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For Review Only

Response of Growth, Yield and Quality of Pea Shoots to

Supplemental LED Lighting during Winter Greenhouse Production

Journal: Canadian Journal of Plant Science

Manuscript ID CJPS-2017-0276.R2

Manuscript Type: Article

Date Submitted by the Author: 12-Dec-2017

Complete List of Authors: Kong, Yun; University of Guelph, School of Environmental Sciences

Llewellyn, Dave; University of Guelph, Environmental Science Zheng, Youbin; University of Guelph, School of Environmental Sciences

Keywords: Pisum sativum L., cumulative yield, product quality, plant growth, light-emitting diodes

https://mc.manuscriptcentral.com/cjps-pubs

Canadian Journal of Plant Science

For Review Only

Response of Growth, Yield and Quality of Pea Shoots to Supplemental LED

Lighting during Winter Greenhouse Production

Yun Kong, Dave Llewellyn and Youbin Zheng1

School of Environmental Sciences, University of Guelph, 50 Stone Road East, Guelph,

Ontario N1G 2W1, Canada

1Corresponding author (e-mail: [email protected])

Abstract: Low natural light levels during winter months is a major limiting factor for

greenhouse production in northern regions. To determine the effects of supplemental

lighting (SL) on winter greenhouse production of pea shoots, crop growth, yield and

quality were investigated under the treatments of supplemental photosynthetic photon

flux density (PPFD) of 50, 80, 110, and 140 µmol·m-2·s-1, all with a 16-h photoperiod,

plus a no SL control treatment, inside a Canadian greenhouse from December to March.

Light-emitting diodes with red/blue PPFD ratio of 4:1 and peak wavelengths at 665 nm

and 440 nm were used for the lighting treatment. During the trial period, the average

natural daily light integral (DLI) inside the greenhouse was 5.3 mol·m-2·d-1, and average

daily temperature was around 13℃. Compared to the no SL control, SL of 50–140

µmol·m-2·s-1 increased stem length and leaf number before the first harvest, and

promoted cumulative yield (kg·m-2) of pea shoots throughout the five harvest times.

Total yield (kg·m-2) of five harvests and weekly average stem extension rate were

proportional to supplemental PPFD within the range of 0–140 µmol·m-2·s-1. However,

SL of 50–80 µmol·m-2·s-1, corresponding to total (natural + supplemental) DLI of

8.1–9.8 mol·m-2·d-1, resulted in the best integrated quality based on evaluation of

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individual fresh mass, soluble solids content, succulence, and firmness. Therefore, a

total DLI ranging between 8.1 and 9.8 mol·m-2·d-1 can be suggested as a target for

winter greenhouse production of pea shoots under conditions similar to this trial.

Key words. Pisum sativum L., cumulative yield, product quality, plant growth,

light-emitting diodes.

Introduction

Pea shoots, the young, tender vine tips of snow peas (Pisum sativum L.), are

recognized as a popular specialty vegetable in Asia and Africa (Lim 2012). They are

served fresh, lightly steamed or sautéed, and are prepared alone or as an attractive

edible garnish (Miles and Sonde 2003). Pea shoots have become an increasingly

popular part of a healthy diet worldwide, due partially to their richness in

health-promoting phytochemicals, especially antioxidants such as vitamin C,

carotenoids and phenolic compounds (Liu et al. 2014; Santos et al. 2014).

In northern-climate regions like Ontario, Canada, pea shoots may be an alternative

locally-produced commodity during winter for greenhouse vegetable growers, who face

decreasing profit margins due to intense price competition with imported produce and

increased energy costs (Hendricks 2012). With optimum production temperatures of

13–18 °C (Miles and Sonde 2003), pea shoots can be grown in greenhouses during the

colder months, with low heating-energy inputs relative to other common

greenhouse-grown vegetable commodities (e.g., tomatoes, cucumbers and peppers).

Local production is ideal for pea shoots as their tender nature makes them unsuitable

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for long distance transportation. Also, with proper crop management, pea shoots can be

harvested many times throughout a single production cycle (Miles and Sonde 2003).

The low natural light level during winter months is a major limiting factor in

greenhouse vegetable production in northern regions such as Canada (Demers and

Gosselin 2002). In southern Canada, as well as northern U.S., outdoor solar daily light

integrals (DLI) during winter (especially November through January) are often below

10 mol·m-2·d-1 (Demers et al. 1998; Korczynski et al. 2002; Dorais 2003), which can be

further reduced by 30% to 60% inside a greenhouse due to losses through covering

materials, supporting structures and other opaque infrastructure (Critten 1993;

Giacomelli and Roberts 1993; Zhang 2001; Llewellyn et al. 2013). On an average

December day, the amount of PAR (photosynthetically active radiation) available inside

greenhouses located in Vancouver (British Columbia), Montréal (Quebec), and Harrow

(Ontario) ranged from 0.5 to 1.0 MJ·m-2·d-1 (≈ 2.3 to 4.6 mol·m-2·d-1), assuming that

PAR represents 42% of global light energy and that 50% of PAR is transmitted into the

greenhouse (Papadopoulos et al. 2002). Thus, without supplemental lighting (SL), there

is very little greenhouse production during the two to three darkest months (i.e.,

December through February) in Canada (Papadopoulos et al. 2002). Accordingly, SL is

a very useful tool to promote greenhouse crop production during the low light months

in these regions (Dorais 2003). High pressure sodium (HPS) lamps have been

commonly used as a SL source in higher latitudes (Hemming 2011). Recent

developments in light-emitting diode (LED) technologies have given rise to

horticultural LEDs which are being increasingly used for greenhouse crop production

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(Morrow 2008; Hao et al. 2015; Zheng 2016). LED-based lighting systems have a

number of advantages over traditional HPS lamp, which include, for example, high

energy saving due to the ability to control spectral output for maximum production

without wasting energy on nonproductive wavelengths, as well as the ability to

dynamically control light level based on available solar light if integrating related

sensors (Morrow 2008; Zheng 2016). Many current horticultural LED technologies

focus on producing red and blue light as these two wavelengths are known to be readily

absorbed and utilized for photosynthesis by the leaves of most plants (McCree 1971).

Also, it has been reported that the combination of red and blue LED light is an effective

SL source for the production of many crops, with similar or even higher energy

efficiency compared to HPS lamps (Lu et al. 2012; Olle and Virsile 2013; Nelson and

Bugbee 2014; Choi et al. 2015; Mitchell et al. 2015; Singh et al. 2015; Wojciechowska

et al. 2015; Poel and Runkle 2017).

It was suggested that SL might be necessary for pea shoot production in

greenhouses from November through March at higher latitudes (Miles and Sonde 2003).

Clarifying SL effects on growth, yield and quality in pea shoots and identifying optimal

light levels during winter production will provide useful information to greenhouse

growers in these regions. However, there is little related information available on this

commodity in the literature. Further, while there are studies related to SL HPS light

levels on other crops, it has so far been difficult to find the reports on responses of

greenhouse plants to varied levels of SL from LEDs (Olle and Virsile 2013; Singh et al.

2015). Studies in Quebec during the winter indicated that supplemental HPS lighting

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with a PPFD of 50–100 µmol·m-2·s-1 over a 16-h photoperiod increased lettuce biomass

production by 40%, reduced the time to harvest by 25%, and improved harvest quality

such as heart firmness, compared to natural light only (Gaudreau et al. 1994). For

greenhouse production of various vegetables in Quebec during mid-November to

mid-February, different PPFD levels of SL using HPS lamps for a photoperiod of 12 to

16 h have been recommended: 50 to 100 µmol·m-2·s-1 for lettuce, 100 to 150

µmol·m-2·s-1 for tomato, 120 to 150 µmol·m-2·s-1 for cucumber, and 150 to 175

µmol·m-2·s-1 for sweet pepper (Dorais 2003). For indoor production of pea microgreens

in China, 35–100 µmol·m-2·s-1 PPFD for 12 to16-h has been recommended as optimal

SL intensity range when using fluorescent lamps, because lower PPFD can result in

yellow leaves, slender and weak stems, while higher light levels can induce too high

fiber content and reduce shoot tenderness (Zhang and Hu 2008). Contrasting to pea

shoots, pea microgreens are normally grown indoors at a higher temperature (20–25℃)

and have a much shorter production time (i.e. 10–14 d) (Zhang and Hu 2008). It is clear

that SL effects and recommended lighting levels vary with crop species, lamp type,

production location and other growth factors.

The light intensity supplied by commercial greenhouse SL is usually not higher than

200 µmol·m-2·s-1 due to economic considerations (Both 2000), and a typical PPFD of SL

provided to high-light fruit vegetable crops is around 150 µmol·m-2·s-1, with lower SL

light levels (e.g., 50–100 µmol·m-2·s-1) for leafy vegetables (Dorais 2003; Runkle 2011).

Although peas have been classified as plants with high-light demand, they have a strong

ability to acclimate to varied growth light conditions (Bethlenfalvay and Phillips 1977;

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Chow and Anderson 1987). Also, pea shoots are produced as leafy vegetables, so their

production may be suited to SL intensities lower than 150 µmol·m-2·s-1. Peas are

day-neutral plants and new shoots (vs. pods) are the harvested parts for pea shoot

production, so there should be no specific photoperiod requirement for production. In

practice, greenhouse vegetable growers generally use photoperiods of 14–17 h (Demers

and Gosselin 1999) during the SL season. However, the duration of SL is limited to

maximum of 16 h for leafy vegetables, in order to avoid tipburn (Papadopoulos et al.

2002). It appeared that the optimal SL level for pea shoot production might be within a

range of between 0–150 µmol·m-2·s-1 if using a 16-h photoperiod.

Taking all the above information into account, it was hypothesized: (1) SL using

LED vs. no SL can promote growth, yield, and some quality traits of pea shoots during

winter greenhouse production in northern regions; (2) different quality traits (e.g. size

vs. firmness) in pea shoots respond differently to increased light level of SL; (3) within

a range of SL intensities of 0–150 µmol·m-2·s-1, if using a ≤16-h photoperiod, there is an

optimal light level for winter production of pea shoots, based on different responses in

growth, yield, and quality.

The objective of the present study was to elucidate the target light level for

greenhouse production of pea shoots during winter months in Southern Ontario and

regions with similar latitudes by testing the above hypothesis.

MATERIALS AND METHODS

Plant materials and growing conditions

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The experiment was conducted in the Edmund C. Bovey Building Research

Greenhouse Complex at the University of Guelph, Guelph, ON, Canada (Lat. 43°33´N,

Long. 80°15´W). Seeds of snow pea ‘Zhongnong 6’ (AgroHaitai Ltd., Ontario, Canada)

were sown in 5 cm × 5 cm × 6 cm cell containers using a peat-based substrate (Seeding

Mix, Premier Tech, Rivière-du-Loup, Quebec, Canada) on 18 Dec 2014. The sowed

seeds were kept at 22/20 °C (day/night) to promote germination. Six days after sowing,

germinated seeds were transferred to the greenhouse bench under supplemental LED

lighting, and lighting treatments were initiated at this stage. The temperature was set at

14/12 ºC (day/night), and relative humidity at 65%. Beginning 27 d after the start of

treatment, pea shoots were harvested below the first upper fully expanded leaf every 10

to 14 d, until open flowers were present in more than 50% of the plants. Plants were

alternately subirrigated once or twice each week with tap water (EC ≈ 0.8 dS·m-1, pH ≈

7.5) or nutrient solution (EC ≈ 2.6 dS·m-1, pH ≈ 6.5). The nutrient solution was made

from tap water and 20–8–20 water soluble fertilizer (Plant Products Inc., Brampton,

Ontario, Canada) with a mass ratio of 800:1. The solution had the following nutrients

(mg·L–1): 250.0 nitrogen, 42.5 phosphorus, 207.5 potassium, 184.0 calcium, 1.9

magnesium, 0.6 copper, 0.3 boron, 0.6 manganese, 0.6 zinc, 0.2 molybdenum, and 1.3

iron. The climate data was logged using an Argus weather station (Argus Control

Systems Ltd., British Columbia, Canada) that controlled the greenhouse environment,

and the natural light conditions, air temperature and relative humidity inside the trial

greenhouse are presented in Fig. 1.

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Lighting treatments and experimental design

Plants were grown under natural light only (control) or with supplemental LED

lights (Pro Series 325, LumiGrow, Inc., Emeryville, CA, USA), which provided light

with red/blue PPFD ratio of 4:1, and peak wavelengths of 665 nm and 440 nm. Four SL

treatments with average PPFD of 50, 80, 110, and 140 µmol·m-2·s-1 were achieved at

the container level from LED SL by varying the number of fixtures and the intensity

settings on each fixture. Spectral distribution and PPFD were measured using a

USB2000+ UV/VIS spectrometer (Ocean Optics, Inc., Dunedin, FL, USA). The lights,

controlled by Argus system (Argus Control Systems Ltd., British Columbia, Canada),

were turned on/off at 16/0.5 h before dusk, to achieve a 16-h photoperiod. The available

natural and supplemental DLI inside the experimental greenhouse are presented in

Table 1. The treatments were arranged following a randomized block design (5

treatments × 4 blocks). In each block, each treatment plot consisted of 50 cells linked

with each other, and each cell had three pea plants.

Growth, yield and quality measurements

At 5, 12, 19, and 26 d after the treatments were initiated, sixteen plants were

randomly sampled from each treatment during each investigation time to measure the

main stem length and count the number of fully expanded leaves on the main stem.

Stem extension rate (SER; cm·wk-1) and leaf expansion rate (LER; no.·wk-1) from 5 to

26 d after the start of treatment were calculated using Eqs. (1) and (2), respectively:

SER = (LS26 – LS5) / 3 (1)

LER = (LN26 – LN5) / 3 (2)

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where LS26 and LS5 are main stem length at 26 and 5 d after the start of treatment,

respectively, and LN26 and LN5 are the number of fully expanded leaves at 26 and 5 d

after start of treatment, respectively. The denominator, ‘3’ represents the number of

weeks used for calculation of SER and LER.

During each harvest, the pea shoots harvested from all the cells in each plot were

counted and weighed. The yield (kg·m-2 and shoots·m-2) from each harvest was

calculated, which was then added to previous yield(s) for determining the cumulative

yield. The total yield was determined by the cumulative yield of all the harvests.

Immediately after harvest, chlorophyll content index (greenness index) was

measured using a CCM-200 meter (Opti-sciences, Tyngsboro, MA, USA) on the fully

expanded leaflets of 16 randomly selected pea shoots from each treatment. Fresh mass

(FM) of pea shoots was recorded before being dried in an oven at 65 ºC for dry mass

(DM) measurement. Pea shoot succulence (g H2O·g-1 DM) was calculated as:

Succulence = (FM - DM) / DM (3)

Another 16 pea shoots from each treatment were randomly selected to determine

stem firmness utilizing a digital luggage scale (ML6194BK, ACI Brands, Inc., Oakville,

ON, Canada). The measurement method is a modification of test technique found in

Perez-Harguindeguy et al (2013). The hook of the scale was put on the middle of the

pea shoot with both ends fixed to leave around 5-cm middle portion for firmness

measurement, and the scale was pulled slowly, with increasing force, until breaking the

pea shoot, and the reading was recorded as tearing force (lb). Pea shoot firmness

(N·cm-2) was calculated as:

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Shoot firmness = 4.48 × tearing force / (0.402 × shoot diameter) (4)

where 4.48 is the unit converter from lb to N, and 0.402 is the scale hook diameter (cm).

The shoot diameter (cm) was measured at the middle position using a Vernier caliper.

The broken shoots were homogenized using a blender, and the filtered juice was used

for the measurement of soluble solid content (SSC, ºBrix) using a digital pocket

refractometer (PAL-1, Spectrum Technologies Inc., Aurora, IL, USA).

Statistical analysis

Data were subjected to analysis of variance using Data Processing System software

(DPS Version 7.05; Refine Information Tech. Co., Hangzhou, China) and were

presented as mean ± SE. Separation of means was performed using Duncan’s New

Multiple Range Test at the P ≤ 0.05 level. Regression analyses were used to determine

the relationships between SL and plant growth and yield.

RESULTS

Plant growth

Effects of SL on length of main stem and number of fully expanded leaves only

started to show 12 and 19 d from the start of treatment, respectively (Fig. 2A and C).

Weekly average SER increased linearly with increasing supplemental PPFD, but there

were no treatment effects on LER (Fig. 2B and D).

Crop yield

Throughout five harvests, cumulative yield (kg·m-2), increased linearly with

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increasing supplemental PPFD, with about 1.6- and 2-fold increases under SL of 110

and 140 µmol·m-2·s-1, respectively, compared to those under the control (no SL

treatment; Fig. 3A), but there were no treatment effects on the number of harvested

shoots (no.·m-2; Fig. 3B).

Pea shoot quality

The harvested pea shoots appeared to have thicker stems and larger leaflets under SL

than under no SL, which was supported by increased individual shoot fresh mass under

all SL treatments compared to the control (Table 2). However, only SL of 80–140

µmol·m-2·s-1 had higher SSC than no SL, while there were no differences in this trait

among SL of 50, 80, and 110 µmol·m-2·s-1 (Table 2). Supplemental lighting of 110–140

µmol·m-2·s-1 induced a lower succulence and higher firmness than the control (Table 2).

Although the green color of pea shoots appeared darker under SL than no SL, there was

no difference in chlorophyll content index among all treatments, which ranged from

28.8 ± 0.9 to 30.4 ± 0.9 (data not shown). Overall, SL of 50–80 µmol·m-2·s-1 resulted in

the best integrated quality.

Discussion

Supplemental LED lighting can promote pea shoot growth

Light is essential for normal growth of most plants. For peas, increasing light level

accelerates all phases of shoot growth and differentiation (Thomson and Miller 1963).

In the present study, SL of 50–140 µmol·m-2·s-1 PPFD increased main stem length and

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number of leaves immediately before the first harvest, relative to no SL. In addition to

increasing PPFD, SL extended the photoperiod, and increased total DLI from 5.3 to

8.1–13.1 mol·m-2·d-1, compared with no SL. Extending photoperiods are known to

promote shoot elongation in some greenhouse crops such as roses (Bredmose 1993). A

previous study of greenhouse plants by Faust (2002) indicated that for most species, an

increase in DLI from around 5 to 10 mol·m-2·d-1 resulted in taller plants which had more

leaves, presumably because the plants grown under low DLI lacked sufficient

photo-assimilate to produce a vigorous primary shoot.

It has been demonstrated that increasing light levels can promote plant growth rates

(Moe 1997). In the present study, stem extension rate increased linearly with increasing

supplemental PPFD. Normally, the first harvest of pea shoots occurs when plants are

15–20 cm tall by clipping off the growing point plus one pair of leaves (Miles and

Sonde 2003). This means that higher growth rates, especially stem extension rate,

resulting from SL may increase early yield of pea shoots.

It is worthwhile to note that there were similar rates of leaf unfolding between all

treatments for the first 12 d after the start of treatment (i.e., 18 d after sowing). A

previous study in peas indicated that morphogenetic effects of light on leaf growth was

largely limited to later growth stages (Thomson and Miller 1961), possibly because

carbohydrate reserves in cotyledons can provide sufficient nutrition for leaf production

in earlier stages (Low 1970).

Supplemental LED lighting can increase pea shoot yield.

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When natural light levels were low, yield of tomatoes increased with increasing

level of SL with LEDs (Lu et al. 2012). Similar LEDs SL effects on pea shoot yield

were obtained in the present study; SL of 50–140 µmol·m-2·s-1 increased harvested

shoot mass, in comparison with no SL, and yield increased incrementally with each

increase in amount of light. The physiological process leading to increased crop yields

associated with increasing levels of SL could involve an increased leaf photosynthetic

rate due to SL, and a corresponding increase in assimilate supply to harvested parts (Lu

et al., 2012). A previous study in peas showed that higher light intensities resulted in

greater carboxylation and higher rates of net carbon exchange (Bethlenfalvay and

Phillips 1977).

The higher yield (kg·m-2) of pea shoots associated with SL can be attributed to the

greater FM of individual shoots under higher light conditions, since numbers of

harvested shoots were similar among all treatments (Table 2, Fig. 3). In peas, increasing

light has been shown to result in a thickening of shoot internodes due to the production

of larger and greater quantity of cells (Thomson and Miller 1962).

Supplemental LED lighting can affect pea shoot quality.

Appearance, sweetness, tenderness and succulence are the major qualities valued in

the palatability of pea shoots, with larger, sweeter and less firm and more succulent pea

shoots normally favored by most consumers (Miles and Sonde 2003). In the present

study, SL had both positive and negative effects on these quality attributes.

Higher levels of SL improved appearance and pea shoot SSC. For appearance, SL of

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50–140 µmol·m-2·s-1, compared with no SL, resulted in thicker and more leafy pea

shoots, which was supported by a greater individual FM (Table 2). Furthermore, in the

present study, SL of 80–140 µmol·m-2·s-1 increased pea shoot SSC compared to the

control. The increased SSC could positively affect flavor (Mattheis and Fellman 1999).

Similar effects of SL on SSC have been reported in other crop species, such as tomato

(Demers and Gosselin 1999), mustard and kohlrabi (Samuolienė et al. 2013), and dill

and parsley (Bliznikas et al. 2012).

The higher intensities of SL increased firmness and reduced succulence of pea

shoots. First, in the present study, SL of 110–140 µmol·m-2·s-1 increased the firmness of

pea shoots compared with no SL. The increased firmness of pea shoots would tend to

reduce their tenderness, and thus palatability (Miles and Sonde 2003). Others have

shown that the increased firmness of pea shoots is derived mainly from higher fiber

content, and that higher light levels can promote fiber formation in plant tissues

(Thomson and Miller 1963; Moore and Jung 2001). Furthermore, SL of 110–140

µmol·m-2·s-1 reduced the succulence (i.e., water content) of pea shoots relative to no SL.

Similar light intensity effects have been reported on broccoli and tomato seedlings

(Dorais and Gosselin 2002), and turf (Hurdzan 1969).

Optimal light levels for pea shoot production

In the present study, within the range of 0 to 140 µmol·m-2·s-1, higher supplemental

PPFD resulted in better pea shoot growth and greater mass yield. However,

supplemental PPFD between 50–80 µmol·m-2·s-1 led to the best overall quality of pea

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shoots (Table 2). It appeared that even for the same crop species, the optimal light

requirement varies considerably between different physiological processes (Moe 1997).

To reach a balance on the consideration of yield and quality, the optimal PPFD of SL

possibly ranges between 50 and 80 µmol·m-2·s-1 for this trial. This is similar to the

supplemental PPFD of 50–100 µmol·m-2·s-1 that was recommended for leafy vegetable

production in greenhouses in Quebec from mid-November to mid-February, using HPS

lamps with a photoperiod of 12 to 16 h (Dorais 2003).

Besides intensity, photoperiod is another factor to be considered in order to fully

optimize light level for a given crop and production system (Hemming 2011). In

greenhouse production, natural light conditions must also be taken into consideration.

So, total DLI (natural + supplemental) may be the best index to predict an optimal

supplemental light level for the greenhouse production of pea shoots (Moe 1997), since

plant growth is often closely correlated to the total DLI (Faust 2002). Based on the

present study, a mean natural DLI of 5.3 mol·m-2·d-1, combined with 15.5 h of 50 to 80

µmol·m-2·s-1 SL from LED (i.e., 2.8 to 4.5 mol·m-2·d-1 of supplemental DLI), would

result in a total DLI of 8.1–9.8 mol·m-2·d-1. This optimal DLI value from our trial falls

in the light range provided by a previous study, which indicated that the optimal total

DLI varies from about 8 to 50 mol·m-2·d-1 for different crop species (Moe 1997).

However, study of SL using HPS lamps in Quebec suggested that around 13 mol·m-2·d-1

was a desirable light level for greenhouse lettuce production (Dorais 2003). The gap

between our result and the above recommended DLI might be due to differences in crop

species, lamp types, and greenhouse environmental conditions. Nevertheless, the

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suggested light level range from our results will provide potentially useful information

for pea shoots cultivation during the darkest months in northern climates. Based on the

target DLI range, a control system can make maximum use of the hours of the day with

off-peak electricity rates to operate SL system (Both 2000), and using dimmable LEDs

can even dynamically change light intensity, within the suggested range, according to

moment-to-moment variation of natural light levels (Pinho et al. 2013).

In summary, the results of the present study confirm our hypotheses. Supplemental

LED lighting can promote plant growth, increase yield, and improve some quality traits

of greenhouse-grown pea shoots during winter months in Southern Ontario. When daily

air temperature inside greenhouse is set at around 13 °C, a total DLI of 8.1–9.8

mol·m-2·d-1 can be suggested as a target light level for greenhouse pea shoot production.

References

Bethlenfalvay, G. J. and Phillips, D. A. 1977. Effect of light intensity on efficiency of carbon

dioxide and nitrogen reduction in Pisum sativum L. Plant Physiol. 60: 868−871.

Bliznikas, Z., Žukauskas, A., Samuoliene, G., Viršile, A., Brazaityte, A., Jankauskiene, J.,

Duchovskis, P. and Novičkovas, A. 2012. Effect of supplementary pre-harvest LED

lighting on the antioxidant and nutritional properties of green vegetables. Acta Hort.

939: 85−91.

Both, A. J. 2000. Some thoughts on supplemental lighting for greenhouse crop production.

Bioresource Engineering Department of Plant Biology and Pathology Rutgers, The

State University of New Jersey New Brunswick, NJ: 08901-08500.

Page 16 of 28



For Review Only

http://horteng.envsci.rutgers.edu/ppt/papers/supplightingpaper.pdf.

Bredmose, N. 1993. Effects of year-round supplementary lighting on shoot development,

flowering and quality of two glasshouse rose cultivars. Sci. Hort. 54: 69−85.

Choi, H. G., Moon, B. Y. and Kang, N. J. 2015. Effects of LED light on the production of

strawberry during cultivation in a plastic greenhouse and in a growth chamber. Sci.

Hort. 189: 22−31.

Chow, W. S. and Anderson, J. M. 1987. Photosynthetic responses of Pisum sativum to an

increase in irradiance during growth. I. Photosynthetic activities. Funct. Plant Biol. 14:

1−8.

Critten, D. L. 1993. A review of the light transmission into greenhouse crops. Acta Hort. 328:

9−32.

Demers, D. and Gosselin, A. 1999. Supplemental lighting of greenhouse vegetables: limitations

and problems related to long photoperiods. Acta Hort. 481: 469−473.

Demers, D. A. and Gosselin, A. 2002. Growing greenhouse tomato and sweet pepper under

supplemental lighting: optimal photoperiod, negative effects of long photoperiod and

their causes. Acta Hort. 580: 83−88.

Demers, D. A., Gosselin, A. and Wien, H. C. 1998. Effects of supplemental light duration on

greenhouse sweet pepper plants and fruit yields. J. Am. Soc. Hortic. Sci. 123: 202−207.

Dorais, M. 2003. The use of supplemental lighting for vegetable crop production: light intensity,

crop response, nutrition, crop management, cultural practices. Canadian Greenhouse

Conference, Oct. 9, 2003, Toronto, Ontario.

https://www.agrireseau.net/legumesdeserre/documents/cgc-dorais2003fin2.pdf.

Page 17 of 28



For Review Only

Dorais, M. and Gosselin, A. 2002. Physiological response of greenhouse vegetable crops to

supplemental lighting. Acta Hort. 580: 59−67.

Faust, J. E. 2002. First Research Report. Light Management in Greenhouses. I. Daily Light

Integral: A Useful Tool for the US Floriculture Industry.

http://www.specmeters.com/assets/1/7/A051.pdf.

Gaudreau, L., Charbonneau, J., Vézina, L.-P. and Gosselin, A. 1994. Photoperiod and

photosynthetic photon flux influence growth and quality of greenhouse-grown lettuce.

HortScience. 29: 1285−1289.

Giacomelli, G. A. and Roberts, W. J. 1993. Greenhouse covering systems. HortTechnology. 3:

50−58.

Hao, X., Guo, X., Chen, X. and Khosla, S. 2015. Inter-lighting in mini-cucumbers: interactions

with overhead lighting and plant density. Acta Hort. 1107: 291−296.

Hemming, S. 2011. Use of natural and artificial light in horticulture-interaction of plant and

technology. Acta Hort. 907: 25−35.

Hendricks, P. 2012. Life Cycle Assessment of Greenhouse Tomato (Solanum lycopersicum L.)

Production in Southwestern Ontario, University of Guelph. Master's dissertation,

Guelph, Canada.

Hurdzan, M. J. 1969. Effect of light intensity on seedling growth in red fescue (festuca rubra L.),

The University of Vermont. Master's dissertation, Burlington, USA.

Korczynski, P. C., Logan, J. and Faust, J. E. 2002. Mapping monthly distribution of daily light

integrals across the contiguous United States. HortTechnology. 12: 12−16.

Lim, T. K. 2012. Pisum sativum, p. 849−866. Edible Medicinal and Non-medicinal Plants.

Page 18 of 28



For Review Only

Springer, Netherlands.

Liu, W., Yang, Q., Qiu, Z. and Zhao, J. 2014. Effects of light intensity and nutrient addition on

growth, photosynthetic pigments and nutritional quality of pea seedlings. Acta Hort.

1037: 391−396.

Llewellyn, D., Zheng, Y. and Dixon, M. 2013. Survey of how hanging baskets influence the light

environment at lower crop level in ornamental greenhouses in Ontario, Canada.

HortTechnology. 23: 823−829.

Low, V. H. K. 1970. Effects of light and darkness on the growth of peas. Aust. J. Biol. Sci. 24:

187−196.

Lu, N., Maruo, T., Johkan, M., Hohjo, M., Tsukagoshi, S., Ito, Y., Ichimura, T. and Shinohara, Y.

2012. Effects of supplemental lighting with light-emitting diodes (LEDs) on tomato

yield and quality of single-truss tomato plants grown at high planting density. Environ.

Control Biol. 50: 63−74.

Mattheis, J. P. and Fellman, J. K. 1999. Preharvest factors influencing flavor of fresh fruit and

vegetables. Postharvest Biol. Technol. 15: 227−232.

McCree, K. J. 1971. The action spectrum, absorptance and quantum yield of photosynthesis in

crop plants. Agric. Meteorol. 9: 191−216.

Miles, C. A. and Sonde, M. 2003. Pea Shoots. Washington State University Cooperative

Extension.

https://www.researchgate.net/profile/Carol_Miles3/publication/242372648_Pea_Shoots

/links/54c7e47b0cf289f0cece3d18.pdf.

Mitchell, C. A., Dzakovich, M. P., Gomez, C., Lopez, R., Burr, J. F., Herna´ndez, R., Kubota, C.,

Page 19 of 28



For Review Only

Currey, C. J., Meng, Q. and Runkle, E. S. 2015. Light-emitting diodes in horticulture.

Hortic. Rev. 43: 1−87.

Moe, R. 1997. Physiological aspects of supplementary lighting in horticulture. Acta Hort. 418:

17−24.

Moore, K. J. and Jung, H. J. G. 2001. Lignin and fiber digestion. J. Range Manag. 54: 420−430.

Morrow, R. C. 2008. LED lighting in horticulture. HortScience. 43: 1947−1950.

Nelson, J. A. and Bugbee, B. 2014. Economic analysis of greenhouse lighting: light emitting

diodes vs. high intensity discharge fixtures. PLoS One. 9: e99010.

Olle, M. and Virsile, A. 2013. The effects of light-emitting diode lighting on greenhouse plant

growth and quality. Agr. Food Sci. 22: 223−234.

Papadopoulos, A. P., Demers, D. A. and Theriault, J. 2002. The Canadian greenhouse vegetable

industry with special emphasis on artificial lighting. Acta Hort. 580: 29−33.

Perez-Harguindeguy, N., Diaz, S., Garnier, E., Lavorel, S., Poorter, H., Jaureguiberry, P.,

Bret-Harte, M. S., Cornwell, W. K., Craine, J. M. and Gurvich, D. E. 2013. New

handbook for standardised measurement of plant functional traits worldwide. Aust. J.

Bot. 61: 167−234.

Pinho, P., Hytonen, T., Rantanen, M., Elomaa, P. and Halonen, L. 2013. Dynamic control of

supplemental lighting intensity in a greenhouse environment. Lighting Res. Technol. 45:

295−304.

Poel, B. R. and Runkle, E. S. 2017. Seedling growth is similar under supplemental greenhouse

lighting from high-pressure sodium lamps or light-emitting diodes. HortScience. 52:

388−394.

Page 20 of 28



For Review Only

Runkle, E. 2011. Lighting Greenhouse Vegetables, Greenhouse Product News, pp. 42.

Samuolienė, G., Brazaitytė, A., Jankauskienė, J., Viršilė, A., Sirtautas, R., Novičkovas, A.,

Sakalauskienė, S., Sakalauskaitė, J. and Duchovskis, P. 2013. LED irradiance level

affects growth and nutritional quality of Brassica microgreens. Cent. Eur. J. Biol. 8:

1241−1249.

Santos, J., Herrero, M., Mendiola, J. A., Oliva-Teles, M. T., Ibáñez, E., Delerue-Matos, C. and

Oliveira, M. 2014. Assessment of nutritional and metabolic profiles of pea shoots: The

new ready-to-eat baby-leaf vegetable. Food Res. Int. 58: 105−111.

Singh, D., Basu, C., Meinhardt-Wollweber, M. and Roth, B. 2015. LEDs for energy efficient

greenhouse lighting. Renew. Sustain. Energy Rev. 49: 139−147.

Thomson, B. F. and Miller, P. M. 1961. Growth patterns of pea seedlings in darkness and in red

and white light. Am. J. Bot. 48: 256−261.

Thomson, B. F. and Miller, P. M. 1962. The role of light in histogenesis and differentiation in the

shoot of Pisum sativum. I. The apical region. Am. J. Bot. 49: 303−310.

Thomson, B. F. and Miller, P. M. 1963. The role of light in histogenesis and differentiation in the

shoot of Pisum sativum. III. The internode. Am. J. Bot. 50: 219−227.

Wojciechowska, R., Długosz-Grochowska, O., Kołton, A. and Zupnik, M. 2015. Effects of LED

supplemental lighting on yield and some quality parameters of lamb's lettuce grown in

two winter cycles. Sci. Hort. 187: 80−86.

World Meteorological Organization. 2008. Guide to meteorological instruments and methods of

observation. Secretariat of the World Meteorological Organization, Geneva,

Switzerland. .

Page 21 of 28



For Review Only

Zhang, F. M. 2001. Protected Horticultural Science. Agriculture Publisher Ltd., Beijing, China.

Zhang, G. and Hu, Y. 2008. Production Technology of Sprouts and Microgreens. Jin Dun

Publishing House, Beijing, China.

Zheng, Y. 2016. Are LEDs the right choice for my operation?, Greenhouse Canada, pp. 14.

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Table 1. Supplemental light and total light level under each treatment.

Supplemental

PPFDa

(µmol·m-2·s-1)

Supplemental

DLIb

(mol·m-2·d-1)

Total (natural + supplemental) DLI (mol·m-2·d-1)

Before harvest During harvest Average

0 0 3.3 6.6 5.3

50 2.8 6.1 9.4 8.1

80 4.5 7.8 11.1 9.8

110 6.1 9.4 12.7 11.4

140 7.8 11.1 14.4 13.1

a PPFD: Photosynthetic photon flux density.

b DLI: Daily light integral.

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Table 2. Quality traits of pea shoots under different supplemental lighting PPFD.

SL PPFDa

(µmol·m-2·s-1)

Individual FMb

(g)

SSCc

(°Brix)

Succulence

(g H2O·g-1 DM)

Stem firmness

(N·cm-2)

0 0.68 ± 0.02 c 10.3 ± 0.1 c 8.20 ± 0.21 a 27.4 ± 3.0 b

50 0.89 ± 0.02 b 10.5 ± 0.3 bc 7.82 ± 0.17 ab 30.8 ± 2.6 ab

80 1.03 ± 0.06 b 11.0 ± 0.3 b 7.64 ± 0.34 ab 33.3 ± 2.9 ab

110 1.22 ± 0.09 a 11.0 ± 0.2 b 7.55 ± 0.13 b 34.8 ± 2.5 a

140 1.30 ± 0.08 a 11.7 ± 0.1 a 7.58 ± 0.26 b 37.4 ± 4.1 a

Note: Data are means ± SE (n = 16). The values in the same column followed by the

same letter are not significantly different at P ≤ 0.05 according to Duncan's New

Multiple Range Test.

a SL: Supplemental lighting. PPFD: Photosynthetic photon flux density.

b FM: Fresh mass.

c SSC: Soluble solid content.

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Fig. 1. Natural light conditions (A), air temperature and relative humidity (B) inside the

experimental greenhouse. Data are weekly means. DLI: daily light integral. Daylight

hours are calculated as the total length (hours) of time when solar radiation is above 120

W·m-2 within each day (World Meteorological Organization 2008).

Fig. 2. Relationship between pea shoot growth before the first harvest and supplemental

photosynthetic photon flux density (PPFD) of 0, 50, 80, 110, and 140 µmol·m-2·s-1. SL:

Supplemental lighting. The numbers: 5, 12, 19, and 26 in the legend of A and C

indicate days from the start of lighting treatments. SER (stem extension rate;

mm·wk-1) and LER (leaf expansion rate; no.·wk-1) were calculated for the period of

5–26 d after the start of treatments. Data are means ± SE (n = 4). Regression lines are

only shown where the effect of SL PPFD is significant at P ≤ 0.05.

Fig 3. Relationship between cumulative yield of pea shoots based on fresh mass (A) or

shoot number (B) during five harvests and supplemental PPFD: 0, 50, 80, 110, and

140 µmol·m-2·s-1. SL: Supplemental lighting. PPFD: Photosynthetic photon flux

density. The numbers 1–5 in the legend indicate the different harvests in

chronological order. Data are means ± SE (n = 4). Regression lines are only shown

where the effect of SL PPFD is significant at P ≤ 0.05.

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Fig. 1.

0

1

2

3

4

5

6

7

8

9

1 2 3 4 5 6 7 8 9 10

Time after start of treatment (wk)

DLI (m

ol m

-2 d

-1)

0

2

4

6

8

10

Daylight hours

(h)

DLIDaylight hours

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10

Time after start of treatment (wk)

Air tem

pera

ture

(℃

)

0

20

40

60

80

100

Rela

tive h

um

idity (%

)

Air temperature Relative humidity

A B

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Fig. 2.

30

60

90

120

150

180

210

Ste

m length

(m

m)

5 12 19 26

18

22

26

30

34

0 30 60 90 120 150

SE

R (m

m w

k-1)

0

1

2

3

4

5

0 30 60 90 120 150

SL PPFD (µmol m -2 s -1)

Leaf num

ber (n

o.)

5 12 19 26

0.0

0.4

0.8

1.2

1.6

0 30 60 90 120 150

SL PPFD (µmol m-2 s

-1)

LER

(no.

wk

-1)

A B

C D

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Fig. 3.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 30 60 90 120 150


Cum

ula

tive y

ield

(kg m

-2) 1 2 3 4 5

0

500

1000

1500

2000

2500

3000

0 30 60 90 120 150


Cum

ula

tive y

ield

(no. m

-2) 1 2 3 4 5

A B

Page 28 of 28



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