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Tolerance of Lisianthus to High Ammonium Levels inRockwool CultureRosalinda Mendoza-Villarreala, Luis A. Valdez-Aguilara, Alberto Sandoval-Rangela, ValentínRobledo-Torresa & Adalberto Benavides-Mendozaa

a Departamento de Horticultura, Universidad Autónoma Agraria Antonio Narro, Saltillo,Coah, MéxicoAccepted author version posted online: 27 May 2014.

To cite this article: Rosalinda Mendoza-Villarreal, Luis A. Valdez-Aguilar, Alberto Sandoval-Rangel, Valentín Robledo-Torres &Adalberto Benavides-Mendoza (2014): Tolerance of Lisianthus to High Ammonium Levels in Rockwool Culture, Journal of PlantNutrition, DOI: 10.1080/01904167.2014.920379

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Tolerance of Lisianthus to High Ammonium Levels in Rockwool Culture

Rosalinda Mendoza-Villarreal, Luis A. Valdez-Aguilar, Alberto Sandoval-Rangel, Valentín

Robledo-Torres, Adalberto Benavides-Mendoza

Departamento de Horticultura, Universidad Autónoma Agraria Antonio Narro, Saltillo, Coah.,

México

Address correspondence to Luis A. Valdez-Aguilar: Departamento de Horticultura, Universidad

Autónoma Agraria Antonio Narro, Saltillo, Coah., México. E-mail: luisalonso.valdez@uaaan.mx

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ABSTRACT

Nitrogen (N) by form of nutrition, ammonium (NH4+) or nitrate (NO3

–), affects metabolic and

physiological processes of plants. In general, a high proportion of N in the NH4+ form results in

poor growth of plants. Nonetheless, a number of species exhibit optimum growth when high

levels of NH4+ are provided. In the present study, lisianthus [Eustoma grandiflorum (Raf.) Shinn]

was grown in rockwool cultures and irrigated with nutrient solutions containing 15 mM N with

varying proportions of NH4+ and NO3

–. The results showed that an increase in NH4+-N form

increased plant height, number of flowers and leaves, leaf area, and shoot, stem, and leaf dry

weight. The proportion of NH4+ also affected leaf concentration of phosphorus, potassium (K),

calcium (Ca), and magnesium (Mg), although leaf N concentration was unaffected. Potassium

leaf concentration was higher when a low proportion of NH4+ was supplemented in the nutrient

solution; however, plants exhibited a decrease in leaf K concentration and a decrease in leaf Ca

as the proportion of NH4+-N increased. Shoot dry weight was higher with low leaf K whereas

high leaf Ca was associated with high shoot dry weight. Net photosynthesis rate was higher in

plants irrigated with solutions containing 75% of total N in NH4+ form than in those irrigated

with solutions of 0 or 25%. The results suggest that lisianthus can tolerate high levels of NH4+,

probably associated with a higher assimilation of Ca.

Keywords: Nitrate:ammonium ratio, Nitrogen nutrition, Nutrient solution, Soilless culture

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INTRODUCTION

The form by which nitrogen (N) is absorbed by plants, ammonium (NH4+) or nitrate (NO3

–),

markedly affects metabolic and physiological processes (Gerendás et al., 1997). This response is

due partially to the effect of the uptake of different N forms on cytosol and rhizosphere acidity,

which in turn affects availability of nutrients essential for plant growth and development. In

general, a high proportion of N supplemented as NH4+ results in poor growth of most of plants

species; however, contrasting results have been reported. Gaiad et al. (2006) indicated that, with

NH4+ nutrition, seedlings of mate plant (Ilex paraguariensis St. Hil.) exhibited increased leaf

area, leaf number, and net photosynthesis; nonetheless, in two cultivars of strawberry plants

(Fragaria × ananassa Duch), a supplement of NH4+ at 75% of total N resulted in decreased leaf

area, leaf fresh weight, and leaf dry weight (Tabatabaei et al., 2006).

The negative effects of high NH4+ proportions on plant growth have been associated with

acidification in the root zone (Walch-Liu et al., 2000; Claussen and Lenz, 1999), an action that

affected growth due to direct high acidity effects or reductions in cations uptake, such as

potassium (K) (Arnozis et al., 1988). Excessive NH4+ nutrition also has been associated with

plant hormones status since the biosynthesis of ethylene and polyamines are triggered under such

conditions; severe changes in the levels of aminoacids and organic acids such as citrate have

been also observed (Britto and Kronzucker, 2002; Zhang and Rengel, 1999; Gerendás et al.,

1997; Redinbaugh and Campbell, 1993; Barker and Corey, 1991).

Lisianthus [Eustoma grandiflorum (Raf.) Shinn] is a species that was introduced recently

in the market of ornamental plants (Harbaugh, 2007). Native to the arid and semiarid regions of

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south United States (Halevy and Kofranek, 1984) and north México (Harbaugh, 2007), its

cultivation has extended worldwide. Little research has been conducted though as to the

nutritional demands of lisianthus. It has been reported that increasing N concentration in the

nutrient solution from 0 to 400 mg L-1 resulted in improved growth in lisianthus (Freet et al.,

1988) whereas concentration from 250 to 300 mg L-1 results in higher chlorophyll concentration

and photosynthesis rate (Marchese et al., 2005). However, as there are not reports defining the

optimum proportion of N form, the present study was conducted to determine the effect of the

proportion of NH4+ and NO3

– in nutrient solutions on growth, internal macronutrient status, and

photosynthetic rate on lisianthus cultivated in rockwool.

MATERIALS AND METHODS

The study was conducted in a greenhouse located in Saltillo, Coah., México (25° 27 North

Latitude, 101° 02 West Longitude, 1610 meters above sea level) and equipped with automatic

control of temperature. Average daytime photosynthetically active radiation (PAR) registered

throughout the experiment was 190.5 µmol m–2 s–1; maximum PAR, observed from 13:00 to

15:00, was 498.5 µmol m–2 s–1. Average maximum and minimum temperatures recorded were de

28.9 °C and 19.9°C, respectively.

Seeds of lisianthus [Eustoma grandiflorum Raf. (Shinn)] Echo Blue were sown on

sphagnum peat in 200 cell-rigid plastic trays on Feb. 26, 2008. Non-bolting seedlings of 4-cm

height and four leaf pairs were transplanted on May 8, 2008, in rockwool slabs of 100 × 20 × 7.5

cm. A total of 14 seedlings were planted on each slab and allowed to establish for one week

previous to treatment imposition.

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The treatments consisted of six nutrient solutions with a total N concentration of 15 mM.

Nutrient solutions were prepared at 75%, 50%, 37.5%, 25%, 12.5%, and 0% NH4+-N by varying

the amounts of ammonium sulfate, calcium nitrate, ammonium nitrate, ammonium chloride, and

potassium nitrate. The remaining N to complete the 15 mM was supplemented with NO3–-N. The

nutrient solutions contained also 1.6 mM phosphorus (P), 6.2 mM K, 6 mM calcium (Ca), 2.8

mM magnesium (Mg), and 0.1-0.2 mM sulfate. Micronutrients were supplemented at the

following concentrations: 5 ppm iron, 0.05 ppm zinc, 0.02 ppm copper, 0.7 ppm manganese, and

0.5 ppm boron. The pH of the nutrient solutions was adjusted to 6.8 with phosphorus acid

(H3PO4) previous preparation and average electrical conductivity was 2.7 dS m–1. Irrigation with

the nutrient solutions started on May 14, 2008 applying 2.5 L per slab three times a week;

leaching nutrient solution was not retrieved.

Harvesting was performed from Aug. 18 to Sept. 3 when plants had three flowers fully

open. Plant height was measured at harvest time as well as the diameter at the base of the main

stem, the number of leaves and flowers per plant, leaf area (LI-3100 Area Meter; LI-COR

Biosciences, Lincoln, NE, USA), and dry weight of leaves, flowers, and stems. Shoot dry weight

was calculated adding the partial weights of stems, flowers, and leaves. Plant parts were bagged

and placed in an oven at 70ºC for three days previous to weighing. Previous to drying, leaves

were washed twice in distilled water; once dry, the leaves were ground to pass a 20-mesh screen.

Ground samples were analyzed for N concentration with the Kjeldahl procedure (Chapman and

Pratt, 1961) and phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg)

concentrations were determined on acid digests [sulfuric acid (H2SO4):perchloric acid (HClO4)

(2:1ml)] (Alcántar and Sandoval-Villa, 1999) with inductively coupled plasma spectrometry

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(ICP-AES VARIAN, model Liberty; Varian Medical Systems, Palo Alto, CA, USA). On Aug. 5,

2008, net photosynthetic rate was measured on fully expanded young leaves in plants of selected

treatments (75%, 25%, and 0% NH4+) with an infrared gas analyzer (Li-6200; LI-COR

Biosciences, Lincoln, NE, USA).

Treatments were distributed in a randomized complete block design with four

replications. Each replication consisted on one rockwool slab with 14 plants uniformly

distributed. Analysis of data was with analysis of variance, trend analysis (linear, quadratic, and

cubic effects), and mean comparison with Tukey’s procedure; SAS version 8.02 (SAS Institute,

Inc. 2001, Cary, NC, USA) was used to process the data. Regression models were calculated

when associations between growth parameters or nutrient concentrations were observed.

RESULTS

Increasing NH4+-N form enhanced plant growth since lisianthus resulted with larger plant height

and increased number of flowers and leaves, leaf area, and shoot, stems, and leaf dry weight

(Table 1). The effect of NH4+ was predominantly lineal in most of these growth parameters and

the plants irrigated with solutions containing 50% or 75% of total N as NH4+ exhibited

significant enhancing effects compared to the other levels.

The proportion of NH4+ in the nutrient solution significantly affected leaf concentration

of P, K, Ca, and Mg, although leaf N concentration was unaffected (Table 2). The effect on leaf

P, Ca, and Mg concentration fitted a quadratic and/or cubic trend, whereas for leaf K

concentration the trend was lineal. At low NH4+ proportions in the nutrient solution, 0% or

12.5%, leaves exhibited a low concentration of P, Ca, and Mg; however, increasing the

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proportion of NH4+ to moderate levels, 12.5% to 37.5%, resulted in a significant increase in the

concentration of these nutrients. Higher NH4+ proportions, 50% to 75%, were associated with a

decrease in the concentration of leaf P, Ca, and Mg concentrations. Potassium leaf concentration

was higher when a low proportion of NH4+ was supplemented in the nutrient solution; however,

as the proportion of NH4+ was increased, plants exhibited a significant decrease in leaf K

concentration.

Leaf K concentration was associated with leaf Ca concentration. An increasing leaf K

concentration was associated with a decrease in leaf Ca with a quadratic trend (Figure 1). Leaf

concentration of K or Ca, was associated contrastingly with growth of lisianthus since shoot dry

weight was high with low leaf K (Figure 2) whereas high leaf Ca was associated with high shoot

dry weight (Figure 3).

Net photosynthesis rate was affected by the proportion of NH4+ in the nutrient solution.

Plants irrigated with solutions containing 75% of total N as NH4+ exhibited higher

photosynthesis rate than plants that received NH4+ at proportions of 25% or lower (Figure 4).

DISCUSSION

It is accepted widely that NO3– or mixtures of NO3

– with low proportions of NH4+ are the best

form for N supplementation in plants due to the toxic effect of a N nutrition based on high

proportions of NH4+ (Chen et al., 2005; Dong et al., 2004; Shen et al., 2003). Nonetheless, the

results of the present study indicated that growth of lisianthus is enhanced under N nutrition

based on high proportions of NH4+ mixed with low proportions of NO3

–. The tolerance of

lisianthus to high NH4+ rates also was detected at physiological levels since net photosynthesis

was higher when plants were irrigated with solutions containing a high proportion of NH4+.

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Comparable results have been reported in other plant species; in mate plant (I. paraguariensis St.

Hil.) an increase in leaf area, leaf number and net photosynthesis was detected when N was

supplemented exclusively in NH4+ form (Gaiad et al., 2006). Similarly, candelabra tree

(Araucaria angustifolia Bertol.) exhibited improved growth when NH4+ was provided compared

to exclusively NO3– fed plants, which exhibited a lower chlorophyll and N concentration in

young leaves than plant receiving NH4+ nutrition (Garbin and Dillenburg, 2008). In common

heather plants [Calluna vulgaris (L.) Hull] optimum growth was observed when NH4+ was the

sole N form supplemented (De Graaf et al., 1998).

In the present study, N form had no effect on leaf N concentration. This result suggests

that N assimilation in lisianthus was a function of total external N concentration since it was

maintained constant in all the nutrient solutions, and it was not dependent on the form on which

N was supplemented. However, N form did affect the assimilation of other plant nutrients.

Leaves of lisianthus resulted with increased P, Ca, and Mg when the proportion of NH4+ was

from 12.5% to 50% of total N.

Plants fed with NH4+ are reported to exhibit a K deficiency attributed to competition for

uptake sites (Hoopen et al., 2010; Hess et al., 2006) due to the similarities in both cations (Xu et

al., 2002; Wang et al., 1996). In the present study, lisianthus showed a lineal decrease in leaf K

concentration as NH4+ in the nutrient solution was increased, especially when its proportion was

from 50% to 75% of total N. The decrease in K leaf concentration was from 23% to 36% at these

NH4+ proportions, compared to plants that received only NO3

– N. Nonetheless, in spite of the

decrease in leaf K concentration, plants did not exhibit K deficiency symptoms and were able to

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reach optimum growth, suggesting that interactions with other nutrients may have resulted

positive for growth.

An excessive proportion of NH4+ has been reported to cause a decrease in Ca

concentration in plant tissues due to the antagonism between both cations (Siddiqi et al., 2002).

Nonetheless, lisianthus did not exhibit a decrease in leaf Ca concentration at high proportions of

NH4+ in the nutrient solution, but an increase in leaf Ca accumulation was detected at moderate

NH4+ proportions. This response may be related to the interaction of Ca with other nutrients,

specifically K, since an increase in leaf Ca was associated with a decrease in leaf K

concentration. Bar-Tal and Pressman (1996) reported similar results in tomato since there was a

decrease in tissue Ca concentration as external K was increased. The negative interaction

between K and Ca was confirmed by the association between a low leaf K and a high leaf Ca

concentration with a high shoot biomass accumulation by lisianthus plants and, in general, with

improved plant growth. Likewise, the higher net photosynthetic rate observed in plants irrigated

with solutions of high NH4+ proportions suggests that lisianthus was in adequate physiological

status so that plants were able to produce higher biomass.

The results observed in the present study suggest that lisianthus can tolerate high levels of

NH4+, probably due to an increase in calcium concentration. Further research is recommended to

assess the possibility of achieving higher tolerance of lisianthus to even higher NH4+ proportions

by increasing Ca concentrations in the nutrient solution or foliar spays.

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Table 1. Effect of varying proportions of NH4+ in the nutrient solution on growth parameters of

lisianthus grown in rockwool with N concentration maintained at 15 mM

% in nutrient solution

Dry weight g

NH4+ NO3

–

Number of

flowers

Plant height

cm

Leaf area cm2

Stem diameter

mm

Number of

leaves Leaf Flower Stem Shoot

0 100 12b 73.9ab 459d 3.98 47d 1.60d 1.92 2.60c 6.14c 12.5 87.5 15b 77.1a 690c 4.40 67c 2.20cd 2.34 3.55bc 8.11bc 25 75 14b 75.5a 825abc 4.56 72c 2.60bc 2.26 3.83ab 8.71b 37.5 62.5 14b 69.8b 718bc 4.31 81bc 2.47bc 2.02 3.19bc 7.69bc 50 50 16b 79.0a 874ab 4.61 95b 3.09ab 2.69 4.07ab 9.86ab 75 25 22a 74.1ab 970a 4.88 118a 3.67a 3.06 4.71a 11.45a

Anova *** * *** NS *** *** NS * ** Lineal *** NS *** * *** *** * ** ***

Quadratic NS NS NS NS NS NS NS NS NS Cubic * NS * NS NS NS NS NS NS

Means followed by the same letter indicate non-significant difference according to Tukey´s test

with P=0.05.

NS, *, **, *** non-significant and significant at P<0.05, 0.01, and 0.001, respectively, according

to F test

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Table 2. Effect of varying proportions of NH4+ in the nutrient solution on nitrogen (N),

phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentration in leaves of

lisianthus grown in rockwool with N concentration maintained at 15 mM

% in nutrient solution N P K Ca Mg NH4

+ NO3– mmol kg-1

0 100 2429 97cd 928a 120b 361b 12.5 87.5 2386 159ab 835ab 204a 395ab 25 75 2571 184a 832ab 166ab 426ab 37.5 62.5 2429 79d 860ab 141b 447a 50 50 2293 120bc 594c 182ab 379ab 75 25 2279 137b 702bc 173ab 371ab

Anova NS *** ** ** * Lineal NS NS *** NS NS

Quadratic NS * NS NS ** Cubic NS *** NS * NS

Means followed by the same letter indicate non-significant difference according to Tukey´s test

with P=0.05.

NS, *, **, *** non-significant and significant at P<0.05, 0.01, and 0.001, respectively, according

to F test

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FIGURE 1. Association between internal concentration of K and Ca in leaves of lisianthus

grown in rockwool in response to varying proportions of NH₄⁺ and

NO₃^- in the nutrient solutions. Bars represent the standard error of the

mean.

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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT 17

FIGURE 2. Association between leaf concentration of K and shoot dry mass accumulation at

experiment termination in plants of lisianthus grown in rockwool in response to varying

proportions of NH₄⁺ and NO₃^- in the

nutrient solutions. Bars represent the standard error of the mean.

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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT 18

FIGURE 3. Association between leaf concentration of Ca and shoot dry mass accumulation at

experiment termination in plants of lisianthus grown in rockwool in response to varying

proportions of NH₄⁺ and NO₃^- in the

nutrient solutions. Bars represent the standard error of the mean.

Dow

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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT 19

FIGURE 4. Effect of the proportion of NH₄⁺ and

NO₃^- in the nutrient solution on net photosynthesis rate in young

leaves of lisianthus grown in rockwool. Bars represent the standard error of the mean.

Dow

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