemental lighting systems are usually used in the greenhouse to

provide extra light intensity not only during no-sunshine weather but also low light seasons (fall

and winter). Because of the huge effect on final yield, farmers need to consider about the light

system very carefully and spend a lot of money on it, when they are preparing to build a greenhouse.

In accordance to that, it is valuable for us to consider many aspects of a lighting system and

especially light quality.

There are many types of lamps which have been used in lighting systems for growing plants.

The most commonly used light sources include fluorescent, high intensity discharge and

incandescent lamps. For example, fluorescent lights are often used over germination shelves

because they can be placed close to plants without overheating them. But they are usually not used

for supplemental lighting in the greenhouse as their fixture causes excessive shading. High intensity

discharge (HID) lamps are most often used for greenhouse supplemental light because of their high

light output and relatively little shading – there are two main types: high pressure sodium (HPS)

which look yellow/orange and metal halide which look bluish. All these lamps were originally

designed for human lighting application. Since humans have different photoreceptors from plants,

these light sources have various limitations and are not very optimum for growing plants. For

instance, HPS was introduced around 1970 and have been used as the main technology. The

advantages of HPS include long lifetime and relatively moderate installation cost (Van Ieperen and

Trouwborst, 2007). However, HPS lamps still have shortcomings. It is a wide range spectrum lamp

that cannot provide the specific narrow wavelength lighting, which is more significant for plant

2

photosynthesis. To solve this problem, a new type of lighting system is introducing, light emitting

diodes (LEDs).

LEDs are semiconductor devices that produce narrow-spectrum light. The wavelength of

LEDs can be from the UVC band (250nm) to infrared (1000nm). The type of semiconductor

material determines the color of the light emitted. The commonly cited advantages of LEDs are

efficiency and lifetime. LEDs are more efficient (radiation output divided by electric input) than

fluorescent and incandescent lamps and are roughly equivalent to the newest HPS lamps (Fig.1

Bourget, 2008). The lifetime of LEDs is two to three times better than HPS or fluorescent lamps

(Fig.2 Bourget, 2008). Although the cost for setting up the LEDs is larger than that of conventional

lighting system such as HPS, LEDs are becoming more affordable and of higher output with the

development of light technology in recent years. In addition, the most attractive aspect of LEDs in

the plant growth field is that LEDs could provide specific narrow spectrum and are often red and

blue to target spectra where photosynthesis is slightly more efficient. Considering this advantage,

LEDs are thought as an alternative lighting system replacing the conventional ones, such as HPS.

In my experiments, I suppose to compare HPS, which is commonly used in the greenhouse industry,

and LED, which is believed to be the future of greenhouse lighting system, in ornamental

greenhouse production-chrysanthemum.

Chrysanthemum is a major cutting flower produced in Canada. In 2015, there were 3.9

million cutting chrysanthemums being sold, taking the fourth position of flower production

(Statistical Overview of the Canadian Ornamental Industry-2015). The production of

chrysanthemums is variable depending on the cultivar, but common procedures are as bellow:

Cuttings are taken from the stock plants when it is optimal. The cuttings should be planted on a

misting bed (in the well-watered soil and then irrigated with a liquid fertilizer) to root. Long day

photoperiod (LD; 16h day/8h night) should be applied to them from the first day. After one or two

weeks, the rooted cuttings are transplanted into the ground in the greenhouse and stay in the long

day period. Three weeks later, when chrysanthemums have reached the desired stem length (around

35-50cm), the photoperiod is changed to the short day (SD; 12h day/12h night), which will induce

flowering. Black curtains are usually used to cover the plants and ensure the SD conditions. It

normally requests five or more weeks to develop flowers and harvest the crop.

3

2. Literature Review

With the development of lighting technologies, LEDs have been proved as a new source

for supplemental lighting in both research and commercial purposes (Nakamura et al., 1994;

Tepperman et al., 2004). Comparing with the conventional HPS, LEDs have the several

characteristics: (i) be able to provide specific wavelength lighting, (ii) a cooler light emitting

surface, (iii) be able to use internal of the canopy (Nakamura et al., 1994; Nelson and Bugbee,

2014). For commercial usage of LEDs, it is important to understand how plant production can be

optimized by receiving both natural and LED lighting at the different seasons of the year (Runkle

and Heins, 2001; Kim et al., 2004b; Gomez and Mitchell, 2015; Rabara et al., 2017).

Most of the studies of LED and photosynthesis are based on leaf gas exchange (Goins et

al., 1997; Kim et al., 2004a; Hogewoning et al., 2010; Liu et al., 2012). Leaf physiological traits

have been studied as a representative of whole plant functions under different environment

conditions (Liu et al., 2009). However, it is well known that the physiology of a single organ such

as a leaf differs from the traits exhibited at the whole plant level because of mutual shading,

different ages of leaves and canopy architecture (Davis and McCree, 1978; De Vries, 1982; Dutton

et al., 1988). Totally saying, whole plant gas exchange cannot be simply predicted by leaf gas

exchange data. Whole plant gas exchange data also can be used to show the daily growth patterns

of the plant exposed to different physiological conditions (Dutton et al., 1988; Leonardos et al.,

2014).

Specific wavelength LEDs have been used to study chrysanthemum growth and

development. For example, one study illustrated that light quality affected the flowering inhibition

of Chrysanthemum morifolium when light was used during the night break, because of the

phytochrome responses in the flowering response (Higuchi et al., 2012). Also, light quality could

affect micro propagation of chrysanthemum (Dendranthema grandiflora cv. Tzvelev). Green light

increased length of stem, internodes and fresh weight. Blue (B) light produced the shortest stems.

Red (R), green and white light affected the root system of chrysanthemum (Miler and Zalewska,

2004). Shimizu et al. (2005) compared the effect of blue light and fluorescent lamp on

chrysanthemums (Dendranthema × grandiflorum cv. Reagan) height. The results showed that blue

light could be used to inhibit the stem elongation. One experiment showed the red LED (663nm)

was related to chrysanthemums floral bud differentiation (Fukui et al., 2009). Some Chinese

researcher found the usage of LED for growth of chrysanthemum (Dendranthema morifolium cv.

Tzvel.) plantlets in vitro. They claimed that red LEDs effected height and the synthesis of soluble

4

sugar, while the chlorophyll content was significant increased by blue light (Huan et al., 2010).

One previous study discovered that the quality of LED light affected not only the flowering but

also the leaf polyphenol production of Chrysanthemum morifolium (Jeong et al., 2012). In a

separate experiment, they indicated that blue LED could increase the stem elongation, without the

inhibition of flower bud formation (Jeong et al., 2014). Far-red light reduced the growth processes

of Chrysanthemum morifolium Ramat. ‘Ellen’ in vitro but promoted the growth of root length. Far-

red light could decrease the content of chlorophyll as well. Thus, the chrysanthemum growth

processes were able to be controlled by far-red light (Kurilčik et al., 2011). On the other hand, some

researchers focused on the light combination comparison. One study showed the comparison of

fluorescent light vs different LED lights in chrysanthemum (Dendranthema grandiflorum Kitam

‘Cheonsu’), in terms of net photosynthetic rate, fresh/dry weight, leaf area and the size and number

of leaf stomata (Kim et al., 2004). Moreover, combination of different lights was also involved with

chrysanthemum (Chrysanthemum morifolium Ramat. ‘Coral Charm’) growth. Low red to far-red

ratio light could promote the height of plants, while it did not affect the stem diameter, dry matter

and internodes number (Lund et al., 2007).

Interestingly, there is surprisingly little research about light quality and effects on

photosynthesis and virtually no data on transpiration or water use efficiency (WUE). One Chinese

team (Zhou et al., 2013) found that maximum net photosynthetic rate, light compensation point and

light saturation point were different among chrysanthemum cultivars, but this study was not about

spectral quality but an analysis of leaf photosynthesis of different cultivars. At the whole plant level,

there appears to be no data regarding photosynthesis or water gas exchange for chrysanthemums.

Recently, however our group reported the effects of LEDs on two other crop plants, lisianthus, and

ornamental cut flower, and tomato (Lanoue et al., 2017). Our results indicated that at the whole

plants level, plants grown under red-blue and red-white LEDs had lower WUE than those irradiated

with HPS. The net biomass gain and the daily carbon budget under HPS and LED systems were

similar. These studies have lead me to my own experiments on chrysanthemums, a SD commercial

greenhouse crop.

My two, working hypotheses are a) use of selected LEDs (i.e., Red-blue and Red-white) as

the supplemental lights will produce chrysanthemum cut flowers of similar commercial quality and

at the same rate as those grown traditionally under HPS, and b) the two selected LEDs (i.e., Red-

blue and Red-white) supplemental lights can replace conventional HPS lighting that provides

photosynthetically active radiation during both LD and SD production cycle. To our knowledge,

little is known regarding photosynthesis, growth and morphology, specifically comparing LD and

5

SD as influenced by HPS. To date no information is available regarding the newer, electrically

more efficient LED lights that would be deployed to supplement natural solar radiation during fall

and winter in Canada. In summary, the primary objective of my studies was to provide fundamental

physiological data regarding whole plant and leaf responses of chrysanthemums during LD

(vegetative) and SD (flowering) stages to supplemental HPS and LED systems.

6

3. Materials and Methods

3.1 Plant materials and growth conditions

3.1.1 Research greenhouse chrysanthemums

The chrysanthemum cultivar (White Reagan) was grown in the Bovey greenhouse in the

winter of 2017. Rooted cuttings were transplanted from plug trays to 14cm diameter pots after

getting them from the supporting grower’s greenhouse (Slaman’s Quality Flowers, Burford,

Ontario, Canada). Sungro professional growing mix #1 (Soba Beach, AB, Canada) was used as

medium, which contains Canadian sphagnum peat moss, coarse perlite and dolomitic limestone.

All the pots were put on 4 benches based on a complete randomized block design in the Bovey

research greenhouse. Four lighting treatments were set during the experiment, HPS, Red-blue (RB)

LED, Red-white (RW) LED and ambient (Amb, no supplemental lighting). Considering about the

irradiance obtain with HPS lamp in supporting grower’s greenhouse, the light intensity of three

supplemental lights above was set at 100±25 μmol m-2 s-1, Photosynthetic active radiation(PAR).

The LEDs we used were 390W fixtures, provided by The Light Science Group Corporation (LSGC;

Warwick, RI, USA) and the HPS lighting were a 400W HPS lights from Philips (Markham, ON,

Canada).

This research greenhouse experiment was a light-acclimation experiment: all the

chrysanthemums were grown under the supplemental light during their whole life cycle, not just

exposed to the different light for a short period. The growing conditions were controlled by

greenhouse control program. The temperature was 20±2oC. Watering was manual with a fertilizer

solution (20-8-20) and was done 3 times per week. The photoperiod was set as 16 hours/8 hours

(day/night) for long day (LD) period and 12 hours/12 hours for short day (SD) period. Plants were

kept growing in LD period for 3 weeks and then changed into SD period.

3.1.2 Growth chamber chrysanthemums

Rooted cuttings of chrysanthemum (White Reagan) was transplanted from plug tray to

10cm diameters pots in both summer and fall of 2016 and the winter of 2017. The plant material

was provided by Slaman’s Quality Flowers (Burford, Ontario, Canada). Sungro professional

growing mix #1 (Soba Beach, AB, Canada) was used as medium, which contains Canadian

sphagnum peat moss, coarse perlite and dolomitic limestone. All the pots were placed into the

growth chamber (GC-20 Bigfoot series, Biochambers, Winnipeg, MB, Canada) in the Bovey

building at the University of Guelph. The growing conditions were controlled by the chamber

7

control program. The daytime temperature was 22oC and the nighttime temperature was 19oC. The

humidity was constantly 70%. Watering was manual with a fertilizer solution (20-8-20) and was

done 3 times per week. The fluorescent tubes and incandescent bulbs were set as the light source

in the growth chamber and the light intensity was 300±50 μmol m-2 s-1 PAR at the top of the plants.

The photoperiod was set as 16 hours/8 hours for LD period and 12 hours/12 hours for SD period.

The chrysanthemums were grown under LD period for 3 weeks then changed into SD period.

3.1.3 Burford commercial greenhouse chrysanthemums

The same cultivar of chrysanthemums (White Reagan) was planted into ground on Feb 23rd

of 2017 in a commercial greenhouse in Burford (Slaman’s Quality Flowers). The temperature was

20±2℃. And the humidity was set at 75±5%. The same four light sources as my description in

research greenhouse, HPS, RB, RW and Amb, were set above the different rows in the greenhouse.

The light intensity of all the supplemental lights was 100±25 μmol m-2 s-1 PAR at the top of the

plants. The photoperiod was set as 16 hours/8 hours for LD period and 12 hours/12 hours for SD

period. The photoperiod was changed to SD on March 9th.

3.2 Measurements

Plants height and SPAD reading measurement were taken every week in the research

greenhouse during the whole experiment. After 2 weeks of growing during LD, both growth

chamber and research greenhouse chrysanthemums began to be tested by a leaf (Licor6400) and a

whole plant gas exchange system. After 1 week of growing under SD, both growth chamber and

research greenhouse chrysanthemums began to be tested by the leaf (Licor6400) and the whole

plant gas exchange system. The leaf area was measured by a leaf area meter (LI-3100, LI-COR,

Lincoln, NE, USA) after plants were taken out from the whole plants gas exchange system. The

leaves, stems and clean-washed roots were collected separately and put into an oven at 70oC for

48h to get the dry weight of different parts. The research greenhouse chrysanthemums provided the

final harvest data, which included final height, SPAD reading and open flower number.

8

Table 3.1: Time line for leaf and whole plant gas exchange measurements for growth chamber and

research greenhouse chrysanthemums. “Week” means the week after transplanting.

Growth chamber chrysanthemums

photoperiod LD SD

week 1 2 3 4 5 6 7

measurement

WPS

WPS

leaf

study leaf study

Research greenhouse chrysanthemums

photoperiod LD SD

week 1 2 3 4 5 6 7 8 9 10

measurement

WPS

WPS

leaf

study leaf study

9

3.2.1 Leaf gas exchange measurement

For the leaf gas exchange measurements, we used the Licor 6400 portable unit (Lincoln,

NE, USA) with the different light sources. Well-watered plants were randomly selected and the 5th

highest, most expanded leaf was used for analysis. The leaf was put into the leaf chamber of a Licor

6400 portable unit (Lincoln, NE, USA). The relative humidity was set steady at 70±5% by the

desiccant. The concentration of CO2 was held at 420±10 μmol mol-1 by Soda Lime. The light I used

were the same to that in the lisianthus paper (Lanoue et al., 2017). The spectrum of the different

light was showed in Figure 3.1.

10

Figure 3.1: Light spectrum of W, R, B, RB, RW and HPS used in leaf gas exchange measurement.

The data comes from the previous work on tomato and lisianthus (Lanoue et al., 2017).

Wavelength (nm)

400 500 600 700

Sp

ectr

al C

om

po

sitio

n (

%)

0

20

40

60

80

100

Red-Blue

Red-White

White

Red

Blue

HPS

11

Figure 3.2: Examples of leaf gas exchange measurements. Leaf gas exchange measurements under

the Licor 6400 RB LED light source (A) and leaf gas exchange measurements under the different

LEDs (e.g., RB) (B).

12

3.2.1.1 Research greenhouse chrysanthemums leaf gas exchange

Research greenhouse chrysanthemums leaf CO2 and H2O gas exchange measurements

began from the third week of LD period and the second week of SD period. The leaf was put into

the leaf chamber of a Li-COR 6400 portable unit (Lincoln, NE, USA) with a RB light source from

Li-COR or different external LED light sources. Light curves using the Licor RB light source were

produced by using the Licor 6400 auto curve feature starting from a high light intensity and

decreasing step by step down to no light. Light curves using the different external light source (LED

lamb and HPS) were produced by using the Licor 6400 but changing the light intensity manually,

from a high intensity to no light.

3.2.1.2 Growth Chamber chrysanthemums leaf gas exchange

Growth chamber chrysanthemums leaf CO2 and H2O gas exchange measurement began

from the third week of LD period and the second week of SD period. The leaf was put into the head

chamber of a Li-COR 6400 portable unit (Lincoln, NE, USA) with different external light sources.

Light curves using the different external light source (LED lamb and HPS) were produced by using

the Licor 6400 but changing the light intensity manually, from a high intensity to no light.

3.2.2 Whole plants gas exchange measurement

A whole plant gas exchange system can monitor the CO2 exchange and water use of the

whole plant rather than just an individual leaf. The whole plant system used resembles an earlier

design used by Dutton et al. (1988). The system was controlled by LabView 2009 software

(National Instruments Canada, Vaudreuil-Dorion, QC, Canada) running on a Dell, Precision 490

(Dell Computers, Round Rock, TX, USA) computer. This LabView 2009 software allowed for the

CO2 concentration control, relative humidity control, temperature control, and light intensity

control in the chambers. There were six clear polycarbonate plant chambers which measure 0.81m

x 0.46m x 0.46m with a glass top giving a total chamber volume of 200L. During experiments using

smaller plants, boxes of known volume were used to decrease the volumes of chamber, which was

necessary to insure CO2 depletion was within the systems detection limits. Two chambers used

illumination with 390W RW LED fixtures from LSGC, two chambers used illumination with 390W

RB LED fixtures from LSGC, and two chambers used illumination with 1000W HPS lights from

Philips. The light I used were the same to that in the lisianthus paper (Lanoue et al., 2017). The

spectrum of the light was shown in Figure 3.3. At the top of the chambers, which were illuminated

by LED lights, there was a dimmable setting which allowed the light intensity to be variable. For

13

the chambers under HPS, light intensity was set by lifting the lights higher away from the chambers

or by adding shade clothes to the top of the chambers. Also, there was a water bath placed between

the HPS light and the chamber in order to avoid overheating of the chamber. All chambers were

covered with aluminum foil on the outside to prevent light from other lights from entering the

chambers and to prevent light loss lower in the chambers.

Li-COR quantum sensors (LI-190SA, Li-COR Inc. Lincoln, NE, USA) were placed at the

top of the plant canopy to determine the light intensity. The chambers were sealed by a

polycarbonate door with 16 wing nut screws after the light intensity was set. There were 2 modes

of the system: an “open” and “closed” mode. At the beginning, compressed air was passed through

a purge gas generator (CO2 Adsorber, Puregas, Broomfield, CO, USA), which scrubbed part of the

CO2. Then, the desired concentration CO2 was established by adding pure CO2 back into the air

stream in that experiment and the mixed air was directed into the chambers. Every 20 seconds, CO2

and relative humidity levels were checked in the chambers (1 to 6) by an infrared gas analyzer

(IRGA; Li-COR CO2/H2O Gas analyzer 840, Lincoln, NE, USA). Each chamber was then sampled

in sequence every 90 seconds with the first 30 seconds being used to flush the sample lines to

prevent carry over effects from the previous chamber. The next 60 seconds of the sampling period

was used for the net carbon exchange rate calculation (Equation 2.1): where Vol is the chamber

volume (L); Cinitial is the initial CO2 concentration during NCER measurement (μL L-1); Cfinal is

the final CO2 concentration (μL L-1); 0.0821 s the gas constant (L °K-1 mol-1); T is the temperature

of the chamber air (°K); and Δt is the elapse time during sampling (s) (Dutton et al., 1988).

Equation 2.1:

𝑁𝐶𝐸𝑅= (𝐶initial−𝐶final)/0.0821×𝑇×Δ𝑡

In the whole plant gas exchange experiment, the photoperiod was set to 16/8h for LD and

12/12h for SD, with the light level of 500±10 μmol m-2 s-1 PAR. Relative humidity was kept

constantly at 50±5% during the whole experiment. The temperature was set to 22/19°C in day and

night respectively. Plants were placed into the test chambers around 3pm and able to acclimate for

the rest of the day and night period. The next morning, lights would turn on at 6am and shut off at

10pm for LD 16/8h period or turn on at 6am and shut off at 6pm for SD 12/12h period. The next

day, plants were taken out of the test chamber and the leaf area would be measured by the leaf area

meter. The roots were cleaned by washing and then the leaves, stems and roots were dried in the

oven at 70°C for 48h. The dry weight of different parts was measured using a balance.

14

An electronic balance was placed inside the chamber to measure continuously the mass of

the plants and growing media. Changes in mass over time were due to the water losses through

evaporation from the media and plant transpiration. Repeat experiments without plants using the

pots and media alone at the same conditions were conducted to estimate the evaporation loses.

These estimates were subtracted from the total water loses to calculate the transpiration rate and

water use efficiency.

15

Figure 3.3: Light spectrum of HPS, RB and RW LED used in the whole plant gas exchange

system. The data comes from the previous work on tomato and lisianthus (Lanoue et al., 2017).

Wavelength (nm)

400 500 600 700

Sp

ectr

al C

om

po

sitio

n (

%)

0

20

40

60

80

100

HPS

Red-Blue LED

Red-White LED

16

Figure 3.4: Overview of whole plant gas exchange system.

17

3.2.2.1 Research greenhouse chrysanthemums whole plants gas exchange

Research greenhouse chrysanthemums whole plants gas exchange experiments began on

Jan 27th, 2017 and continued every 2 days until Feb 8th, 2017 for LD plants. The SD plants were

tested from Feb 13th to Feb 19th.

Acclimated plants, which were plants grown under 3 types of supplemental light (i.e., HPS,

RB and RW), were randomly selected from research greenhouse and put into whole plant gas

exchange chamber with the same light source. Non-acclimated plants, which were plants grown

under ambient, were tested in the whole plant gas exchange system under all 3 light conditions (i.e.,

HPS, RB and RW).

3.2.2.2 Growth Chamber chrysanthemums whole plants gas exchange

Growth Chamber chrysanthemums whole plants gas exchange experiments were from July

7th to 27th of 2016 and from Jan 5th to Feb 21st. For LD, chrysanthemums were tested in the third

week. For SD, chrysanthemums were tested after the 2 weeks changing into the SD photoperiod.

Plants were randomly selected from growth chamber and put into whole plant gas exchange

chamber under 3 light treatments (i.e., HPS, RB and RW).

18

4. Results

4.1 Research greenhouse chrysanthemums

4.1.1 Chrysanthemums growth and development in research greenhouse

The heights taken every week show that plants under all the light treatments grew similarly

during the first 2 weeks (Fig.4.1). After the 3rd week, plants under the supplemental lights began to

show the enhanced growth in terms of the plant height which continued almost until the end of the

experiment. Among the supplemental light treatments (i.e., HPS, RB and RW), all the light

treatments provided the similar enhanced effect on the plant height throughout the whole

experiment.

Figure 4.2 shows the SPAD readings of every week during the research greenhouse

experiment. Generally, the overall trends of the different supplemental light treatments were similar.

Under HPS, RB and RW, the SPAD reading was slowly increasing in LD, from the start to the third

week. After changing into SD, it stayed stable for one week and increased more quickly from then

on. In contrast, for Amb chrysanthemums, there was a dramatic difference during week 1 to week

3, which was illustrated by a significant decrease in SPAD readings during this period.

Both height and SPAD reading show the greatest effects between second to fifth week, and

that might because during that time, the weather was almost cloudy so that there was low light

period.

At final harvest, destructive measurements were done to get the leaf area, weight of different

parts and the number of flowers (Fig.4.3). Plants under RB had the largest total leaf area, followed

by the leaf area of RW grown plants. In the contrast, the leaf area of plants under HPS was not

significant different to that of ambient grown plants, which showed that HPS did not enhance the

expansion of leaves compared to the ambient plants. When comparing the open flower number, all

3 types of artificial lights dramatically increased the number of open flowers versus that of the

ambient plants. There was no significant difference among flower number under HPS and the 2

LEDs.

Figure 4.4 shows the dry weight (DW) both for total and the different parts of the plants. In

total dry weight (E), plants under RB were the heaviest one, followed by plants under HPS and RW.

Plants that grew under ambient light had the least biomass. The same pattern also appeared for all

the different parts of the plants. RB provided the most enhanced effect in weight of plant stem (B)

and total weight (E). RW and HPS resulted in similar weight in these four parts.

19

Figure 4.1: Height of chrysanthemums grown in the research greenhouse. The height of

chrysanthemums grown under Amb, HPS, RB and RW lighting was measured every week after

transplanting. Every point is the mean of 6 plants ± standard error (SE). The top bars show the

different photoperiods (LD and SD).

Time after Transplant (Weeks)

0 1 2 3 4 5 6 7 8 9 10

He

igh

t (m

)

0.0

0.2

0.4

0.6

0.8

1.0

Amb

HPS

RB

RW

LD SD

LD gas exchange

SD gas exchange

Final harvest

20

Figure 4.2: SPAD reading of chrysanthemums grown in research greenhouse. The SPAD reading

of chrysanthemums grow under Amb, HPS, RB and RW lighting was measured every week after

transplanting. Every point is the mean of 6 plants ± SE. The top bars show the different

photoperiods (LD and SD).

Time after Transplant (weeks)

0 1 2 3 4 5 6 7 8 9 10

SP

AD

readin

g

30

40

50

60

70

80

Amb

HPS

RB

RW

LD SD

LD gas exchange

SD gas exchange

Final harvest

21

Figure 4.3: Leaf area (A) and open flower number (B) of chrysanthemums grown in the research

greenhouse at final harvest. Every bar shows the mean of 10 plants ± SE under different light

treatments. Letters (a, b) represent the statistical difference among light treatments based on a one-

way ANOVA with a Tukey Kramer adjustment at p< 0.05.

Amb HPS RB RW

Leaf A

rea (

m2)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

Amb HPS RB RW

Open flo

wer

num

ber

0

2

4

6

8

10

12

14

16

bb

a

ab

b

a aa

A

B

22

Figure 4.4: Dry weight of different parts of chrysanthemums grown in the research greenhouse at

final harvest. Every bar shows the mean of 10 plants ± SE under different light treatments. Letters

(a, b, c) represent the statistical difference among light treatments based on a one-way ANOVA

with a Tukey Kramer adjustment at p< 0.05.

Total

Amb HPS RB RW

Y D

ata

0

5

10

15

20

25

Flower

Amb HPS RB RW

0

5

10

15

20

25

Leaf

Amb HPS RB RW

0

5

10

15

20

25

Stem

Amb HPS RB RW

0

5

10

15

20

25

Root

Amb HPS RB RW

Weig

ht

(g)

0

5

10

15

20

25

c ab ab

bb

a

b

cab

abc

cab

a

bc

c

b

a

b

A B C D E

23

4.1.2 Chrysanthemum whole plant gas exchange of research greenhouse grown plants

Figure 4.5 illustrates a comparison of long day non-acclimated plants versus acclimated plants

in terms of net carbon exchange rate (NCER), transpiration and WUE. Both non-acclimated and

acclimated plants had similar patterns of NCER under all 3 light treatments during the 24 hours

period: NCER increased a little from the first hour to the second, then remained at similar level

during the rest of the daytime (Fig.4.5 A and B). During daytime, plants under HPS had the highest

NCER in both non-acclimated and acclimated plants, while the 2 LED light treatments had similar

NCERs. After the lights were shut down at the end of the sixteenth hour, the NCER dramatically

dropped from positive to the negative values, and remained steady during the nighttime. During

nighttime, the NCER of all 3 supplemental light treatments were similar and stable. The non-

acclimated plants also had similar transpiration diel pattern with the acclimated plants (Fig.4.5 C

and D). During daytime, transpiration kept increasing from the first hour to the fifth hour, then

stayed at a peak for 4 hours. A decrease in transpiration was followed from the ninth hour to the

end of daytime. During nighttime, transpiration was stable. However, a difference in transpiration

appeared between non-acclimated and acclimated plants. For non-acclimated plants, RW treatment

had the highest transpiration during the daytime, followed with RB and HPS. In the contrast, HPS

treatment had the highest transpiration during the daytime in the acclimated plants, followed by the

RB and RW treatments. WUE showed similar diel patterns in both non-acclimated and acclimated

plants (Fig.4.5 E and F). There was a dramatic decrease in WUE from the first hour to the second

hour, then WUE stayed more less stable with a little decrease until the afternoon and a slight

increase towards the end of light period. The difference between non-acclimated and acclimated

plants was that WUE of non-acclimated plants under HPS had the highest rate, compared to those

under the RW and RB treatments, while the 3 supplemental light treatments resulted in similar

WUE for the acclimated plants.

Figure 4.6 shows NCER of non-acclimated and acclimated plants on 3 different bases: per

plant, per dry weight (g) and per leaf area (m2). The positive bars illustrate the average daytime

NCER values, which are the photosynthetic rates (Pn), while the negative bars represent the average

nighttime NCER values, which are the dark respiration rates (Rd). In general, there were no

significant differences among different light treatments in both non-acclimated and acclimated

plants on a per plant basis (Fig.4.6 A and B). Also, the values were similar under the same light

treatment between non-acclimated and acclimated plants (Fig.4.6 A and B) on a per plant basis. On

a per dry matter basis (Fig.4.6 C and D), NCER still did not show the significant differences among

the three supplemental light treatments within the same growth condition (non-acclimated or

24

acclimated). But there was a significant difference between non-acclimated and acclimated

chrysanthemums under the same light treatment. The acclimated plants had the higher

photosynthesis than those of non-acclimated plants. Furthermore, NCER based on leaf area (Fig.4.6

E and F) showed a different pattern between non-acclimated and acclimated plants: plants grown

under HPS had higher daytime average values than the other 2 LED light treatments grown plants,

although the nighttime average values were similar. Moreover, although acclimated plants had

similar values on a per plant basis NCER with those of the non-acclimated plants (Fig.4.6 A and

B), plants in acclimated condition generated higher values under the 3 light treatments respectively,

on a per dry matter (Fig.4.6 C and D) and a per leaf area bases (Fig.4.6 E and F), than non-

acclimated ones.

Figure 4.7 shows the daily carbon gain on a per plant, dry matter and leaf area bases. For non-

acclimated or acclimated plants only, there were no significant differences in carbon gain among

the three supplemental light treatments on a per plant basis (Fig.4.7 A and B). Also, there were no

significant differences in carbon gain between non-acclimated and acclimated plants under the

same light treatment. Carbon gain on a dry matter basis also showed no significant differences

among the three supplemental light treatments both in either non-acclimated or acclimated plants

(Fig.4.7 C and D). However, there was a significant difference between non-acclimated and

acclimated plants under the same light treatment (Fig.4.7 C and D). Acclimated plants had the

higher carbon gain than that of non-acclimated plants on a dry weight basis. Carbon gain on a per

leaf area basis is illustrated in panel E and F of Figure 4.7. Generally, HPS treatment enhanced

carbon gain on a leaf area basis, followed by the 2 LED light treatments in acclimated plants

(Fig.4.7 F). But there was no significant difference among the three supplemental light treatments

in non-acclimated plants (Fig.4.7 E). When comparing panel E and F in Figure 4.7, non-acclimated

and acclimated plants had similar C gain under the HPS and RW treatments, but acclimated plants

had higher values under the RB light treatment.

Figure 4.8 illustrates the average transpiration and WUE during LD. For both non-acclimated

and acclimated plants there were no significant differences in transpiration among the three

supplemental light treatments (Fig.4.8 A and B). However, acclimated plants under HPS had the

highest transpiration rates (Fig.4.8 B). In contrast, compared to the responses of transpiration above,

WUE showed different patterns between non-acclimated and acclimated plants (Fig.4.8 C and D).

Non-acclimated plants showed the highest WUE under HPS treatment, followed by RB and RW

treatments (Fig.4.8 C). However, acclimated plants had similar WUE values among the three

25

supplemental light treatments (Fig.4.8 D). There were no differences between non-acclimated and

acclimated plants under each light (Fig.4.8 C and D).

26

Figure 4.5: Hourly whole plant NCER, transpiration and WUE of non-acclimated (A, C and E)

and acclimated (B, D and F) plants grown in the research greenhouse during LD. Non-acclimated

plants, chrysanthemums grown under ambient light, were tested in the whole plant system under

the 3 supplemental light treatments. Acclimated plants, chrysanthemums grown under the 3

supplemental light treatments, were tested in the whole plant systems under the same growth lights.

The light intensity was set at 500±10 μmol m-2 s-1 PAR for 16h (top white bar) followed by an 8h

(top black bar) dark period. Every point represents the mean of 6 replicates ± SE for panel A, C

and E and 8 replicates ± SE for panel B, D and F.

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292

NC

ER

(

mol C

O2 m

-2 s

-1)

-5

0

5

10

15

20

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292

NC

ER

(

mol C

O2 m

-2 s

-1)

-5

0

5

10

15

20

TIME

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292N.a.N.

Tra

nspiration (

mm

ol H

20 m

-2 s

-1)

0.0

0.5

1.0

1.5

2.0

2.5

TIME

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292

Tra

nspiration (

mm

ol H

20 m

-2 s

-1)

0.0

0.5

1.0

1.5

2.0

2.5

TIME (hh:mm:ss)

06:00:00 10:00:00 14:00:00 18:00:00 22:00:00 02:00:00 06:00:00

WU

E (

mol C

O2/ m

mol H

2O

)

0

2

4

6

8

10

12

14

16

HPS

RB

RW

TIME (hh:mm:ss)

06:00:00 10:00:00 14:00:00 18:00:00 22:00:00 02:00:00 06:00:00

WU

E (

mol C

O2/ m

mol H

2O

)

0

2

4

6

8

10

12

14

16

HPS

RB

RW

A B

C D

E F

27

Figure 4.6: Daytime and nighttime average whole plant NCER of non-acclimated (A, C and E) and

acclimated (B, D and F) plants grown in the research greenhouse during LD. NCERs are shown on

a per plant (A, B), dry weight (C, D) and leaf area (E, F) basis. Plants were placed in the whole

plant NCER system under either HPS, RB, or RW lights with a light intensity of 500±10 μmol m-2

s-1 for LD (16h light period followed by an 8h dark period). Values represent the daytime or

nighttime means of 6 replicates ± SE for panel A, C and E and 8 replicates ± SE for panel B, D and

F. Upper case letters (A, B, or X, Y) represent statistical significances in daytime or nighttime

NCER among light treatments within each panel. Lower case letters (a, b, or x, y) represent

statistical significances between non-acclimated and acclimated under the same light treatment.

Statistical differences were determined by a one-way ANOVA with a Tukey’s-Kramer adjustment

(p<0.05).

28

HPS RB RW

0.0

0.5

1.0

1.5

HPS RB RW

-0.05

0.00

0.05

0.10

0.15

0.20

HPS RB RW

0

5

10

15

HPS RB RW

NC

ER

(m

ol C

O2 p

lan

t-1s

-1)

0.0

0.5

1.0

1.5

HPS RB RW

NC

ER

(m

ol C

O2 g

-1s

-1)

-0.05

0.00

0.05

0.10

0.15

0.20

HPS RB RW

NC

ER

(m

ol C

O2 m

-2s

-1)

0

5

10

15

A B

C D

E F

AaAa Aa Aa Aa Aa

Xy Xx Xx Xx Xx Xx

Ab Ab Ab

Aa Aa Aa

Xx Xx Xx Xx Xx Xy

Aa

Ab Aa

AaBa

Ba

Xx Xx Xx Xx Xx Xx

29

Figure 4.7: Daily whole plant carbon gain of non-acclimated (A, C and E) and acclimated (B, D

and F) plants grown in the research greenhouse during LD. Carbon gains are shown in plant (A, B),

dry weight (C, D) and leaf area (E, F) basis. Plants were placed in the whole plant NCER system

under either HPS, RB, or RW lights with a light intensity of 500±10 μmol m-2 s-1 for LD (16h

followed by an 8h dark period). Values represent the means of 6 replicates ± SE for panel A, C and

E and 8 replicates ± SE for panel B, D and F. Upper case letters (A, B) represent statistical

significances among light treatments within each panel. Lower case letters (a, b) represent statistical

significances between non-acclimated and acclimated plants under the same light treatment.

Statistic differences were determined by a one-way ANOVA with a Tukey’s-Kramer adjustment

(p<0.05).

30

HPS RB RW

0

100

200

300

400

500

600

HPS RB RW

0

20

40

60

80

100

120

HPS RB RW

0

2000

4000

6000

8000

HPS RB RW

C g

ain

(m

g C

pla

nt-1

d-1

)

0

100

200

300

400

500

600

HPS RB RW

C g

ain

(m

g C

g-1

d-1

)

0

20

40

60

80

100

120

HPS RB RW

C g

ain

(m

g C

m-2

d-1

)

0

2000

4000

6000

8000

AaAa Aa

AaAa

Aa

AbAb Ab

Aa Aa Aa

Aa

AbAa

Aa

BaBa

A B

C D

E F

31

Figure 4.8: Average whole plant transpiration and WUE of non-acclimated (A, C) and acclimated

(B, D) plants grown in the research greenhouse during LD. Plants were placed in the whole plant

NCER system under either HPS, RB, or RW lights with a light intensity of 500±10 μmol m-2 s-1 for

LD (16h followed by an 8h dark period). Values represent the means of 6 replicates ± SE for panel

A and C and 8 replicates ± SE for panel B and D. Upper case letter (A, B) represent statistical

significances within non-acclimated or acclimated plants in each panel. Lower case letter (a, b)

represent statistical significances between non-acclimated and acclimated plants under the same

light treatment. Statistic differences were determined by a one-way ANOVA with a Tukey’s-

Kramer adjustment (p<0.05).

HPS RB RW

E (

mm

ol H

2O

m-2

s-1

)

0.0

0.5

1.0

1.5

2.0

HPS RB RW

WU

E (

mol C

mm

ol-1

H20

)

0

2

4

6

8

HPS RB RW

Tra

nspiration (

mm

ol H

2O

m-2

s-1

)

0.0

0.5

1.0

1.5

2.0

HPS RB RW

WU

E (

mol C

mm

ol-1

H20

)

0

2

4

6

8

A B

C D

Ab AaAa

Aa

Aa Aa

Aa

Ba BaAa Aa Aa

32

Figure 4.9 shows the acclimated plant hourly NCER (A and B), transpiration (C and D) and

WUE (E and F) during LD (A, C and E) and SD (B, D and F). NCER of plants under the three

supplemental light treatments had similar patterns during both LD and SD: an increase from the 1st

hour to the 2nd hour, then stayed stable until the end of daytime (Fig.4.9 A and B). At nighttime,

plant NCER dropped dramatically into negative values and remained relative steady (slightly

higher values at the start of the dark period) under all supplemental light treatments (Fig.4.9 A and

B). All plants under HPS had higher hourly NCER values than those of RB and RW during both

LD and SD (Fig.4.9 A and B). Transpiration increased slowly from the 1st to 7th hour and then

decreased from the 7th hour to the end of daytime under all the supplemental light treatments during

both LD and SD (Fig.4.9 C and D). During nighttime, transpiration under the three supplemental

light treatments were similarly stable with a slightly increase towards the end of the dark period

(Fig.4.9 C and D). The interesting point here was that during the daytime, plants under HPS showed

an obviously higher transpiration rates than under two LED light treatments during LD (Fig.4.9 C),

but during SD, transpiration rates were similar to those under RW and plants under RB had the

highest rates (Fig.4.9 D). WUE illustrated similar patterns during both LD and SD, which was

decreasing from the 1st hour to the 7th hour and then increasing slightly towards the end of daytime

(Fig.4.9 E and F). The dramatic difference here was that during LD, the plants had similar WUE

values among light treatments over the daytime (Fig.4.9 E), however, during SD, WUE was

different among the three supplemental light treatments, with HPS having higher rates followed by

RB and RW (Fig.4.9 F).

Figure 4.10 shows the daytime and nighttime average NCER during LD and SD of research

greenhouse chrysanthemums grown under HPS, RB and RW light treatments. During LD, plants

had similar Rd (negative values) based on a per plant, dry matter and leaf area basis among the

three supplemental light treatments (Fig.4.10 A, C and E). Pn (positive values) of plants grown

under HPS, RB and RW were similar based on per plant and dry matter basis (Fig.4.10 A and C).

But on a leaf area basis, HPS enhanced Pn much more than RB and RW did (Fig.4.10 E). During

SD, Rd were similar on a dry matter and leaf area basis among the three supplemental light

treatments (Fig.4.10 D and F). However, there were significant differences on a per plant basis;

plants under RB and RW had higher Rd, followed by HPS (Fig.4.10 B). Pn values were similar on

a per plant and dry matter basis among the three supplemental light treatments (Fig.4.10 B and D),

but HPS helped chrysanthemums achieve a higher Pn than RB and RW did on a leaf area basis

(Fig.4.10 F).

33

Most notable while comparing LD to SD, Rd were significantly lower during SD than during

LD among all three supplemental light treatments on a dry matter (Fig.4.10 C and D) and leaf area

(Fig.4.10 E and F) basis. But plants had higher Rd during SD than during LD on a per plant basis

(Fig.4.10 A and B) under each of the three supplemental light treatments. Pn of plants was higher

during LD than during SD on a dry matter (Fig.4.10 C and D) and leaf area (Fig.4.10 E and F) basis.

However, every plant had a higher Pn during SD than LD under all lights (Fig.4.10 A and B).

Figure 4.11 illustrates a comparison of whole plant carbon gains of acclimated plants grown

under the three supplemental light treatments during LD and SD. During both LD and SD, plants

grown under the three supplemental light treatments had similar carbon gain on a per plant (Fig.4.11

A and B) or dry matter basis (Fig.4.11 C and D). But on a leaf area basis, HPS increased carbon

gain the most, followed by RB and RW (Fig.4.11 E and F). Comparing between LD and SD, plants

had higher carbon gains during LD than during SD on a dry matter (Fig.4.11 C and D) and leaf area

(Fig.4.11 E and F) basis under each light treatment respectively. However, every plant had higher

carbon gain during SD than LD under each light treatment (Fig.4.11 A and B).

Figure 4.12 illustrates transpiration and WUE comparisons of research acclimated

chrysanthemums between LD (A and C) and SD (B and D). During LD, acclimated plants had

similar transpiration and WUE among the three supplemental light treatments (Fig.4.12 A and C).

During SD, plants also showed similar transpiration (Fig.4.12 B), however, WUE was higher under

the HPS than under two LED light treatments (Fig.4.12 D). When comparing LD and SD,

acclimated plants had a higher transpiration during LD than during SD under each supplemental

light treatment (Fig.4.12 A and B). For WUE, there was no significant difference under HPS

between LD and SD (Fig.4.12 C and D). But, WUE was lower under the RB and RW light treatment

during LD than during SD (Fig.4.12 C and D).

34

Figure 4.9: Hourly whole plant NCER (A, B), transpiration (C, D) and WUE (E, F) of acclimated

plants grown in the research greenhouse during LD (A, C and E) and SD (B, D and F). Plants were

placed in the whole plant system under HPS, RB, or RW lights with a light intensity of 500±10

μmol m-2 s-1 for LD (16h followed by an 8h dark period) or SD (12h followed by a 12h dark period).

Every point represents the mean of 8 replicates ± SE. The top bars show different time of day, the

white bar is daytime, and the black bar is nighttime.

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292N.a.N.

-5

0

5

10

15

20

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292

NC

ER

(

mol C

O2 m

-2 s

-1)

-5

0

5

10

15

20

TIME

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292N.a.N.

Tra

nspiration (

mm

ol H

20 m

-2 s

-1)

0.0

0.5

1.0

1.5

2.0

2.5

TIME

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292N.a.N.

Tra

nspiration (

mm

ol H

20 m

-2 s

-1)

0.0

0.5

1.0

1.5

2.0

2.5

TIME (hh:mm:ss)

06:00:00 10:00:00 14:00:00 18:00:00 22:00:00 02:00:00 06:00:00

WU

E (

mol C

O2/

mm

ol H

2O

)

0

2

4

6

8

10

12

14

16

HPS

RB

RW

A B

TIME (hh:mm:ss)

06:00:00 10:00:00 14:00:00 18:00:00 22:00:00 02:00:00 06:00:00

WU

E (

mol C

O2/

mm

ol H

2O

)

0

2

4

6

8

10

12

14

16

HPS

RB

RW

C D

E F

35

Figure 4.10: Daytime and nighttime average whole plant NCER of acclimated plants grown in the

research greenhouse during LD (A, C and E) and SD (B, D and F). NCERs are shown in plant (A,

B), dry weight (C, D) and leaf area (E, F) basis. Plants were placed in the whole plant system under

either HPS, RB, or RW lights with a light intensity of 500±10 μmol m-2 s-1 for LD (16h followed

by an 8h dark period) or SD (12h followed by a 12h dark period). Values represent the daytime or

nighttime means of 8 replicates ± SE. Upper case letters (A, B, or X, Y) represent statistical

significances in daytime or nighttime NCER among light treatments within each photoperiod (LD

or SD). Lower case letters (a, b, or x, y) represent statistical significances between LD and SD

under the same light treatment. Statistical differences were determined by a one-way ANOVA with

a Tukey’s-Kramer adjustment (p<0.05).

36

HPS RB RW

NC

ER

(m

ol C

O2 p

lan

t-1s

-1)

0.0

0.5

1.0

1.5

HPS RB RW

NC

ER

(m

ol C

O2 g

-1s

-1)

-0.05

0.00

0.05

0.10

0.15

0.20

HPS RB RW

NC

ER

(m

ol C

O2 m

-2s

-1)

0

5

10

15

HPS RB RW

NC

ER

(m

ol C

O2 p

lan

t-1s

-1)

0.0

0.5

1.0

1.5

HPS RB RW

NC

ER

(m

ol C

O2 g

-1s

-1)

-0.05

0.00

0.05

0.10

0.15

0.20

HPS RB RW

NC

ER

(m

ol C

O2 m

-2s

-1)

0

5

10

15

Ab Ab Ab

Aa Aa Aa

Xx Xx Xx Xy Yy XYy

Aa Aa Aa

AbAb Ab

Xy Xy XyXx Xx Xx

AaBa

BaAb

Bb Bb

Xy Xy XyXx Xx Xx

A B

C D

E F

37

Figure 4.11: Daily whole plant carbon gain of acclimated plants grown in the research greenhouse

during LD (A, C and E) and SD (B, D and F). Plants were placed in the whole plant system under

HPS, RB, or RW lights with a light intensity of 500±10 μmol m-2 s-1 for LD (16h followed by an

8h dark period) or SD (12h followed by a 12h dark period). Values represent the means of 8

replicates ± SE. Upper case letters (A, B) represent statistical significances among light treatments

within photoperiod (LD or SD). Lower case letters (a, b) represent statistical significances between

LD and SD under the same light treatment. Statistical differences were determined by a one-way

ANOVA with a Tukey’s-Kramer adjustment (p<0.05).

38

HPS RB RW

C g

ain

(m

g C

pla

nt-1

d-1

)

0

100

200

300

400

500

600

HPS RB RW

C g

ain

(m

g C

g-1

d-1

)

0

20

40

60

80

100

120

HPS RB RW

C g

ain

(m

g C

m-2

d-1

)

0

2000

4000

6000

8000

HPS RB RW

C g

ain

(m

g C

pla

nt-1

d-1

)

0

100

200

300

400

500

600

HPS RB RW

C g

ain

(m

g C

g-1

d-1

)

0

20

40

60

80

100

120

HPS RB RW

C g

ain

(m

g C

m-2

d-1

)

0

2000

4000

6000

8000

Ab Ab Ab

AaAa Aa

Aa Aa Aa

AbAb Ab

Aa

BaBa

Ab

Bb Bb

A B

C D

E F

39

Figure 4.12: Average whole plant transpiration and WUE of acclimated plants grown in the

research greenhouse during LD (A, C) and SD (B, D). Plants were placed in the whole plant system

under either HPS, RB, or RW lights with a light intensity of 500±10 μmol m-2 s-1 for LD (16h

followed by an 8h dark period) or SD (12h followed by a 12h dark period). Values represent the

daytime means of 8 replicates ± SE. Upper case letters (A, B) represent statistical significances

among light treatments within photoperiod (LD or SD). Lower case letters (a, b) represent statistical

significances between LD and SD under the same light treatment. Statistical differences were

determined by a one-way ANOVA with a Tukey’s-Kramer adjustment (p<0.05).

HPS RB RW

E (

mm

ol H

2O

m-2

s-1

)

0.0

0.5

1.0

1.5

2.0

HPS RB RW

WU

E (

mol C

mm

ol-1

H20

)

0

2

4

6

8

HPS RB RW

Tra

nspiration (

mm

ol H

2O

m-2

s-1

)

0.0

0.5

1.0

1.5

2.0

HPS RB RW

WU

E (

mol C

mm

ol-1

H20

)

0

2

4

6

8

A B

C D

Aa

Aa Aa

Ab

AbAb

Aa Aa Aa

Aa

Bb

Bb

40

Table 4.1 shows data of research greenhouse plants used to obtain the whole plant

measurements during LD and SD. During LD, there was no significant difference in leaf area (LA)

and DW among the three supplemental light treatments. However, plants grown under RW had

lower specific leaf weight (SLW) than those of HPS and RB. During SD, similar to LD results,

there was no significant difference in LA and DW among the three supplemental light treatments.

But plants grown under HPS had higher SLW than those grown under RB or RW.

Comparing LD and SD, plants had a higher LA and DW during SD than those of LD. Plants

under HPS and RW had the similar SLW during both LD and SD, but growth under RB resulted in

higher SLW during LD than SD.

41

Table 4.1: Whole plant leaf area (LA), dry weight (DW) and specific leaf weight (SLW) of research

greenhouse plants used for whole plant gas exchange measurements during LD and SD. All values

represent the mean with the standard error (±), shown in parentheses. Upper case letters (A, B)

represent statistical significances among the light treatments in the same photoperiod (LD or SD).

Lower case letters (a, b) represent statistical significances between LD and SD under the same light.

Statistical differences were determined by a one-way ANOVA with a Tukey’s-Kramer adjustment

(p<0.05).

light LA(m2) DW(g) SLW(g m-2)

LD

HPS 0.0223(0.0010)Ab 1.77(0.11)Ab 46.78(2.19)Aa

RB 0.0266(0.0019)Ab 1.96(0.15)Ab 42.01(0.92)ABa

RW 0.0260(0.0012)Ab 1.87(0.11)Ab 41.37(0.94)Ba

SD

HPS 0.0675(0.0048)Aa 5.28(0.36)Aa 44.26(0.71)Aa

RB 0.0785(0.0024)Aa 5.59(0.24)Aa 38.52(0.89)Bb

RW 0.0758(0.0029)Aa 5.25(0.17)Aa 38.88(0.80)Ba

42

4.1.3 Chrysanthemum leaf gas exchange of research greenhouse grown plants

Figure 4.13 shows the research greenhouse grown chrysanthemums light curves under

different supplementary light treatments during LD. The photosynthetic rate of leaves under the

three light treatments responded in a similar pattern: kept increasing with the light intensity

increasing from 0 to 800 μmol m−2 s−1, then got to a plateau (Fig.4.13A). Based on regression

analyses shown in Figure 4.14, there were no significant differences in Pnmax among three light

treatments (Table 4.2). Transpiration rates (Fig. 4.13 B) of leaves under the three light treatments

illustrated different trends: HPS caused E to continuously increase, while the RW increased E from

0 to 400 μmol m−2 s−1of PAR and then decrease a little, but leaf E under RB revealed a larger

increase from 0 to 200 μmol m−2 s−1, kept steady until 400 μmol m−2 s−1 and increased gradually

after that. Leaf WUE (Fig. 4.13 C) under the three supplemental lights had a similar pattern, which

was increasing from 0 to 400 μmol m−2 s−1 and then remain stable at the higher light levels. There

were no significant differences in any leaf parameter among the three supplemental lights (Table

4.2).

43

Figure 4.13: Light curves for leaf NCER (A), transpiration (B) and WUE (C) of research

greenhouse grown chrysanthemums during LD under the different supplemental lights.

Chrysanthemums grown under different light treatment (HPS, RB, RW) were tested under their

own grown light. Every point represents the mean of 5 replicates ± SE.

44

X Data

0 200 400 600 800 1000 1200 1400

Lea

f N

CE

R (

mo

l C

O2 m

-2 s

-1)

-5

0

5

10

15

20

25

30

X Data

0 200 400 600 800 1000 1200 1400

Tra

nsp

ira

tio

n (

mm

ol H

2O

m-2

s-1

)

0

1

2

3

4

5

Light intensity (mol m-2

s-1

)

0 200 400 600 800 1000 1200 1400 1600

WU

E (

mo

l C

O2 m

mo

l-1 H

20)

0

5

10

15

HPS

RB

RW

A

B

C

45

Figure 4.14: Leaf NCER light response curves of research greenhouse grown chrysanthemums

during LD under different supplemental light sources. Chrysanthemums grown under different light

treatment (HPS, RB, RW) were tested under their own grown light. The regression lines are

calculated using the equation f = yo + a (1−e(−b*x)) and 5 replications for each light treatment.

light intensity (mol m-2

s-1

)

0 200 400 600 800 1000 1200 1400 1600

Leaf

NC

ER

(

mol C

O2 m

-2 s

-1)

0

5

10

15

20

25

30

HPS

RB

RW

46

Table 4.2: A summary of the major physiological traits determined by analysis of leaf gas exchanges of research greenhouse chrysanthemums

during LD. Chrysanthemums grown under different light treatment (HPS, RB, RW) were tested under their own grown light. Respiration rate (Rd),

the light compensation point (LCP), maximum quantum yield (YQ), and Pnmax were calculated using the equation f = yo + a (1−e(−b*x)), while Pn500,

Transpiration500, and WUE500 are values at 500 μmol m−2 s−1 PAR for each light treatment tested. All values represent the mean of 5 leaf replicates

with the standard error (±), shown in parentheses. Lower case letters (a) represent statistical significances among light treatment. Statistical

differences were determined by a one-way ANOVA with a Tukey’s-Kramer adjustment (p<0.05).

light treatment Rd

(µmol m-2 s-1) LCP

(µmol m-2 s-1) YQ

Pnmax

(µmol m-2 s-1) Pn500

(µmol m-2 s-1)

Transpiration500

(mmol H2O m-2 s-1) WUE500

(µmolCO2/mmolH2O)

Amb . . . . . . .

HPS -1.19(0.06)a 16.64(0.81)a 0.074(0.001)a 22.52(0.60)a 18.06(0.32)a 2.50(0.18)a 7.36(0.46)a

RB -1.44(0.08)a 22.64(1.32)a 0.066(0.001)a 21.49(0.85)a 17.55(0.45)a 3.20(0.35)a 5.78(0.65)a

RW -1.46(0.23)a 20.53(2.44)a 0.073(0.004)a 20.52(0.54)a 16.06(0.94)a 2.76(0.34)a 6.12(0.55)a

47

Figure 4.15 shows leaf data for greenhouse plants grown under different supplemental light

treatments but tested under the Licor 6400 RB light during LD and SD. The data illustrated that

the trend was similar among HPS, RB, RW and the Amb in terms of leaf Pn (Fig.4.15 A and B).

Leaf Pn kept climbing from 0 to 800 PAR and then stayed stable. Leaf transpiration (Fig.4.15 C

and D) revealed a slow increasing trend for plants grown under all the light treatments. Leaf WUE

(Fig. 4.15 E and F) continually increased from 0 to 300 PAR and then stayed stable for all light

treatments.

Based on Figure 4.16 and Table 4.3 plants grown under RB had higher leaf Pn500 than the non-

supplemental treatment (Amb) during LD, but there were no significant differences in Pn500 among

light treatments during SD. In contrast, Pnmax showed no significant difference among HPS, RB,

RW and Amb during both LD and SD.

Based on Table 4.3, most physiological parameters under each light treatment were the same

during LD and SD (Table 4.3; comparison between LD and SD). However, under each of the

supplemental light treatments, leaves showed lower values of LCP and Rd during SD than those

during LD.

48

Figure 4.15: Light curves for leaf NCER (A and B), transpiration (C and D) and WUE (E and F)

of research greenhouse grown chrysanthemums during LD (A, C and E) and SD (B, D and F).

Plants were grown under different light treatments (Amb, HPS, RB, and RW) but tested using the

Licor-6400 RB LED light source. Every point represents the mean of at least 5 replicates ± SE.

X Data

0 200 400 600 800 1000 1200 1400 1600

Leaf

NC

ER

(

mo

l C

O2 m

-2 s

-1)

0

10

20

30

light intensity (mol m-2 s-1)

0 200 400 600 800 1000 1200 1400 1600

E (

mm

ol H

2O

m-2

s-1

)

0

1

2

3

4

5

light intensity (mol m-2 s-1)

0 200 400 600 800 1000 1200 1400 1600

WU

E (

mo

l C

O2 m

mo

l-1 H

20)

0

5

10

15

X Data

0 200 400 600 800 1000 1200 1400

Leaf

NE

CR

(

mo

l C

O2 m

-2 s

-1)

-5

0

5

10

15

20

25

30

light intensity (mol m-2 s-1)

0 200 400 600 800 1000 1200 1400

Tra

nsp

ira

tio

n (

mm

ol H

2O

m-2

s-1

)

0

1

2

3

4

5

light intensity (mol m-2 s-1)

0 200 400 600 800 1000 1200 1400 1600

WU

E (

mo

l C

O2 m

mo

l-1 H

20)

0

5

10

15

Amb

HPS

RB

RW

B

C

A

D

E F

Amb

HPS

RB

RW

49

Figure 4.16: Leaf NCER light response curves of research greenhouse grown chrysanthemums during LD (A) and SD (B). The plants were grown

under different supplemental light treatments (Amb, HPS, RB, and RW) but tested using the Licor-6400 RB LED light source. The regression lines

were calculated using the equation f = yo + a (1−e(−b*x)) and at least 5 replications for each light treatment.

light intensity (mol m-2

s-1

)

0 200 400 600 800 1000 1200 1400 1600

Leaf N

CE

R (

mol C

O2 m

-2 s

-1)

0

5

10

15

20

25

30

B

light intensity (mol m-2

s-1

)

0 200 400 600 800 1000 1200 1400

Leaf N

CE

R (

mol C

O2 m

-2 s

-1)

0

5

10

15

20

25

30

Amb

HPS

RB

RW

Amb

HPS

RB

RW

A

50

Table 4.3: A summary of the major physiological traits determined by analysis of leaf gas exchanges of research greenhouse grown chrysanthemums

during LD and SD. Plants were grown under different light treatments (Amb, HPS, RB, and RW) but tested using the Licor-6400 RB LED light

source. The Rd, LCP, YQ, and Pnmax were calculated using equation f = yo + a (1−e(−b*x)), while Pn500, Transpiration500, and WUE500 are values at 500

μmol m−2 s−1 PAR for each light treatment tested. All values represent the mean of at least 5 leaf replicates with the standard error (±), shown in

parentheses. Upper case letters (A, B) represents statistical significances among the light treatments in the same photoperiod (LD or SD). Lower

case letters (a,b) represent statistical significances under the same light, between LD and SD. Statistical differences were determined by a one-way

ANOVA with a Tukey’s-Kramer adjustment (p<0.05).

light treatment

Rd (µmol m-2 s-1)

LCP

(µmol m-2 s-1) YQ

Pnmax

(µmol m-2 s-1) Pn500

(µmol m-2 s-1) Transpiration500

(mmol H2O m-2 s-1) WUE500

(µmolCO2/mmolH2O)

LD

Amb -1.11(0.23)Aa 12.41(2.68)Aa 0.093(0.002)Aa 17.70(0.71)Aa 14.84(0.46)Ba 1.54(0.68)Aa 9.74(1.77)Aa

HPS -1.40(0.19)Ab 14.89(1.71)Aa 0.097(0.005)Aa 19.85(0.77)Aa 16.36(0.40)ABa 2.28(0.24)Aa 7.63(0.81)Aa

RB -1.30(0.10)Ab 14.68(0.94)Aa 0.092(0.002)Aa 20.58(0.66)Aa 16.82(0.46)Aa 2.48(0.55)Aa 8.17(1.64)Aa

RW -1.19(0.05)Ab 12.84(0.62)Aa 0.096(0.003)Aa 19.76(0.63)Aa 16.54(0.49)ABa 2.55(0.44)Aa 7.40(1.42)Aa

SD

Amb -0.89(0.09)Aa 9.84(0.91)Aa 0.083(0.010)Aa 20.15(1.57)Aa 15.44(1.60)Aa 1.88(0.32)Aa 8.95(1.32)Aa

HPS -0.76(0.07)Aa 8.91(0.75)Ab 0.087(0.005)Aa 19.69(1.07)Aa 16.05(0.88)Aa 2.40(0.34)Aa 7.24(1.00)Aa

RB -0.75(0.20)Aa 8.04(1.78)Ab 0.089(0.007)Aa 18.90(1.60)Aa 15.72(1.37)Aa 1.98(0.27)Aa 8.35(0.62)Aa

RW -0.52(0.05)Aa 6.34(0.77)Ab 0.084(0.003)Ab 17.53(0.83)Aa 14.75(0.36)Aa 1.95(0.26)Aa 8.31(1.32)Aa

51

4.2 Growth chamber chrysanthemums

4.2.1 Chrysanthemums whole plant gas exchange in growth chamber

Figure 4.17 shows the hourly NCER (A, B), transpiration (C, D) and WUE (E, F) of growth

chamber chrysanthemums during LD (A, C, E) and SD (B, D, F). Generally, chamber

chrysanthemums presented similar trend under the three supplemental light treatments during both

LD and SD in hourly NCER, transpiration and WUE. Whole plant NCER increased slowly in the

first hour of the daytime and stayed stable for the rest of daytime (Fig.4.17 A and B). After changing

into nighttime, NCER dropped to negative values and kept same during the night time. Plant

transpiration kept increasing from 6am to 12pm and then it decreased for the rest of the daytime

during both LD and SD (Fig.4.17 C and D). In the nighttime, transpiration decreased firstly and

then increased slowly towards the end of the dark period during both LD and SD. Plant WUE,

during both LD and SD, decreased firstly and increased later in the daytime (Fig.4.17 E and F).

NCER on a per plant, dry matter and leaf area bases are shown in the Figure 4.18. During LD

(A, C and E), there were no statistical differences in the terms of Rd (negative values) among the

three supplemental light treatments (Fig.4.18 A, C and E). NCER during the day, Pn (positive

values) illustrated the similar value on the plant basis (Fig.4.18 A), but plants tested under RW had

the lower Pn compared to plants tested under HPS both on a dry matter and on a leaf area basis

(Fig.4.18 C and E). During SD, all plants had similar Pn during the daytime and Rd during the

nighttime under the three supplemental light treatments, on a per plant, dry matter and leaf area

basis (Fig.4.18 B, D and F). On a per plant basis, every plant under each supplemental light

treatment had a higher Pn and Rd during SD than that during LD (Fig.4.18 A and B). However, on

a dry matter basis (Fig.4.18 C and D), plants showed similar Pn but less Rd during SD than that

during LD under each of the three supplemental light treatments. On leaf area basis (Fig.4.18 E and

F), plants showed a higher Pn and Rd during LD than that during SD.

Figure 4.19 shows the daily carbon gain on per plant (A and B), dry matter (C and D) and leaf

area (E and F) basis during LD (A, C and E) and SD (B, D and F). During LD, every plant (Fig.

4.19 A) had the similar daily carbon gain under HPS, RB and RW. But on dry matter (Fig.4.19 C)

and leaf area (Fig.4.19 E) basis, plants under HPS light showed the highest carbon gain than that

under RW. During SD, plants had similar daily carbon gain value under the three supplemental

light treatments on all bases (Fig.4.19 B, D and F). When comparing LD to SD, every plant had

higher carbon gain on a per plant basis during SD under all lights (Fig.4.19 A and B). However, on

52

a dry matter (Fig.4.19 C and D) and leaf area (Fig.4.19 E and F) basis, plants showed lower carbon

gain during SD than that during LD.

Figure 4.20 shows the average daily transpiration and WUE of growth chamber

chrysanthemums tested under the three supplemental light treatments during LD (A and C) and SD

(B and D). During LD, plants tested under RB light had higher transpiration than HPS and RW

(Fig.4.20 A). In contrast, during SD plants had similar transpiration values among the three tested

light treatments (Fig.4.20 B). Both during LD and SD, plants tested under HPS had the higher WUE

than under RB and RW (Fig.4.20 C and D). Comparing LD with SD, plants showed lower

transpiration during SD under each tested light treatment than that of LD (Fig.4.20 A and B).

However, plants under each tested light treatment had higher WUE during SD than during LD

(Fig.4.20 C and D).

53

Figure 4.17: Hourly whole plant NCER (A, B), transpiration (C, D), and WUE (E, F) of plants

grown in the growth chamber during LD (A, C, E) and SD (B, D, F). Plants were placed in the

whole plant system under HPS, RB, or RW lights with a light intensity of 500 ±10 μmol m-2 s-1 for

LD (16h followed by an 8h dark period) or SD (12h followed by a 12h dark period). Every point

represents the hourly mean value of 16 replicates ± SE for LD and 12 replicates for SD. The top

bars show different time of day, the white bar is daytime, and the black bar is nighttime.

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292N.a.N.

NC

ER

(

mol C

O2 m

-2 s

-1)

-5

0

5

10

15

20

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292N.a.N.

NC

ER

(

mol C

O2 m

-2 s

-1)

-5

0

5

10

15

20

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292

0.0

0.5

1.0

1.5

2.0

2.5

TIME

2415019.27082415019.31252415019.35422415019.39582415019.43752415019.47922415019.52082415019.56252415019.60422415019.64582415019.68752415019.72922415019.77082415019.81252415019.85422415019.89582415019.93752415019.97922415020.02082415020.06252415020.10422415020.14582415020.18752415020.2292

Tra

nspiration (

mm

ol H

20 m

-2 s

-1)

0.0

0.5

1.0

1.5

2.0

2.5

TIME (hh:mm:ss)

06:00:00 10:00:00 14:00:00 18:00:00 22:00:00 02:00:00 06:00:00

WU

E (

mol C

O2/ m

mol H

2O

)

HPS

RB

RW

A B

C D

F

TIME (hh:mm:ss)

06:00:00 10:00:00 14:00:00 18:00:00 22:00:00 02:00:00 06:00:00

WU

E (

mol C

O2/ m

mol H

2O

)

0

2

4

6

8

10

12

14

16

HPS

RB

RW

E

54

Figure 4.18: Daytime and nighttime average NCER of plants grown in the growth chamber during

LD (A, C and E) and SD (B, D and F). NCERs are shown in plant (A, B), dry weight (C, D) and

leaf area (E, F) basis. Plants were placed in the whole plant NCER system under either HPS, RB,

or RW lights with a light intensity of 500±10 μmol m-2 s-1 for LD (16h followed by an 8h dark

period) or SD (12h followed by a 12h dark period). Values represent the daytime or nighttime

means of 16 replicates ± SE for LD and 12 replicates for SD. Upper case letters (A, B, or X, Y)

represent statistical significances in daytime or nighttime NCER among light treatments within

each photoperiod. Lower case letters (a, b, or x, y) represent statistical significances between LD

and SD under the same light treatment. Statistical differences were determined by a one-way

ANOVA with a Tukey’s-Kramer adjustment (p<0.05).

55

HPS RB RW

0.0

0.5

1.0

1.5

X Data

HPS RB RW

-0.05

0.00

0.05

0.10

0.15

0.20

HPS RB RW

0

5

10

15

HPS RB RW

NC

ER

(m

ol C

O2 p

lan

t-1s

-1)

0.0

0.5

1.0

1.5

HPS RB RW

NC

ER

(m

ol C

O2 g

-1s

-1)

-0.05

0.00

0.05

0.10

0.15

0.20

HPS RB RW

NC

ER

(m

ol C

O2 m

-2s

-1)

0

5

10

15

A B

C D

E F

AbAb Ab

Aa

AaAa

Aa ABa BaAa Aa Aa

Aa AaBa Ab Ab Ab

Xx Xx Xx Xy Xy Xy

Xy Xy XyXx Xx Xx

Xy Xy XyXx Xx Xx

56

Figure 4.19: Carbon gain of plants grown in the growth chamber during LD (A, C and E) and SD

(B, D and F). Carbon gains are shown on per plant (A, B), dry weight (C, D) and leaf area (E, F)

basis. Plants were placed in the whole plant NCER system under either HPS, RB, or RW lights

with a light intensity of 500±10 μmol m-2 s-1 for LD (16h followed by an 8h dark period) or SD

(12h followed by a 12h dark period). Values represent the means of 16 replicates ± SE for LD and

12 replicates for SD. Upper case letters (A, B) represent statistical significances among light

treatments within each photoperiod. Lower case letters (a, b) represent statistical significances

between LD and SD under the same light treatment. Statistical differences were determined by a

one-way ANOVA with a Tukey’s-Kramer adjustment (p<0.05).

57

X Data

HPS RB RW

0

200

400

600

HPS RB RW

0

20

40

60

80

100

120

HPS RB RW

0

2000

4000

6000

8000

HPS RB RW

C g

ain

(m

g C

pla

nt-1

d-1

)

0

200

400

600

HPS RB RW

C g

ain

(m

g C

g-1

d-1

)

0

20

40

60

80

100

120

HPS RB RW

C g

ain

(m

g C

m-2

d-1

)

0

2000

4000

6000

8000

A B

C D

E F

Ab

Ab Ab

Aa

AaAa

AaABa Ba

AbAb Ab

AaABa

Ba

AbAb Ab

58

Figure 4.20: Average transpiration and WUE of plants grown in the growth chamber during LD

(A, C) and SD (B, D). Plants were placed in the whole plant NCER system under either HPS, RB,

or RW lights with a light intensity of 500±10 μmol m-2 s-1 for LD (16h followed by an 8h dark

period) or SD (12h followed by a 12h dark period). Values represent the means of 16 replicates ±

SE for LD and 12 replicates for SD. Upper case letters (A, B) represent statistical significances

among light treatments within each photoperiod. Lower case letters (a, b) represent statistical

significances between LD and SD under the same light treatment. Statistical differences were

determined by a one-way ANOVA with a Tukey’s-Kramer adjustment (p<0.05).

HPS RB RW

0.0

0.5

1.0

1.5

2.0

HPS RB RW

0

2

4

6

8

HPS RB RW

Tra

nspiration (

mm

ol H

2O

m-2

s-1

)

0.0

0.5

1.0

1.5

2.0

HPS RB RW

WU

E (

mol C

mm

ol-1

H20

)

0

2

4

6

8

A B

C D

Ba

Aa

Ba

Ab

Ab

Ab

Ab

Bb Bb

Aa

BaBa

59

Table 4.4 shows data of growth chamber plants used for the whole plant measurements

during LD and SD. As expected because all plants were grown in growth chambers under the same

conditions, there was no significant difference in LA, DW and SLW among the three supplemental

light treatments during LD or during SD.

Also, because plants used for the whole plant gas exchange measurements during SD were

at least 2 to 3 weeks older than plants during LD, SD plants had a higher LA and DW than those

of LD. However, SLW was higher during LD than during SD.

60

Table 4.4: LA, DW and SLW of growth chamber plants used for whole plant gas exchange

measurements during LD and SD. All values represent the mean with the standard error (±), shown

in parentheses. Upper case letters (A) represent statistical significances among the light treatments

in the same light period (LD or SD). Lower case letters (a, b) represent statistical significances

under the same light, between LD and SD. Statistical differences were determined by a one-way

ANOVA with a Tukey’s-Kramer adjustment (p<0.05).

light LA(m2) DW(g) SLW(g m-2)

LD

HPS 0.0671(0.0047)Ab 6.35(0.44)Ab 49.54(0.86)Aa

RB 0.0636(0.0045)Ab 6.03(0.43)Ab 49.30(1.37)Aa

RW 0.0697(0.0051)Ab 6.38(0.52)Ab 47.17(0.57)Aa

SD

HPS 0.1694(0.0096)Aa 13.98(1.12)Aa 39.26(0.89)Ab

RB 0.1595(0.0089)Aa 13.44(1.19)Aa 39.88(1.40)Ab

RW 0.1694(0.0083)Aa 13.89(1.09)Aa 38.20(1.22)Ab

61

4.2.2 Chrysanthemums leaf gas exchange in growth chamber

Figure 4.21 illustrates leaf responses of growth chamber grown plants tested under HPS

and different LED lights during LD and SD. During LD, leaf Pn (Fig.4.21 A) under all the light

sources showed a similar trend: continued to increase from 0 to 800 PAR and then, the

photosynthetic rate kept stable after 800 PAR light level. Leaf transpiration showed an increasing

trend under all light sources (Fig.4.21 C). The interesting point was that leaf transpiration under

HPS was the lowest compared to RB and RW at low light intensities. But it reached rates similar

to those under RB and RW at the 800 PAR light level and got to higher levels at the highest light

level. Leaf WUE (Fig. 4.21 E), had similar trend under all the tested light sources: kept increasing

from 0 to 800 PAR light level and then stayed stable. However, B light made plants have the lowest

WUE compared to the others light treatments. During SD, leaves tested under all lights showed a

similar trend in Pn (Fig.4.21 B), transpiration (Fig.4.21 D) and WUE (Fig.4.21 F). For Pn (Fig.4.21

B), there was a continual increase from 0 to 800 PAR and then it kept stable. For leaf transpiration

(Fig.4.21 D), there was a similar increasing trend among all tested light treatments. For WUE

(Fig.4.21 F), plants under all the light treatments showed similar trend as during LD.

When comparing LD and SD (Table 4.5), plants grown in the growth chamber had some

significant differences in some leaf physiological traits under specific lights. For example, leaves

had similar Rd during LD and SD under most light treatments, but leaves under RB and R had

higher Rd during LD than that during SD. Also, leaf LCP under RB, R and B light was higher

during LD. For Transpiration500 and WUE500, there were no significant differences between LD and

SD under each of the light treatment.

62

Figure 4.21: Light curves for leaf NCER, transpiration and WUE of growth chamber grown

chrysanthemums during LD (A, C and E) and SD (B, D and F). Plants were grown under the growth

chamber lights (fluorescent plus incandescent) but tested under HPS and different LED lights.

Every point represents the mean of at least 5 replicates ± SE.

X Data

0 200 400 600 800 1000 1200 1400

Leaf N

CE

R (

mol C

O2 m

-2 s

-1)

-5

0

5

10

15

20

25

X Data

0 200 400 600 800 1000 1200 1400

E (

mm

ol H

2O

m-2

s-1

)

0

1

2

3

4

5

Light intensity (mol m-2

s-1

)

0 200 400 600 800 1000 1200 1400 1600

WU

E (

mol C

O2 m

mol-1

H20)

0

5

10

15

X Data

0 200 400 600 800 1000 1200 1400

Leaf N

CE

R (

mol C

O2 m

-2 s

-1)

-5

0

5

10

15

20

25

30

X Data

0 200 400 600 800 1000 1200 1400

Tra

nspiration (

mm

ol H

2O

m-2

s-1

)

0

1

2

3

4

5

Light intensity (mol m-2

s-1

)

0 200 400 600 800 1000 1200 1400

WU

E (

mol C

O2 m

mol-1

H20)

0

5

10

15

HPS

RB

RW

R

B

W

A B

C D

E F

RB

RW

R

B

W

63

Figure 4.22: Leaf NCER light response curves of growth chamber grown chrysanthemums during LD (A) and SD (B) under different light sources.

The regression lines were calculated using the equation f = yo + a (1−e(−b*x)) and at least 5 replications for each light treatment.

light intensity (mol m-2

s-1

)

0 200 400 600 800 1000 1200 1400 1600

Ph

oto

syn

thetic r

ate

(

mo

l C

O2 m

-2 s

-1)

0

5

10

15

20

25

30

light intensity (mol m-2

s-1

)

0 200 400 600 800 1000 1200 1400

Lea

f N

CE

R (

mo

l C

O2 m

-2 s

-1)

0

5

10

15

20

25

30

HPS

RB

RW

R

B

W

RB

RW

R

B

W

A B

64

Table 4.5: A summary of the major physiological traits determined by analysis of leaf gas exchanges of growth chamber chrysanthemums during

LD and SD. Plants were grown under the growth chamber lights (fluorescent plus incandescent) but tested under HPS and different LED lights. The

Rd, LCP, YQ and Pnmax are calculated using the equation f = yo + a (1−e(−b*x)) while Pn500, Transpiration500, and WUE500 are values at 500 μmol m−2

s−1 PAR for each light treatment tested. All values represent the mean of at least 5 leaf replicates and with the standard error (±), shown in parentheses.

The leaf data for the SD condition under HPS was not available (NA) statistically at the time of submission of the thesis. Upper case letters (A, B,

C and D) represents statistical significances among the light treatments in the same photoperiod (LD or SD). Lower case letters (a, b) represent

statistical significances under the same light, between LD and SD. Statistical differences were determined by a one-way ANOVA with a Tukey’s-

Kramer adjustment (p<0.05).

65

light treatment Rd

(µmol m-2 s-1)

LCP

(µmol m-2 s-1) YQ

Pnmax

(µmol m-2 s-1) Pn500

(µmol m-2 s-1) Transpiration 500

(mmol H2O m-2 s-1)

WUE500

(µmolCO2/mmolH2O)

LD

HPS -1.51(0.09)A 24.36(1.93)A 0.064(0.001)A 31.25(1.59)A 18.40(0.44)A 2.14(0.12)A 8.67(0.33)Aa

W -1.82(0.12)Aa 26.71(1.91)Aa 0.071(0.001)Aa 28.56(0.69)ABa 18.17(0.34)Aa 2.35(0.12)Aa 7.82(0.40)Aa

RB -1.77(0.18)Ab 26.84(3.44)Aa 0.067(0.003)Aa 26.21(0.38)BCa 17.47(0.48)ABa 2.40(0.14)Aa 7.40(0.46)ABa

RW -1.39(0.21)Aa 22.66(3.68)Aa 0.065(0.001)Aa 23.63(1.23)CDa 17.01(0.56)ABa 2.32(0.21)Aa 7.58(0.51)Aa

R -1.59(0.13)Ab 28.20(1.74)Aa 0.055(0.001)Ba 26.40(0.90)BCa 15.96(0.65)Ba 1.85(0.14)Aa 8.80(0.48)Aa

B -1.39(0.11)Aa 28.80(2.38)Aa 0.049(0.001)Bb 21.05(0.46)Da 13.18(0.24)Cb 2.45(0.14)Aa 5.47(0.32)Ba

SD

HPS NA NA NA NA NA NA NA

W -1.59(0.12)Ba 25.39(1.98)Aa 0.062(0.007)Aa 23.08(1.54)Ab 16.88(1.36)Aa 2.34(0.39)Aa 8.26(1.35)Aa

RB -0.94(0.03)Aa 17.21(0.95)Ab 0.056(0.004)Aa 21.83(1.55)Ab 14.72(1.06)Aa 1.97(0.28)Aa 7.91(0.65)Aa

RW -0.92(0.11)Aa 20.10(1.98)Aa 0.049(0.004)Ab 25.99(2.14)Aa 14.91(0.41)Ab 1.90(0.18)Aa 8.09(0.53)Aa

R -1.09(0.13)ABa 22.89(1.37)Ab 0.049(0.006)Aa 26.61(0.92)Aa 14.73(1.25)Aa 2.13(0.28)Aa 7.24(0.54)Aa

B -0.99(0.16)Aa 17.96(2.90)Ab 0.056(0.001)Aa 20.08(0.42)Aa 14.06(0.22)Aa 2.97(0.19)Aa 4.81(0.29)Aa

66

5. Discussion

5.1 Whole plant diurnal patterns of gas exchange and growth during LD and SD

5.1.1 LD and SD under conventional HPS

Surprisingly, little is known regarding daily patterns of photosynthesis and water uptake at the

whole plant level in chrysanthemums, and how their growth and morphology during the LD

(vegetative) and SD (flowering) production cycles are influenced by HPS lighting. In our attempt

to fill these gaps in our knowledge, we grew the cultivar White Regan under both LD and SD

conditions in growth chambers under artificial lights and in the research greenhouse under natural

lighting conditions supplemented with HPS or different LED fixtures (Table 3.1). Under HPS,

whole plant NCER showed similar diurnal patterns when plants were grown in the greenhouse,

under natural lighting alone or supplemented with LEDs (Fig.4.5 A and B; Fig.4.9 A and B) and in

the growth chambers (Fig.4.17 A and B). Whole plant photosynthesis during LD and SD were

steady throughout the daytime. At night, the respiration rate of these plants was also steady during

both the LD and the SD growth phases. Since the daily patterns of gas exchange remained relatively

steady during daytime and nighttime periods, we averaged photosynthesis and respiration rate and

compared these on the bases of different anatomical physiological parameters (Fig.4.10 and 4.18).

In both LD and SD plants, the larger, flowering plants exchanged more carbon (panel A vs panel

B) in the light and dark on the plant basis. However, when photosynthesis and respiration were

expressed on either the dry weight basis (panel C and D) or the leaf area basis (panel E and F), the

LD, vegetative plants exchanged more carbon than did the SD plants. When photosynthesis and

respiration were integrated (i.e., added) for the full 24-hour daily cycle to calculate daily carbon

gain (Fig.4.11 and 4.19), the plants during their SD production period grew more on a plant basis

under all lighting conditions, and less on a dry weight or leaf area basis. Interestingly, when

expressed in the leaf area basis, the plants supplemented with HPS in both the LD and SD

photoperiod, had slightly faster growth rate than the two LEDs (RB and RW; panel E and F).

The transpiration rate of chrysanthemum plants grown both in the research greenhouse

(Fig.4.9 C and D) and in the growth chamber (Fig.4.17 C and D) showed similar diurnal patterns

under HPS during LD and SD developmental periods. Transpiration followed a well-known pattern

with many herbaceous plants, where stomata tend to close at night thus reducing the transpiration

rate at nighttime relative the daytime. After getting the average, both the greenhouse (Fig.4.12 A

and B) and growth chamber (Fig.4.20 A and B) grown plants showed more transpiration rate during

LD than SD. This is consistent with the fact that most leaves of a plant during LD (smaller plants/

67

open canopy) face higher light intensities and will have higher transpiration rates compared to those

of leaves on a plant during SD having a denser canopy and therefore more mutual shading.

For WUE, chrysanthemums grown both in the greenhouse (Fig.4.9 E and F) and the growth

chamber (Fig.4.17 E and F) showed similar patterns under HPS during LD and SD. This pattern

was the result of changing transpiration rates over the daytime rather than changes in

photosynthesis. However, for the average value, plants grown in the greenhouse showed no

significant difference between LD and SD, while plants grown in the growth chamber illustrated

higher WUE value during SD than LD.

5.1.2 LD and SD under newer LED systems

Under the LED lighting systems, plants also showed similar diurnal pattern of NCER to that

under HPS during LD and SD. During LD and SD, plants had steady photosynthesis rates at

daytime and steady respiration rates at nighttime in both research greenhouse (Fig.4.9 A and B)

and growth chamber (Fig.4.17 A and B). The average photosynthesis and respiration rates were

also calculated on the different bases (Fig.4.10 and 4.18). What the data showed is that plants grown

under the LEDs have similar comparison between LD and SD to that under the HPS.

Chrysanthemums grown under the LEDs also exhibited similar daily carbon gain (Fig.4.11 and

4.19) to that under the HPS. All the supplemental lights enhanced biomass of chrysanthemums

(Fig.4.4), especially the RB. It has also been proved the mixed RB LED enhanced the plant growth

by increasing the dry and fresh matter, comparing to the monochromic LEDs (Nhut et al., 2000;

Lian et al., 2002; Poudel et al., 2008; Shin et al., 2008). What we found supports Kim et al. (2004)

results. The RB produced the greatest enhancement effect in terms of leaf area, dry matter and

chlorophyll content. Combination of R and B LEDs are thought to be effective for growing

numerous plants such as spinach, radish, lettuce, wheat and rice (Yorio et al., 2001; Goins et al.,

1997; Matsuda et al., 2004).

It seems that there was a similar diurnal pattern shown in both transpiration and WUE of the

chrysanthemums (Fig.4.9 and 4.17) under LEDs and HPS during LD and SD. In all cases, the

stomata could be responsible for these two parameters. The result showed that stomata follow a

certain circadian rhythm under all the supplemental light, which goes upwards and down for

transpiration and downwards and up for WUE. What we found support McClung (2006), who said

that plants could have circadian rhythms under the light. There are many processes of plants that

follow a circadian rhythm, such as general growth, gas exchange and stomatal movement

(Cumming and Wagner, 1968; McClung and Kay, 1994). Toth et al. (2001), found that the

68

cryptochrome (CRY) proteins of Arabidopsis seedings showed the increase pattern of expression

level after the light was turned on and then went downwards. Also, the Arabidopsis cry1 cry2

mutants showed a decrease stoma opening when exposed to B light, which indicates the strong

relationship between CRY and stomata opening (Mao et al., 2005). The diurnal pattern we got for

transpiration (Fig. 4.5, 4.9 and 4.17) is very close to that of CRY shown by Toth et al. (2001) and

in Dodd et al. (2004). Thus, what we found in the transpiration pattern may be due to the function

of CRY. Liu et al. (2011) showed that tomato plants grown under high amounts of B lights had the

increased stomatal aperture and more stomata. Although, there are no previous reports for

chrysanthemum leaf transpiration due to effects of LEDs on stomata, it is possible that the decrease

WUE of the two LED supplemental lights are due to the difference of stomata which is caused by

the B component of the light.

Chrysanthemums under LEDs had a higher average transpiration during LD than SD in both

greenhouse (Fig.4.12 A and B) and growth chamber (Fig.4.20 A and B), which was similar to that

of HPS. However, in terms of daytime average WUE, the comparisons between LD and SD were

not same between greenhouse and growth chamber grown plants. It seems that chrysanthemums

responded to the light quality differently between long-term acclimation and short-term exposure

condition.

In general, chrysanthemums showed little or no significant difference in terms of NCER

among the supplemental light treatments (Fig.4.5, 4.9 and 4.17). But, there were differences in both

diurnal pattern (Fig.4.5, 4.9 and 4.17) and daily averages (Fig.4.6, 4.8, 4.10, 4.12, 4.18 and 4.20)

in terms of both transpiration and WUE. Thus, different supplemental lights can affect the

transpiration and WUE of chrysanthemums without major changes in the whole plant NCER during

the same photoperiod. Taken together, our data indicate that the spectrum of light can influence the

stomata and their function but not change the primary photosynthesis. Studies suggest that plant

grown under supplemental light could have changed whole plant and leaf morphologies (Gay and

Hurd, 1975; Goins et al., 1997; Liu et al., 2011, 2012; Rabara et al., 2017).

During the winter, greenhouse production has not only the lights but also the lower humidity

as the limiting factors. These environmental conditions cause stomata to keep in a close state (Lange

et al., 1971). The closure of stomata will result in reduced transpiration of the whole plant, which

can alter uptake of essential micronutrients which are important to many physiological and

biochemical process (Xu et al., 2000; Baligar et al., 2001; Rouphael and Colla, 2005; Alloway,

2008). Based on our result, utilization of the RB and RW LED can help plant regulate micronutrient

69

uptake indirectly under stress condition due to the effect of spectral quality to affect stomatal

opening and increase the transpiration rate.

5.2 Leaf gas exchange during LD and SD

There has been a lot of research using filtered white light and recently LEDs, to help

researchers to determine the photosynthetic response of leaves to spectrum specific lighting

(McCree, 1971; Goins et al., 1997; Sun et al., 1998; Hogewoning et al., 2010; Liu et al., 2009).

However, most of the studies use plants grown under the light of interest, which means they are

using the long-term acclimated plants. Because of that, the difference in leaf behavior may be due

to the different morphological characteristics, such as leaf area and leaf thickness (Brazaityte et al.,

2010; Liu et al., 2011, 2012). Therefore, we should design both short-term and long-term exposure

leaf experiments.

The data shown in Figure 4.21, 4.22 and Table 4.5 represent the plants grown under the white

light and tested under a short-term exposure. That is the comparison of similar leaves and how they

react to the short-term light exposure. Generally, plants responded to the light quality differently

between LD and SD (Table 4.5). During LD, there were a lot differences among all the light

treatment in photosynthesis. While during SD, there was no or little difference among all the light

treatments in all the leaf parameters. Therefore, light quality has a stronger effect in leaves during

LD than SD. Interestingly, in terms of transpiration and WUE, chrysanthemums had a similar

response to the light quality during LD and SD, which means what we found about different effects

of light quality at the leaf level between LD and SD was not due to the stomata function.

The data shown in Table 4.3 represent the plants grown under the three supplemental lights

and tested under Licor-6400 RB light. That is the comparison of long-term exposure leaves and

how they react to the same light. Most physiological parameters under different supplemental light

were similar during the two photoperiods (i.e., LD or SD). Comparing what I got to Zhou et al.

(2013) who studied the cultivar Reagan, our values of Pnmax were similar. However, the Rd that we

measured for cv. White Reagan was much lower than they reported. The lower Rd we measured

helps explain the lower LCP.

5.3 Summary and implications

In our experiments, we took the whole plant measurements of chrysanthemum during both LD

and SD. Thus, we have a comparison of different development stages, which is not seen in any

other previous studies. Generally saying, RB and RB LED supplemental lights produced

70

chrysanthemums of similar commercial quality to those growing under HPS and provided the

similar photosynthetically active radiation during both LD and SD production cycle comparing to

conventional HPS. Taken together, the data from our research greenhouse and chrysanthemums

grown at our commercial partner (Slaman Greenhouses) showed that cut flowers were of similar

commercial quality under HPS and the two LED light systems (i.e., RB and RW). Interestingly,

however, the RB LED produced cut flowers over the 7 to 8 week period almost 4 to 6 days earlier

than did the HPS or RW. The economic value of the slightly shorter production period merits

further study.

At the whole plant level, we saw similar results from both the research greenhouse and growth

chamber chrysanthemums. For NCER (Fig.4.10 and 4.18), chrysanthemums showed a lower

photosynthesis and respiration during LD than SD on per plant basis. But on dry weigh and leaf

area basis, plants during LD had higher photosynthesis and respiration rates than SD. For

transpiration (Fig.4.12 and 4.20), plants presented a higher transpiration during LD than SD. These

results above were observed in both research greenhouse and growth chamber plants among all the

supplemental light treatments, which indicated that the differences were not due to the light quality

or short-term light exposure. However, the WUE results showed a little difference (Fig.4.12 and

4.20). Plants grown in the research greenhouse had a higher WUE during LD than SD, under the

two LED light but not HPS. In contrast, plants grown in the growth chamber had a lower WUE

during LD than SD among all the three supplemental light treatments. In conclusion, at the whole

plant level, LEDs and HPS had similar effect in terms of photosynthesis and respiration but differed

in terms of water exchange and stomatal function.

At the leaf level, under the LD condition, Pnmax and Pn500 were statistically different depending

on the light quality (Table 4.5). Interestingly, under the SD condition, mature leaves had similar

photosynthesis rates at both light levels among the different wavelength tested. It was interesting

that during the vegetative stage chrysanthemums had a sensitive response to light quality but

became monotonous with respect to spectral quality when they were supporting flower stage (Table

4.5). The leaf NCER (i.e., photosynthesis) were greater during LD than SD, but this difference was

probably not due to the difference in stomata function since the transpiration rates were similar

under all lights between LD and SD. We have no mechanistic explanation for the apparent

sensitivity of the leaves of LD (vegetative) plants vs insensitivity of the SD (flowering) plants to

spectral quality. Although an explanation for this observation is not clear at this moment, the data

with chrysanthemums as an important Canadian commercial crop indicates that more work is

71

required to optimise the light quality for different plant stages during the greenhouse production

cycle of other flowering crops.

72

Reference

Alloway, B. J. (Ed.). (2008). Micronutrient Deficiencies in Global Crop Production. Springer

Science & Business Media.

Baligar, V. C., Fageria, N. K., and He, Z. L. (2001). Nutrient use efficiency in plants. Commun.

Soil Sci. Plant Anal. 32, 921–950.

Bourget, C. M. (2008). An introduction to light-emitting diodes. HortScience, 43(7), 1944-1946.

Brazaityte, A., Duchovskis, P., Urbonaviciute, A., Samouliene, G., Jankauskiene, J.,

Sakalauskaite, J., et al. (2010). The effect of light-emitting diodes lighting on the growth

of tomato transplants. Zamdirbyste Agric. 97, 89–98.

Cumming, B. G., and Wagner, E. (1968). Rhythmic processes in plants. Annu. Rev. Plant.

Physiol. 19, 381–416.

Davis, S. D., and McCree, K. J. (1978). Photosynthetic rate and diffusion conductance as a

function of age in leaves of bean plants. Crop Sci. 18, 280–282.

De Vries, F. W. T. P. (1982). Phases of development of models. Centre of Agricultural

Publishing and Documentation (Pudoc), 20–25.

Dodd, A. N., Parkinson, K., and Webb, A. A. R. (2004). Independent circadian regulation of

assimilation and stomatal conductance in the ztl-1 mutant of Arabidopsis. New Phytol.,

164, 63–70.

Dutton, R. G., Jiao, J., Tsujita, M. J., and Grodzinski, B. (1988). Whole-plant CO2 exchange

measurements for non-destructive estimation of growth. Plant Physiol. 86, 355–358.

Fukui, H., Yu, W., Uno, H., Kobayashi, N., and Sasaki, O. (2009). Effect of red LED lamp with

wavelength of 660 nm on floral bud differentiation of Chrysanthemum. In VI

International Symposium on Light in Horticulture 907, 319-322.

Gay, A. P., and Hurd, R. G. (1975). The influence of light on stomatal density in the tomato. New

Phytol. 75, 37–46.

Goins, G. D., Yorio N. C., Sanwo, M. M., and Brown, C. S. (1997). Photomorphogenesis,

photosynthesis, and seed yield of wheat plants grown under red light-emitting diodes

(LEDs) with and without supplemental blue lighting. J. Exp. Bot., 48, 1407-1413.

73

Higuchi, Y., Sumitomo, K., Oda, A., Shimizu, H., and Hisamatsu, T. (2012). Day light quality

affects the night-break response in the short-day plant chrysanthemum, suggesting

differential phytochrome-mediated regulation of flowering. Journal of plant physiology,

169(18), 1789-1796.

Hogewoning, S. W., Trouwborst, G., Maljaars, H., Poorter, H., van Ieperen, W., and Harbinson,

J. (2010). Blue light dose-responses of leaf photosynthesis, morphology, and chemical

composition of Cucumis sativus grown under different combinations of red and blue

light. J. Exp. Bot. 61, 3107–3117.

Huan, Z., ZhiGang, X., Jin, C., AiSu, G., and YinSheng, G. (2010). Effects of light spectral

energy distribution on multiplication and rooting of chrysanthemum plantlets in vitro.

Acta Horticulturae Sinica, 37(10), 1629-1636.

Jeong, S. W., Hogewoning, S. W., and van Ieperen, W. (2014). Responses of supplemental blue

light on flowering and stem extension growth of cut chrysanthemum. Scientia

Horticulturae, 165, 69-74.

Jeong, S. W., Park, S., Jin, J. S., Seo, O. N., Kim, G. S., Kim, Y. H., ... and Shin, S. C. (2012).

Influences of four different light-emitting diode lights on flowering and polyphenol

variations in the leaves of chrysanthemum (Chrysanthemum morifolium). Journal of

agricultural and food chemistry, 60(39), 9793-9800.

Kim, H. H., Goins, G. D., Wheeler, R. M., and Sager, J. C. (2004a). Stomatal conductance of

lettuce grown under or exposed to different light qualities. Ann. Bot. 94, 691–697.

Kim, H. H., Goins, G. D., Wheeler, R. M., and Sager, J. C. (2004b). Greenlight supplementation

for enhanced lettuce growth under red- and blue-light-emitting diodes. Hortscience 39,

1617–1622.

Kim, S. J., Hahn, E. J., Heo, J. W., and Paek, K. Y. (2004). Effects of LEDs on net photosynthetic

rate, growth and leaf stomata of chrysanthemum plantlets in vitro. Scientia Horticulturae,

101(1), 143-151.

Kurilčik, A., Dapkūnienė, S., Kurilčik, G., Duchovskis, P., Urbonavičiūtė, A., Žilinskaitė, S., and

Žukauskas, A. (2011). Effect of far-red light on the growth of chrysanthemum plantlets in

vitro. Sodininkystė ir daržininkystė, 103.

74

Lange, O. J., Losch, R., Schulze, E. D., and Kappen, L. (1971). Responses of stomata to changes

in humidity. Planta, 100, 76–86.

Lanoue, J., Leonardos, E. D., Ma, X., and Grodzinski, B. (2017). The effect of spectral quality on

daily patterns of gas exchange, biomass gain, and water-use-efficiency in tomatoes and

lisianthus: An assessment of whole plant measurements. Frontiers in plant science, 8,

1076.

Leonardos, E. D., Rauf, S. A., Weraduwage, S. M., Marillia, E. F., Taylor, D. C., Micallef, B. J.,

et al. (2014). Photosynthetic capacity of the inflorescence is a major contributor to daily-

C-gain and the responsiveness of growth to elevated CO2 in Arabidopsis thaliana with

repressed expression of mitochondrial-pyruvate-dehydrogenase-kinase. Environ. Exp.

Bot. 107, 84–97.

Lian M. L., Murthy H. N., Paek K. Y. (2002) Effects of light emitting diodes (LED) on the in

vitro induction and growth of bulblets of Lilium oriental hybrid ‘Pesaro’. Sci Hortic 94,

365–370

Liu, X. Y., Chang, T. T., Guo, S. R., Xu, Z. G., and Li, J. (2009). Effect of different light quality

of LED on growth and photosynthetic character in cherry tomato seedlings. Acta. Hortic.

907, 325–330.

Liu, X. Y., Gou, S. R., Xu, Z. G., Jiao, X. L., and Tezuka, T. (2011). Regulation of chloroplast

ultrastructure, cross-section anatomy of leaves, and morphology of stomata of cherry

tomato by different light irradiations of light-emitting diodes. Hortscience, 46, 217–221.

Liu, X. Y., Guo, S. R., Chang, T. T., Xu, Z., and Tezuka, T. (2012). Regulation of the growth and

photosynthesis of cherry tomato seedlings by different light irradiations of light emitting

diodes (LED). Afr. J. Biotechnol., 11, 6169–6177.

Lund, J. B., Blom, T. J., and Aaslyng, J. M. (2007). End-of-day lighting with different red/far-red

ratios using light-emitting diodes affects plant growth of Chrysanthemum× morifolium

Ramat.‘Coral Charm’. HortScience, 42(7), 1609-1611.

Mao, J., Zhang, Y. C., Sang, Y., Li, Q. H., and Yang, H. Q. (2005). A role of Arabidposis

cryptochromes and COP1 in the regulation of stomatal opening. Proc. Natl. Acad. Sci.,

102, 12270–12275.

75

Matsuda, R., Ohashi-Kaneko, K., Fujiwara, K., Goto, E., and Kurata, K. (2004). Photosynthetic

characteristics of rice leaves grown under red light with or without supplemental blue

light. Plant cell Physiol., 45, 1870-1874.

McClung, R. J. (2006). Plant circadian rhythms. Plant Cell, 18, 792–803.

McClung, R. J., and Kay, S. A. (1994). Circadian rhythms in Arabidopsis thaliana. Cold Spring

Harbor Monograph Series, 27, 615-615.

McCree, K. J. (1971). The action spectrum, absoprtance and quantum yield of photosynthesis in

crop plants. Agric. Meterol., 9, 191–216.

Miler, N., and Zalewska, M. (2004). The influence of light colour on micropropagation of

chrysanthemum. In V International Symposium on In Vitro Culture and Horticultural

Breeding 725, 347-350.

Nakamura, S., Mukai, T., and Senoh, M. (1994). Candela-class high-brightness InGaN/AlGaN

double-heterostructure blue-light-emitting diodes. Appl. Phys. Lett. 64(13), 1687–1689.

Nelson, J. A., and Bugbee, B. (2014). Economic analysis of greenhouse lighting: light emitting

diodes vs. High intensity discharge fixtures. PLoS ONE 9(6), e99010.

Nhut, D.T., Hong, L.T.A., Watanabe, H., Goi, M., Tanaka, M. (2000) Growth of banana plantlets

cultured in vitro under red and blue lightemitting diode (LED) irradiation source. In

International Symposium on Tropical and Subtropical Fruits 575, 117-124.

Poudel, R. P., Kataoka, I., Mochioka, R. (2008) Effect of red-and bluelightemitting diodes on

growth and morphogenesis of grapes. Plant Cell Tissue Organ Cult 92, 147–153

Rabara, R. C., Behrman, G., Timbol, T., and Rushton, P. J. (2017). Effects of spectral quality of

monochromatic LED lights on the growth of artichoke seedlings. Front. Plant Sci. 8, 190.

Rouphael, Y., and Colla, G. (2005). Growth, yield, fruit quality and nutrient uptake of

hydrophonically cultivated zucchini squash as affected by irrigation systems and growing

seasons. Sci. Hortic. 105, 177–195.

Runkle, E. S., and Heins, R. D. (2001). Specific functions of red, far red, and blue light in

flowering and stem extension of long-day plants. J. Am. Soc. Hort. Sci. 126, 275–282.

76

Shimizu, H., Ma, Z., Tazawa, S., Douzono, M., Runkle, E. S., and Heins, R. D. (2005). Blue light

inhibits stem elongation of chrysanthemum. In V International Symposium on Artificial

Lighting in Horticulture, 711, 363-368.

Shin, S. K., Murthy, N. H., Heo, W. J., Hahn, J. E., Paek, Y. K. (2008) The effect of light quality

on the growth and development of in vitro cultured Doritaenopsis plants. Acta Physiol

Plantae, 30, 339–343

Sun, J., Nishio, J. N., and Vogelmann, T. C. (1998). Green light drives CO2 fixation deep within

leaves. Plant Cell Physiol. 39, 1020–1026.

Tepperman, J. M., Hudson, M. E., Khanna, R., Zhu, T., Chang, S. H., Wang, X., et al. (2004).

Expression profiling of phyB mutant demonstrates substantial contribution of other

phytochromes to redlight-regulated gene expression during de-etiolation. Plant J. 38,

725–739.

Toth, R., Kevei, E., Hall, A., Millar, A. J., Nagy, F., and Kozma-Bognar, L. (2001). Circadian

clock-regulated expression of phytochrome and cryptochrome genes in Arabidopsis.

Plant Physiol., 127, 1607–1616.

Van Ieperen, W., and Trouwborst, G. (2007). The application of LEDs as assimilation light

source in greenhouse horticulture: a simulation study. In International Symposium on

High Technology for Greenhouse System Management: Greensys2007, 801, 1407-1414.

Xu, G., Magen, H., Tarchitzky, J., and Kafkaf, U. (2000). Advances in chloride nutrition of

plants. Adv. Agron. 28, 97–150.

Yorio, N. C., Goins, G. D., and Kagie, H.R. (2001). Improving spinach, radish, and lettuce

growth under red light-emitting diodes (LEDs) with blue light supplementation.

HortScience, 36, 380-383.

Zhou, H., Yu, Q., Kuang, Q., Wang, W., Wang, F., and Xu, H. L. (2013). Light response of cut-

flower Chrysanthemum cultivars. Journal of Food, Agriculture & Environment, 11(1),

865-867.

77

Appendix

Figure 1: Commercial greenhouse chrysanthemums vs Research greenhouse chrysanthemums

final height. Every bar shows the mean of 10 plants ± standard error under different light treatments.

Upper case (A, B and C) represent statistic differences in the same location (Commercial or

Research greenhouse), across the light treatments. Lower case (a,b) represent the statistic

differences in the same light treatment, between Commercial and Research greenhouse.

Amb HPS RB RW

Heig

ht (m

)

0.0

0.2

0.4

0.6

0.8

1.0

Commerical Greenhouse

E2 Greenhouse

Ba

Aa Aa Aa

Cb

Aa

BbBb

The final height of commercial greenhouse chrysanthemums (black bar in Figure) illustrated

the distinguish results among different light condition. HPS got the highest, followed by 2 LEDs

(RB and RW), and Amb was the last. The final height of research greenhouse chrysanthemums

(grey bar in Figure) showed closer results among different light condition. All 3 supplemental light

treatments increased the height of the plants compared to the ambient grown plants. But there is no

significant difference between the HPS and two types of LEDs, which illustrated that HPS, RB and

78

RW had the similar enhanced effect in plants height. Moreover, the comparison between the same

light treatment in different location showed that the heights of research greenhouse

chrysanthemums were bigger (Amb, RB and RW) or equal (HPS) to those of commercial

greenhouse.

79

Figure 2: Commercial greenhouse chrysanthemums vs research greenhouse chrysanthemums final

SPAD reading. Every bar shows the mean of 10 plants ± standard error under different light

treatments. Upper case (A, B and C) represent statistic differences in the same location

(Commercial or Research greenhouse), across the light treatments. Lower case (a,b) represent the

statistic differences in the same light treatment, between Commercial and Research greenhouse.

Amb HPS RB RW

SP

AD

readin

g

0

20

40

60

80

Commercial Greenhouse

E2 Greenhouse

BbBb

Ab Ab

Ba

Aa

Ba Ba

The SPAD reading of commercial greenhouse got the similar results among different light

treatments and there were significant differences between 2 LED light treatments and HPS and

Amb. Plants under both RB and RW got the higher SPAD reading than those under HPS and Amb.

The SPAD reading of research greenhouse showed that HPS got a higher result than those of RB,

RW and Amb. The comparison between the same light treatments in different locations showed the

80

significant difference, which the results of research greenhouse were higher than those of

commercial greenhouse.