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Journal of Plant Nutrition

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Tiller Production and Development in Perennial Ryegrass in Relation to Nitrogen Use

R. Gisluma; S. M. Griffithb a Department of Plant Biology, The Danish Institute of Agricultural Sciences, Research Centre Flakkebjerg, Slagelse, DK, Denmark b United States Department of Agriculture, Agricultural Research Service, National Forage Seed Production Research Center, Corvallis, Oregon, USA Online publication date: 25 October 2004

To cite this Article Gislum, R. and Griffith, S. M.(2005) 'Tiller Production and Development in Perennial Ryegrass in

Relation to Nitrogen Use', Journal of Plant Nutrition, 27: 12, 2135 — 2148 To link to this Article: DOI: 10.1081/PLN-200034675 URL: http://dx.doi.org/10.1081/PLN-200034675

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JOURNAL OF PLANT NUTRITION Vol. 27, No. 12, pp. 2135–2148, 2004

Tiller Production and Development in Perennial Ryegrass in Relation to Nitrogen Use R. Gislum1,* and S. M. Griffith2 1

Department of Plant Biology, The Danish Institute of Agricultural Sciences, Research Centre Flakkebjerg, Slagelse, DK, Denmark 2 United States Department of Agriculture, Agricultural Research Service, National Forage Seed Production Research Center, Corvallis, Oregon, USA

ABSTRACT The amount of soil nitrogen (N) available to perennial ryegrass (Lolium perenne L.) will influence the distribution of N within the plant. At low amounts of plant available N the relative proportion of N in the roots will be high. As under conditions of high N availability, the proportion of N in vegetative and reproductive tillers as well as the number of vegetative and reproductive tillers will increase. However, the correlation between plant N content and tiller production is not known. Therefore, a growth chamber experiment was performed to investigate this relationship in perennial ryegrass.

*Correspondence: R. Gislum, Department of Plant Biology, The Danish Institute of Agricultural Sciences, Research Centre Flakkebjerg, Slagelse, DK-4200, Denmark; E-mail: [email protected]. 2135 DOI: 10.1081/LPLA-200034675 Copyright & 2004 by Marcel Dekker, Inc.

0190-4167 (Print); 1532-4087 (Online) www.dekker.com

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Gislum and Griffith The relation is important to better predict the effect of N application on tiller production. Plants were grown in nutrient solutions containing diminishing amounts of N over 36 days. At the end of the growth period, N and carbon (C) concentrations of the plant tissues, as well as the tiller production, were analyzed. Higher N concentrations were found in leaves than in roots. Depending on the N concentration in leaves, two groups of plants could be identified. One group (I) had an average leaf N concentration of 1–2%, which was distinct from the other group (II) with an average leaf N concentration of above 2%. At the end of the experimental period, the accumulated N content was equally distributed between roots, stems, and leaves in group I, whereas N was preferably stored in the leaves and stems in group II. The lowest production of tillers was achieved with 0.01 g N plant1, and the greatest number of tillers was reached with 0.19 g N plant1. The greatest number of tillers produced per plant in group II was reached before the end of the experimental period, indicating that maximum tiller production was reached under the given conditions. In group I, a linear model described the correlation between the number of tillers produced per plant and N content per plant. In group II, a model with an exponential rise to maximum described the relationship between these parameters. The results indicate, that the production of tillers in perennial ryegrass is closely related with N content in the plant. The results are further discussed in relation to N dynamics during vegetative and reproductive growth in perennial ryegrass. Key Words: Nitrogen distribution; Nitrogen concentration; C:N ratio; Tiller production.

INTRODUCTION The amount of N available for the plant will influence the distribution of N within the plant. Low amounts of plant-available N will change the distribution of N towards roots, which have shown to function as sink organs for mobilized N in perennial ryegrass (Lolium perenne L.) and colonial bentgrass (Agrostis capillaris L.) and to a lesser degree in red fescue (Festuca rubra L.).[1,2] Under these conditions, sufficient amounts of N will stimulate growth and development of the reproductive and vegetative tillers. Santos et al.[3] showed that N transport to new vegetative tillers in rough stalked meadow grass (Poa trivialis L.) stopped when the external N supply was reduced. Schulte auf’m Erley et al.[2] found similar results in perennial ryegrass,

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but red fescue still allocated high proportion of N reserves to tiller production. With regard to seed production, Warringa and Kreuzer[4] showed that vegetative tillers, which are initiated after anthesis in perennial ryegrass, have no influence on seed yield. Initially, new vegetative tillers as well as a number of reproductive tillers are dependent on carbohydrate and organic N supply from the main tiller, which can lead to competition for carbohydrates and N compounds between the main tiller and side tillers. In any case, the generation of reproductive tillers and the production of vegetative tillers indicate that sufficient amounts of N are available to the plants. In perennial ryegrass, primary induction of tillers depends upon either low temperature, short days, or both factors[5,6] with low temperature being the most important factor.[5] Secondary induction of tillers depends on long days.[5,7] Tillers developed during spring growing season are, therefore, not expected to be primary induced and thereby initiate reproductive growth. It has, however, been suggested that a flowering stimulus produced in the induced main tiller (direct induction) can be translocated to noninduced tillers on the same plant (indirect induction).[8] However, tillers emerging after primary induction initiating reproductive growth and thereby contributing to seed yield do not produce as large ears with as many spikelets and florets as early emerged tillers.[5] Early emergence of the tillers is therefore important to obtain a high seed yield. Consequently, to increase seed yield, it is important that reproductive tillers emerge as soon as possible after the initiation of spring growth and sufficient amounts of available N will accelerate this emergence. However, whether the relation between tiller production and plant N content is linear or nonlinear is not known. Therefore, aims of this experiment are to investigate the effect of different N treatments on the temporal distribution of N between different plant organs, to assess the potential total tiller production in plants growing with different N treatments, and to develop models that describe the relationship between total tiller production and N content per plant in perennial ryegrass.

MATERIALS AND METHODS Plant Material Seeds of perennial ryegrass (Lolium perenne L. cv. Linn) were sown in 278 mL black plastic pots and, after germination, the pots were thinned to one seedling per pot. The pots were filled with a commercial soil mix

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(Sunshine 400 series, McConkey Co., Sumner, WA, USA). When the third leaf was developed, the plants were vernalized in growth chambers (Model CMP3244, Conviron, Pembina, ND, USA) for 9 weeks at day/ night temperature of 7 C and irradiance at 250–300 mmol m2 s1. After vernalization, the plants were placed one week in an unheated glasshouse (Corvallis, OR, USA) for acclimation. After acclimation 100 plants were randomly divided into five groups and each group was placed in a container (length width ¼ 0.3 0.6 m). The plants were afterwards moved to growth chambers with a 16/8 h light/dark regime at 18/12 C (defined as the start of the experimental period, day 0). Tungsten bulbs gave a photon flux density of 250–300 mmol m2 s1 in the spectral range 400–700 nm. The five containers with 20 plants each were placed randomly in the climate chamber. At the start of the experiment, each container received a nutrient solution of the following composition (macronutrients): 1 mol m3 CaCl2, 1 mol m3 MgSO4, 1 mol m3 K2SO4, 0.1 mol m3 KH2PO4 and (micronutrients) 50 mmol m3 KCl, 2 mmol m3 MnSO4, 2 mmol m3 ZnSO4, 0.5 mmol m3 CuSO4, 25 mmol m3 H3BO3, 0.5 mmol m3 Na2MoO4, 40 mmol m3 FeEDTA. With the change of the nutrient solution every third day, the N concentration in each container was added at decreasing rates to lower N availability during plant development. Thus, the concentration of N (added as ammonium nitrate, 1:1) at each change of nutrient solution was calculated from Eq. (1): Nt ¼

N0 1 þ eðtt0 Þ=b

ð1Þ

where Nt and N0 denotes N concentration at day t and day zero, respectively. t0 and b were constants that were preset at 10.2 and 2.8, respectively. Five different N treatments were used with the following start concentration: 0.1 mM N (N0.1), 0.6 mM N (N0.6), 1.1 mM N (N1.1), 3.1 mM N (N3.1), and 6.1 mM N (N6.1) (Fig. 1).

Harvest Analysis Four randomly chosen plants (n ¼ 4) of each N rate (a total of 20 plants) were harvested at 9, 15, 24, 30, and 36 days after start of the experiment. At harvest occasions, the total number of tillers were registered, and plants were divided into roots, stems, senescent leaves (here defined as leaves where >50% of the leaf area was nongreen) and leaves. Fresh weight of the four plant organs was recorded before the material was dried at 80 C to determine dry weight. Plant material was

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N0.1 N0.6 N1.1 N3.1 N6.1

8 6 4 2 0

0 3 6 9 12 15 18 21 24 27 30 33 Days Figure 1. Nitrogen concentration in nutrient solution at each change every third day in the five treatments (N0.1, N0.6, N1.1, N3.1, and N6.1).

ground using a sample mill (Foss Tecator Cyclotec 1093, Ho¨gana¨s, Sweden) and analyzed for total C and N using a CHNS/O analyzer (Perkin Elmer 2400 Series II, Norwalk, CT, USA).

Statistics The statistical design used was a one-way factorial experiment with four replicates and with harvest occasions as the main factor. The statistical treatment of plant N concentration, C:N ratio and tiller number involved testing of harvest day within each N rate by F-tests. Data on plant N concentration, C:N ratio and tiller number were analyzed using a linear mixed model: Xhr ¼ þ h þ Ehr where Xhr is plant N concentration, C:N ratio or tiller number of the rth replicate at the hth harvest day, is a general mean, h is the hth harvest day main effect and Ehr are experimental error. All measured variables were assumed to be independently and normally distributed. To test the hypothesis of no harvest day effects on plant N concentration, C:N ratio or tiller number, the denominator used in the F-test was the mean square for the effect of harvest day and the denominator was the residual mean square. Means of harvest day were separated by pairwise comparison and were declared different at the 5% level of significance, if main effect was significant. The analyses of plant

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N concentration, C:N ratio and tiller number were performed using the PROC MIXED module within the Statistical Analysis System (version 8) software package.[9] Calculation of correlation coefficient between DM content in plants and harvest days were performed using a linear model ( f ¼ y0 þ a x). Calculation of correlation coefficient between the number of tillers per plant and N content per plant were performed by a linear model for N0.1, N0.6, and N1.1 and a model with an exponential rise to maximum ( f ¼ a(1 ebx)) for N3.1 and N6.1. Calculations of correlation coefficients were performed using SigmaPlot (version 7), software package.[10]

RESULTS Dry Matter Production and Plant Nitrogen Concentration Dry matter production (DM) increased with all N treatments during the experiment, and the relationship could be described using linear models (Fig. 2). The greatest plant N concentration (4.27%) was in leaves, and the lowest plant N concentration (0.56%) was in the roots (Fig. 3). For all organs, the greatest plant N concentration was with the N6.1 treatment. The N concentration in the leaves was greatest at the start of the experiment after which it decreased to approximately 1% at

DM content (g plant−1)


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14 12 10 8 6 4 2

N0.1 N0.6 N1.1 N3.1 N6.1

9

15

24

30

36

Days Figure 2. Dry matter (DM) content in perennial ryegrass as a function of growth period (days) at five nitrogen treatments (N0.1, N0.6, N1.1, N3.1, and N6.1). Vertical bars represent SE (n ¼ 4). Correlation coefficients are: N0.1 (r2 ¼ 0.98), N0.6 (r2 ¼ 0.99), N1.1 (r2 ¼ 0.97), N3.1 (r2 ¼ 0.97), and N6.1 (r2 ¼ 0.97).

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harvest day 36 for the N0.1 treatment. In the stems, N concentration for the N0.1, N0.6, and N1.1 treatments did not change during the experiment, whereas N concentration for the N6.1 treatment significantly decreased from harvest day 9 and 15 until harvest days 30 and 36. At the end of the experiment, N concentration in the stems for the N6.1 treatment was 2 times that at the N0.1 treatment. The N concentration in the roots decreased significantly in all N treatments from harvest day 9 until 30. From harvest day 30–36, this decrease was not significant. Two groups could be identified when N concentration was measured in leaves;

A

4 3 2 Nitrogen concentration (% in dry matter)



1 B

4 3 2 1 C

N0.1 N0.6 N1.1 N3.1 N6.1

4 3 2 1 9

15

24

30

36

Days

Figure 3. Nitrogen concentration in leaves (A), stems (B), and roots (C) of perennial ryegrass for five nitrogen treatments (N0.1, N0.6, N1.1, N3.1, and N6.1) and at five harvest occasions (9, 15, 24, 30, and 36 days after start of the experiment). Vertical bars represent SE (n ¼ 4).

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one with an average leaf N concentration of 1–2%, consisting of plants from the N0.1, N0.6, and N1.1 treatments and one with an average leaf N concentration above 2% consisting of plants from the N3.1 and N6.1 treatments (Fig. 3).

Distribution of Nitrogen and C:N Ratio in Different Organs If the average leaf N concentration was 1–2%, the preferable storage organ for N at the start of the experiment was leaves and roots, whereas at the end of the experiment N was equally shared between the different organs (Table 1). Senescent leaves accumulated only a minor amount of N (