Whole-plant Relative Growth Rate Research Articles

Shoot and Root Traits Underlying Genotypic Variation in Early Vigor and Nutrient Accumulation in Spring Wheat Grown in High-Latitude Light Conditions

Plants with improved nutrient use efficiency are needed to maintain and enhance future crop plant production. The aim of this study was to explore candidate traits for pre-breeding to improve nutrient accumulation and early vigor of spring wheat grown at high latitudes. We quantified shoot and root traits together with nutrient accumulation in nine contrasting spring wheat genotypes grown in rhizoboxes for 20 days in a greenhouse. Whole-plant relative growth rate was here correlated with leaf area productivity and plant nitrogen productivity, but not leaf area ratio. Furthermore, the total leaf area was correlated with the accumulation of six macronutrients, and could be suggested as a candidate trait for the pre-breeding towards improved nutrient accumulation and early vigor in wheat to be grown in high-latitude environments. Depending on the nutrient of interest, different root system traits were identified as relevant for their accumulation. Accumulation of nitrogen, potassium, sulfur and calcium was correlated with lateral root length, whilst accumulation of phosphorus and magnesium was correlated with main root length. Therefore, special attention needs to be paid to specific root system traits in the breeding of wheat towards improved nutrient accumulation to counteract the suboptimal uptake of some nutrient elements.

Optimal Leaf-to-Root Ratio and Leaf Nitrogen Content Determined by Light and Nitrogen Availabilities

Plants exhibit higher leaf-to-root ratios (L/R) and lower leaf nitrogen content (N area) in low-light than in high-light environments, but an ecological significance of this trait has not been explained from a whole-plant perspective. This study aimed to theoretically and experimentally demonstrate whether these observed L/R and N area are explained as optimal biomass allocation that maximize whole-plant relative growth rate (RGR). We developed a model which predicts optimal L/R and N area in response to nitrogen and light availability. In the model, net assimilation rate (NAR) was determined by light-photosynthesis curve, light availability measured during experiments, and leaf temperature affecting the photosynthesis and leaf dark respiration rate in high and low-light environments. Two pioneer trees, Morus bombycis and Acer buergerianum, were grown in various light and nitrogen availabilities in an experimental garden and used for parameterizing and testing the model predictions. They were grouped into four treatment groups (relative photosynthetic photon flux density, RPPFD 100% or 10%×nitrogen-rich or nitrogen-poor conditions) and grown in an experimental garden for 60 to 100 days. The model predicted that optimal L/R is higher and N area is lower in low-light than high-light environments when compared in the same soil nitrogen availability. Observed L/R and N area of the two pioneer trees were close to the predicted optimums. From the model predictions and pot experiments, we conclude that the pioneer trees, M. bombycis and A. buergerianum, regulated L/R and N area to maximize RGR in response to nitrogen and light availability.

Ethylene emission and responsiveness to applied ethylene vary among Poa species that inherently differ in leaf elongation rates.

A plant's ability to produce and respond to ethylene is essential for its vegetative growth. We studied whole-shoot ethylene emission and leaf growth responses to applied ethylene in four Poa spp. that differ inherently in leaf elongation rate and whole-plant relative growth rate. Compared with the fast-growing Poa annua and Poa trivialis, the shoots of the slow-growing species Poa alpina and Poa compressa emitted daily 30% to 50% less ethylene, and their leaf elongation rate was more strongly inhibited when ethylene concentration was increased up to 1 microL L(-1). To our surprise, however, low ethylene concentrations (0.02-0.03 microL L(-1)) promoted leaf growth in the two slow-growing species; at the same concentrations, leaf elongation rate of the two fast-growing species was only slightly inhibited. All responses were observed within 20 min after ethylene applications. Although ethylene generally inhibits growth, our results show that in some species, it may actually stimulate growth. Moreover, in the two slow-growing Poa spp., both growth stimulation and inhibition occurred in a narrow ethylene concentration range, and this effect was associated with a much lower ethylene emission. These findings suggest that the regulation of ethylene production rates and perception of the gas may be more crucial during leaf expansion of these species under non-stressful conditions and that endogenous ethylene concentrations are not large enough to saturate leaf growth responses. In the two fast-growing species, a comparatively higher ethylene endogenous concentration may conversely be present and sufficiently high to saturate leaf elongation responses, invariably leading to growth inhibition.

Gas exchange, water relations and osmotic adjustment in Phillyrea latifolia grown at various salinity concentrations.

Leaf gas exchange, water relations and osmotic adjustment were studied in hydroponically grown Phillyrea latifolia L. plants exposed to 5 weeks of salinity stress (0, 80, 160, 240 and 320 mM NaCl) followed by 5 weeks of treatment with half-strength Hoagland solution. Whole-plant relative growth rate and root/shoot and lateral/structural root ratios were also evaluated. Net CO2 assimilation rate, stomatal conductance and transpiration rate were markedly decreased by all of the salt treatments. Growth was also strongly depressed by all salt treatments, especially lateral root growth. Leaf water potential decreased soon after salinity stress was imposed, whereas there was a lag of several weeks before leaf osmotic potential decreased in response to the salt treatments. After 5 weeks of salinization, leaf turgor of salt-treated plants was similar to that of controls. Although Na+ + Cl- contributed little to the salt-induced changes in osmotic potential at full turgor (Psi(piFT)), the contributions of K+, mannitol (Man) and glucose (Glc) to Psi(piFT) markedly increased as external salinity increased. Salt accumulation was negligible in the youngest leaves, which mostly accumulated soluble carbohydrates and K+; in contrast, old leaves served as storage sinks for Na+ and Cl-. Photosynthetic performance of salt-treated plants fully recovered once salt was leached from the root zone, with the recovery rate depending on the severity of the salt stress previously experienced by the plants. Recovery of gas exchange occurred even though the leaves still had a salt load similar to that detected in leaves at the end of the 5-week salinity period, and had markedly lower concentrations of K+ and soluble carbohydrates than control leaves. We conclude that salt-induced water stress primarily controlled gas exchange of salt-treated P. latifolia leaves, whereas the salt load in the leaves did not cause irreversible damage to the photosynthetic apparatus.

Correlating source leaf photosynthesis and export characteristics of C3, C3-C4 intermediate and C4 Panicum and Flaveria species with whole-plant relative growth rate

Source leaves of 10 Panicum and 7 Flaveria C3, C3-C4 intermediate, and C4 species were fed 14CO2 in the mid-afternoon. Immediate export, calculated when isotopic equilibrium existed between 14CO2 and 14C-translocates, was compared with subsequent 14C-export during afternoon-nighttime chase periods. Immediate and daily export patterns were compared to the relative growth rates (RGR) of the plants calculated from whole-plant daily net carbon exchange. The C4 types fixed and exported the most during the feed within each genus. By comparison, immediate export rates during photosynthesis in Panicum type I C3-C4 intermediates were greater than those in C3 species. In contrast, immediate export was much lower in Flaveria type II C3-C4 intermediates than in their C3 and C4 relatives. In all species 14C-reserves, primarily starch and sugars, sustained export during the chase periods, but the extent to which subsequent day-night export compensated for lower export during the feed was greater among Panicum than Flaveria species. The Panicum type I C3-C4 intermediates still behaved in an intermediate manner with respect to daily 14C-export. In contrast, the Flaveria type II C3-C4 intermediates still had the lowest total 14C-export by the next morning. Overall, in both genera daily export correlated better with immediate export rates than with photosynthesis itself and other leaf export parameters. Among the Panicum, the correlation between whole-plant RGR and leaf function measured was not strong. However, among the Flaveria the correlation between whole-plant RGR was strongest with immediate export of the source leaf.

324 Heat Tolerance Varies with Species, Provenance, and Accession in Fragaria

Several components of whole-plant growth were compared among accessions of Fragaria chiloensis (FC) and F. virginiana (FV) grown at 23 and 31 °C daytime temperatures. The accessions loosely represented North American (NA) and South American (SA) provenances of FC and Kentucky (KY) and eastern Canadian (CN) provenances of FV. Differences in component values between species and by provenance and accession within species were observed at each temperature. Using the ratio of the component value at 31 °C to that at 23 °C as a basis for comparisons, whole-plant relative growth rate (RGR), leaf net assimilation rate (NAR), root RGR, and root: shoot ratio were reduced relatively more by high temperature in FC than FV, while crown RGR, leaf RGR, and leaves produced per day were not consistently affected by temperature or and did not differed significantly between species. While the SA FC exhibited higher values for nearly all components than the NA FC at both temperatures, both were affected similarly by high temperature. The CN FV exhibited somewhat greater sensitivity to high temperature than the KY FV, with significantly lower leaf NAR, crown RGR, and leaves produced per day in the former group.

Growth and Metabolism of Tomato Seedlings Grown with Roots Warm during the Day and Cold at Night, or Vice Versa

Do root temperatures warm during the day and cool during the night benefit plant growth? Tomato (Lycopersicon esculentum Mill.) seedlings were grown at a constant 20C air temperature but with varied root temperature, either 28/12C or 12/28C day/night for 8 days. Eight seedlings were grown in troughs in continuously flowing nutrient solution containing 200 μM \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(^{14}\mathrm{NO}_{3}^{-}\) \end{document} excess amounts of other mineral elements. The flow rate was 0.6 liters/day per trough on the first day, when plants weighed 20 mg, and increased with plant size. After 8 days, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(^{15}\mathrm{NO}_{3}^{-}\) \end{document} was provided for 12 h when roots were warm, and eight plants were harvested at the end of labeling or 12 h later. During the treatments, weight per plant increased more in leaves, 3.5 to 44 mg, than roots, 4.3 to 19 mg, and least for stem, 12 to 30 mg. The whole-plant relative growth rate did not differ among treatments, 0.17 to 0.19/day, but was less than for plants grown at a constant 20C root temperature, 0.22/day. Uptake of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(^{14}\mathrm{NO}_{3}^{-}\) \end{document} from the media and exudation from the stem of decapitated plants were greater when roots were warm than when roots were cold, regardless of light. After labeling for 12 h at the warm root temperature, 15N enrichment in plant tissues was greater with roots warm during the day, 0.20, 0.15, and 0.16, than in those with roots warm during the night, 0.16, 0.11, and 0.10, for roots, stems, and leaves, respectively. Enrichment with roots warm during the day was 22%, 33%, and 62% greater, for roots, stems, and leaves, respectively, than with roots warm during the night. However, uptake of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} at night by roots that were warm during the night was sufficient so that plants grown at out-of-phase root temperature grew as fast as plants grown at in-phase root temperature. Research supported in part by grant 93-37100-9101 from the NRI Competitive Grants Program/USDA.

Tradeoff between height and relative growth rate in a dominant grass from the Serengeti ecosystem.

We determined the relationship between plant height and whole-plant relative growth rate (g g-1 day-1) for ten genotypes of Sporobolus kentrophyllus collected from an intensively grazed site on the Serengeti Plains, Tanzania. Plants were grown for 7 weeks in a greenhouse in Syracuse, N.Y., and harvested weekly. Plants that received simulated bovine urine showed a negative relationship between plant height and growth rate, suggesting a genetic tradeoff between competitive ability if ungrazed (height) and ability to recover from grazing (growth rate). There was no height-growth rate relationship under nitrogen addition rates similar to field mineralization rates. In addition, faster-growing, shorter plants tended to have relatively higher above-ground growth rates than slower-growing, taller plants. These results suggest that natural selection has maintained a gradient of morphologies within this species ranging from short, rapidly growing genotypes adapted to intense grazing conditions to tall, slow-growing, grazer-susceptible genotypes that are superior light competitors in absence of herbivory.

The Influence of Carbon Dioxide and Daily Photon-flux Density on Optimal Leaf Nitrogen Concentration and Root: Shoot Ratio

Using a cost-benefit model, the leaf nitrogen concentration and root : shoot ratio that maximize whole-plant relative growth rate are determined as a function of the above-ground environment (integrated daily photon flux density and the concentration of carbon dioxide at the site of fixation within the leaf). The major advantage of this approach is that it determines the adaptive significance of leaf physiology by considering the functional integration of leaves and roots. The predicted response to increasing daily photon flux densities is an increase in optimal leaf N concentration (Nopt) and a concomitant increase in root: shoot ratio. Increased carbon dioxide concentrations, on the other hand, reduce Nopt and only slightly change root: shoot ratio. The observed increase in leaf nitrogen concentration found in plants growing at high altitudes (low CO2 partial pressure) is also predicted. Since these responses to light and CO2 maximize the whole-plant relative growth rate, the observed adjustments that plants make to light and carbon dioxide concentration appear to be adaptive. We show that the relationship between photosynthesis and leaf nitrogen concentration is complex and depends on the light and CO2 levels at which photosynthesis is measured. The shape of this function is important in determining Nopt and the opposite response of leaf nitrogen to light and carbon dioxide is shown to be the result of the different effects of light and CO2 on the photosynthesis-leaf nitrogen curve.