Root Partitioning Research Articles

Modelling Water in Crops and Plant Ecosystems

A water submodel is described that is specifically designed for use with plant growth simulators that represent internal plant substrates and variable shoot:root partitioning. The model calculates water flow from soil to root, root to shoot, and shoot to the atmosphere, for a closed-canopy situation. As presented here, the model has three state variables: the masses of water in the soil, root and shoot, and represents the processes of evapotranspiration, rainfall interception and evaporation from the canopy, and drainage. The Penman –Monteith equation is used for crop transpiration. The fluxes of water from soil to root, and root to shoot, are driven by water potential difference. Tissue water potential and its components are calculated from tissue water content and other plant variables and parameters. The model is able to simulate osmoregulation and describes a variable relationship between tissue water potential, its components and relative water content, depending on growth conditions. The model has elsewhere been integrated with two plant ecosystem models: for grassland and forest. The specific implementation and simulations given are for the Hurley pasture model (Thornley and Verberne, 1989), a temperate grass vegetative growth model. The model gives reasonable predictions for diurnal changes in water potential, drying-down behaviour and other quantities within the scope of the model.

Root and shoot growth, assimilate partitioning and cell proliferation in roots of sitka spruce ( Picea sitchensis) grown in filtered and unfiltered chambers

Rooted cuttings of clonal Sitka spruce ( Picea sitchensis (Bong.) Carr.) were grown from April to October in 1 m long tubes sunk into the ground inside open top chambers. The same experiment was repeated in each of two consecutive years using a different clone of Sitka spruce each year. Air was either passed directly into the chambers (ambient air) or passed over charcoal filters which removed the majority of gaseous pollutants before entering the chambers (filtered air). Ambient pollution did not appear to influence the growth of Sitka spruce at least over the experimental period used. No significant differences were found between plants exposed to ambient or filtered air in terms of shoot and root dry mass, needle dry mass, root length, carbohydrate content of roots and needles, and in the percentage of meristematic cells close to the apex in each phase or interphase or undergoing mitosis.

Carbon partitioning in Pinus radiata stands in relation to foliage nitrogen status.

First rotation Pinus radiata D. Don trees were grown on a nitrogen-deficient sand dune in an experimental design that included lupin (Lupinus arboreus Sims) as an understory species, and biennial application of balanced fertilizer in a replicated split-plot factorial design with thinning treatments as subplots. From an initial 2222 stems ha(-1), stands were thinned to 1483 and 741 trees ha(-1) at ages 2 and 4 years, respectively. Mean annual production of foliage, branches, stem, coarse roots, and cones was estimated from measurements of the dry matter content at ages 7, 10, 11 and 17 years. A model was used to estimate total above- and belowground dry matter production from measurements of leaf area index and foliar nitrogen concentration. An estimate of fine root production was obtained from the difference between the model estimate of total production and the estimate of aboveground production. The fertilizer and lupin treatments increased foliage nitrogen concentration, leaf area index and dry matter production of most aboveground components. In unthinned stands, foliage production ranged from 3 to 6 Mg ha(-1) year(-1), branch production from 1 to 4 Mg ha(-1) year(-1), and stem production from 8 to 19 Mg ha(-1) year(-1), depending on site fertility. Partitioning of aboveground production to foliage, branches, stems, and cones changed with tree age but it was not significantly influenced by the treatments. The fractions of aboveground dry matter production partitioned to foliage, branches, stems and cones were 0.23, 0.12, 0.63 and 0.02, respectively, for trees between ages 7 and 11 years, and 0.21, 0.08, 0.67 and 0.04, respectively, for trees between ages 11 and 17 years. With increasing foliage nitrogen concentration, partitioning to branches increased significantly, whereas partitioning to stems decreased. The fraction of total dry matter production partitioned to stems decreased significantly with thinning from 0.40 to 0.27 with a concomitant increase in the fraction partitioned to fine roots from 0.31 to 0.46. The average fraction partitioned to fine roots was 0.46 and 0.30 in unfertilized and fertilized stands, respectively. Stem production was more highly correlated with fine root partitioning than with leaf area index. Fine root production was not significantly affected by fertilizer application. The ratio of total net primary production to leaf area index increased significantly with thinning, but not with site fertility or stand age. The ratio of aboveground dry matter production to leaf area index increased with stand age and with the application of fertilizer but not with thinning.

Fibrous Root Growth and Partitioning in Smooth Root Sugarbeet Versus Standard Root Types

A greenhouse experiment with controlled lighting, temperature, moisture, and nutrients was conducted to compare the development of the fibrous root system for a smooth root (SR) sugarbeet genotype with that of four other diverse variety/ genotypes having standard grooved root architecture. Comparisons also included partition­ ing of photosynthate to leaf blade, petiole, taproot, and fibrous root for the five variety/ genotypes studied, and for their agronomic performance in a replicated field trial. The SR genotype produced the same ratio of taproot to fibrous roots as did the commercial hybrid variety 'Mono­ Hy E4.' There was a trend for fibrous roots of the SR line to develop lower on the taproot, farther from the crown, than in standard root types. The SR type had simHar leaf area, tap root/ leaf blade fresh weight ratio (TLWR), and. partitioning of photosynthate to leaf blades, petioles, taproots and fibrous roots as did the commercial varieties. The SR line was more closely aligned with the commer­ cial varieties in fibrous root growth and partitioning of photosynthate to plant parts than were the two other stan­ dard root type genotypes. From these greenhouse ex­ periments on fibrous root yield and partitioning, supported by agronomic field data, I conclude that the SR root type can produce enough fibrous roots to transport the required nutrients and water to allow yield comparable to standard root type sugarbeets.

Root and shoot dry matter partitioning in near-isogenic wheat lines differing in height

Increased wheat (Triticum aestivum L.) yields in most major cereal growing areas of the world have been associated with shorter cultivars which incorporate the Rht1 or Rht2 height-reducing alleles. Considerable uncertainty still exists, however, concerning the growth of vegetative tissues, especially roots, of these shorter genotypes. The objective of this study was to determine how dry matter (DM) partitioning, in vegetative shoot and root tissues, is related to plant height as determined by the number of Rht alleles present (tall (no Rht alleles), semidwarf (Rht1 or Rht2), dwarf (Rht1 and Rht2) within a common genetic background. Tall, semidwarf, and dwarf near-isogenic lines were studied within each of four diverse genetic backgrounds. Six controlled-environment experiments were carried out in which plants were grown in sand (nutrients applied hydroponically) and harvested following anthesis. Stem and shoot (total aboveground tissue) DM plant−1 increased with plant height. However, there was no relationship between plant height and root DM plant−1. Root/shoot ratios tended to be negatively correlated with plant height. Leaf blades and head DM plant−1 were not consistently related to plant height. In the absence of selection pressure, genotypes containing Rht alleles should have root DM comparable to their tall counterparts, and root/shoot ratios equal to, or greater than, their tall counterparts. The Rht alleles also decreased individual leaf blade areas, primarily through effects on leaf length, and increased stomatal frequencies of early leaves; effects on the flag and penultimate leaves were ambiguous, suggesting that the gibberellic acid (GA3) intensitive Rht alleles exert greater control during earlier growth stages. Key words: Height-reducing alleles, plant height, tall, semidwarf, dwarf

Comparison of Plant Establishment Method, Transplant, or Direct Seeding on Growth and Yield of Bell Pepper

Transplants produced with overhead or subirrigation and plants from direct seeding using primed or nontreated `Jupiter' bell pepper (Capsicum annuum L.) seeds were evaluated for growth and yield in the field for 3 years. Early in development, overhead-irrigated (01) transplants had more basal root elongation than subirrigated (SI) transplants; however, root growth differences caused by irrigation systems in the greenhouse were minimized during late ontogeny in the field. Basal, lateral, and taproot dry weights accounted for 81%, 15%, and 4% of the total for transplants and 25%, 57%, and 18% of the total for direct-seeded plants. Direct-seeded plants maintained a more-balanced root, stem, leaf, and fruit dry matter partitioning than transplants, which allocated more dry weight (per unit of root growth) to stems, leaves, and fruits. Over all seasons, transplants exhibited significantly higher and earlier yields than direct-seeded pepper plants, and total yields were similar between SI and OI transplants and between primed and nontreated seeds.

Absorption, Translocation, and Metabolism of Clomazone, Metribuzin and Linuron in Soybean (Glycine max) and Common Cocklebur (Xanthium strumarium)

Research was conducted in soybean and common cocklebur to determine if the synergistic interactions of clomazone plus metribuzin and clomazone plus linuron were due to the effect of one herbicide on root uptake, partitioning, or metabolism of the other. Treatments consisted of14C-clomazone alone and combined with metribuzin or linuron,14C-metribuzin alone and combined with clomazone, and14C-linuron alone and combined with clomazone. Root uptake and partitioning of clomazone applied alone in soybean differed compared to clomazone plus metribuzin. Root uptake and partitioning of metribuzin or linuron did not differ when applied alone or combined with clomazone. Binding of clomazone or its metabolites in an unextractable form may be a method of deactivating clomazone by soybean, but not by common cocklebur. Levels of parent clomazone were higher in common cocklebur roots when clomazone was combined with metribuzin and linuron compared to clomazone done. Levels of parent metribuzin were higher in soybean roots, and in common cocklebur roots and shoots when clomazone was combined with metribuzin compared to metribuzin alone. Levels of parent linuron were greater in soybean shoots when linuron was applied with clomazone compared to linuron alone. These results indicate that the metabolism of metribuzin and linuron is altered in both species when clomazone is applied, leading to increased phytotoxicity.

Growth and shoot:root partitioning of spinach plants as affected by nitrogen supply

ABSTRACTSpinach plants (Spinacia oleracea L.) were grown hydroponically in fixed environmental conditions either at full nitrate availability (11·8mol m‐3) or at a suboptimum relative nitrate addition rate of 0·20d‐1, 0·15d‐1 or 0·10d‐1 respectively, the other nutrients being adequately provided. The relative growth rate (RGR) of the plants varied significantly with the nutrition treatment and decreased during development in all treatments. The concentration of reduced nitrogen in the plants grown at full nitrate availability did not change significantly during the experimental growth period and nitrate accumulation was substantial. After an adaptation period, the concentration of reduced nitrogen in the plants at the suboptimum nitrate addition rates increased during growth and was lowest at the lowest relative nitrate addition rate. Nitrate uptake was almost complete in the suboptimum treatments and nitrate accumulation was negligible as long as the concentration of reduced nitrogen was below 2·0 mmol (g dry weight)‐1. The RGR of all plants was proportional to the concentration of reduced nitrogen in the plant minus a minimal tissue concentration required for growth. However, the proportionality factor was inversely related to the plant mass. This relationship was summarized in an empirical model which explained 98·7% of the variance of the dry weight (log scale) data of all treatments at all harvests. The model was compared with other growth models found in the literature. The shoot/root weight ratio increased from 2 to 4 if nitrate provision was not limiting, and initially, this ratio decreased at suboptimum nitrate provision but increased at higher growth stages. Possible explanations of the dynamics of dry matter partitioning are discussed in relation to models.

Aluminum Partitioning in Intact Roots of Aluminum-Tolerant and Aluminum-Sensitive Wheat (Triticum aestivum L.) Cultivars

Aluminum (Al) partitioning in intact roots of wheat (Triticum aestivum L.) cultivars that differ in sensitivity to Al was investigated. Roots of intact seedlings were exposed to Al for up to 24 hours and distribution of Al was assessed visually by hematoxylin staining or by direct measurement of concentration of Al by atomic absorption spectrophotometry or ion chromatography. Major differences in Al accumulation between Al-tolerant (Atlas 66) and Al-sensitive (Tam 105) cultivars were found in the growing regions 0 to 2 and 2 to 5 millimeters from the root apex. Al content was 9 to 13 times greater in the 0 to 2 millimeters root tips of cv Tam 105 than in the tips of cv Atlas 66 when exposed to 50 micromolar Al for 19 to 24 hours. The oxidative phosphorylation inhibitor carbonyl cyanide m-chlorophenylhydrazone and the protein synthesis inhibitor cycloheximide increased Al uptake by intact root tips of cv Atlas 66. Also, loss of Al from the roots of both cultivars was measured after the roots were "pulsed" with 50 micromolar Al for 2 hours and then placed in an Al-free nutrient solution for 6 hours. The 0 to 2 millimeter root tips of cv Tam 105 lost 30% of the absorbed Al, whereas the tips of cv Atlas 66 lost 60%. In light of these results, we conclude that the differential Al sensitivity in wheat correlates with the concentration of Al in the root meristems. The data support the hypothesis that part of the mechanism for Al tolerance in wheat is based on a metabolism-dependent exclusion of Al from the sensitive meristems.

Root Growth and Partitioning of 13C-labelled Photosynthate in the Seminal Root of Corn Seedling as Affected by Light Intensity.

The effects of shading on growth and allocation pattern of photosynthate in the seminal root of corn seedlings were studied using 13C as a tracer. Corn seedlings, preshaded for 2 days (light intensity was reduced to 57% or 25% of nonshaded plants), were fed with <13>C-labelled CO2 for 2 h under given light conditions, then allowed to grow for the subsequent 3 days. The extension rate of the seminal axis was not affected by shading. The total number and length of laterals were reduced by shading, while a marked increase of number and length of laterals was observed in the specific region within 10 cm from the apex of shaded plants. The 13C allocation to the laterals of the seminal root was reduced by shading ; in contrast, allocation was increased in the seminal axis. The decrease of 13C allocation to the laterals was associated with the reduction of the development of laterals. The increase of 13C allocation to the seminal axis was due to a marked accumulation of 13C in the root tip and axis within 10 cm from the apex, and this accumulation was strongly associated with the enhancement of the growth of laterals and the extension of the axis that occurred in the same region.

The effects of prior exposure to sulphur dioxide and nitrogen dioxide on the water relations of timothy grass ( Phleum pratense) under drought conditions

Studies of the growth and water relations of the grass Phleum pratense L. (Timothy) were made after simultaneous exposure to SO 2 and NO 2 at concentrations ranging from 80 + 57·4 μg m −3 to 240 + 172 sd2 μg m −3 (SO 2 + NO 2). Decreased partitioning to the roots was evident during exposure to the pollutants, but when the plants were returned to clean air restrictions in root growth did not persist. Shoot to root partitioning was, however, complicated by the additional factor of changes in the nutritional status of the soil after additional columns of fresh soil were attached to the original tubes. The rate of use of soil water was nevertheless substantially increased by the pollution treatment and after a period of 23 days in which water was withheld, a clear pollution × water stress interaction was seen. The ability of polluted leaves to conserve water under severe water stress was tested by excising the leaves and measuring their water loss over time. The results from this second experiment showed that conservation of water by the leaves was appreciably affected after exposure to 80 + 57·4 μg m −3 or 133·3 + 95·6 μg m −3 SO 2 + NO 2. It seems likely that damage to the cells in the epidermal layer, leading to malfunctioning of stomata, is mainly responsible for the reduced ability to conserve water under conditions of extreme stress.

Root Uptake and Partition of Copper, Iron, Manganese, and Zinc in Pinus radiata Seedlings Grown under Different Copper Supplies

Summary In spite of the low Cu needs, a Cu2+ level of 0.03 µM in hydroponic cultures of Pinus radiata seedlings induces a Cu-deficient situation; under these conditions the foliar Cu was 4 mg·kg-1 dry wt after 2.5 months growth, which decreased to 1 mg kg-1 in 5-month-old seedlings. This is shown by a decrease of the growth rate with time, which appears negligible between 7.5 and 9 months in culture. The Cu content of roots, foliar and non-foliar stems, and leaves increases with the micronutrient concentration in the culture solutions, but the response of each organ is inversely related with its distance from the hydroponic medium. In any case P. radiata seedlings showed a very efficient Cu2+ absorption capability of the root, but the nutrient translocation to the aerial organs appears restricted, maybe as a protection mechanism. Until 7.5 months in culture the optimum plant development occurs under excess Cu2+, which shifts to normal Cu2+ levels after 9 months growth; this can be explained as a transient Cu deficiency during the first developmental stage. Mn absorption showed some type of antagonism with that of Cu2+, the needles being the site of the highest Mn concentration in pine. On the contrary, the rate of Fe absorption increases with Cu2+ levels, but the translocation to stems and leaves occurs very slowly. Zn showed a Z-shape partition pattern along root, stems, and needles, with the highest concentrations in root and foliar stem; in addition, Zn absorption appears to be antagonistic to that of Cu.

A Model of Shoot: Root Partitioning with Optimal Growth

A Model of Shoot: Root Partitioning with Optimal Growth

Comparison of Two Shoot—Root Partitioning Models with Respect to Substrate Utilization and Functional Balance

A transport resistance model for shoot—root partitioning by Thornley and a more aggregated partitioning model by Reynolds and Thornley are compared. Three functional forms of substrate utilization are applied, corresponding to different assumptions on the ability of carbon and nitrogen to compensate one another in promoting structural growth. On the basis of simulations at balanced exponential growth, it is shown that the Reynolds and Thornley model (in optimal form) is embedded in the Thornley model. Davidson's functional balance is studied as a function of the degree of carbon-nitrogen compensation. The applicability of the models and the utilization functions is discussed.

A Model of Assimilate Partitioning and Utilization in Shoots and Roots in the Vegetative Stage ofLolium multiflorum

Abstract With the purpose of improving crop growth simulation, a mechanistic model and its parameters for assimilate partitioning and utilization were developed for vegetative Lolium multiflorum Lam. (cv. Lomi). The model is based on first-order kinetics and on previously determined efficiencies of assimilate utilization. The driving variable is gross photosynthesis. The five state variables are the translocation pool of recently assimilated carbon, and for shoots and roots, the storage pools and the pools of structural material, respectively. The model consists of first-order rate equations with six parameters. These parameters were estimated by analysis of the time course of CO2-exchange rates, separately for shoots and roots, respectively, during prolonged dark periods of two days and prolonged photo-periods of two days. The analysis was based on maintenance coefficients and on utilization efficiences of shoots and roots and on simulation. Due to the differences in carbon utilization between shoots and...

EFFECTS OF LOCALIZED AND OVERALL WATER STRESS ON ASSIMILATE PARTITIONING IN BARLEY BETWEEN SHOOTS, ROOTS AND ROOT EXUDATES

SUMMARYPolyethylene glycol 4000 (PEG) at an osmotic potential of −0.3 MPa had no effect on uptake of 14CO2 and partitioning between shoots and roots in barley. When an osmotic potential of −0.8 MPa was applied to the upper zone of the root system, total 14CO2 uptake and partitioning were unaffected but assimilate accumulated in the tips of nodal roots exposed to PEG. There was a parallel accumulation of soluble sugars. Transport of assimilates to the seminal root system declined. Exudation of soluble, labelled compounds by the roots was markedly diminished. When PEG was supplied to the upper root zone at −0.8 MPa and the lower zone at −0.6 MPa total 14CO2 uptake and assimilate transport declined, but there was still some accumulation of labelled compounds and soluble sugars in the nodal root tips and root exudation was diminished. The results are discussed in relation to assimilate partitioning, growth and osmotic adjustment in nodal roots.

Translocation of 14C‐labelled photoassimilates to roots in barley: effects of mildew on partitioning in roots and the mitotic index

First leaves of barley seedlings grown in solution culture were inoculated with powdery mildew when the second leaf was fully emerged. 14C‐labelled carbon dioxide was fed to either first or second leaves of infected and non‐infected plants. Translocation of labelled photoassimilates into roots, and partitioning into soluble, storage and structural fractions were studied in tip, mid and basal regions of primary roots 24 h after feeding. Mildew reduced the total activity in the plant, but had little effect on assimilate distribution since the percentage activity translocated to roots was only transiently reduced, approximately 7 days after infection. Reduced import led to a reduction in the specific activity of different fractions within roots, reductions being greatest in root tips. These changes were similar whichever leaf was fed. Changes in specific activity became progressively more pronounced in the 10 days following infection, and were paralleled by a reduction in the mitotic index of root tips. It is concluded that meristematic activity, and thus the growth, of primary roots of barley is particularly sensitive to reductions in photoassimilation caused by powdery mildew infection.