Unit Root Dry Weight Research Articles

The role of root size and root efficiency in grain production, and water-and nitrogen-use efficiency in wheat.

The root system is the major plant organ involved in water and nutrient acquisition, influencing plant growth and productivity. However, the relative importance of root size and uptake efficiency remains undetermined. A pot experiment was conducted using two wheat varieties with different root sizes to evaluate their capacity for water and nitrogen (N) uptake and their effects on grain production, water-use efficiency (WUE), and N-use efficiency (NUE) under two water treatments combined with three N levels. The leaf water potential and root exudates of changhan58 (CH, small root variety) were higher or similar to those of changwu134 (CW, large root variety) under water/N treatment combinations, indicating that small roots can transport enough water to above the ground. The addition of N improved plant growth, photosynthetic traits, and WUE significantly. There were no significant differences in WUE or grain production between the two cultivars under well-watered conditions. However, they were significantly higher in CH than in CW under water deficit stress. Nitrogen uptake per unit root dry weight, glutaminase, and nitrate reductase activities were significantly higher in CH than in CW, regardless of moisture conditions. Root biomass was positively correlated with evapotranspiration, while the root/shoot ratio was negatively correlated with WUE (P < 0.05) but not with NUE. In a pot experiment, water and N uptake were more strongly associated with resource uptake availability than root size. This may provide guidance in wheat breeding programs for drought-prone regions. © 2023 Society of Chemical Industry.

Study on the Relationship of Root Morphology and Phosphorus Absorption Efficiency With Phosphorus Uptake Capacity in 235 Peanut (Arachis hypogaea L.) Germplasms

Peanut (Arachis hypogaea L.) is a significant oil and protein crop. Its yields greatly depend on the availability of phosphorus (P). Root morphology and P absorption efficiency are important factors affecting the P uptake capacity, but their relationships in peanuts are rarely reported. Here, we report the effect of root morphology and P absorption efficiency on the P uptake capacity in peanuts using 235 germplasms. In this work, we use the P uptake rate per plant to reflect the P uptake capacity. The P uptake capacity was significantly increased after low-P treatment and showed great differences among the germplasms. The germplasms with higher P absorption efficiency and a well-developed root system have higher P uptake capacity. Under both P conditions, the P absorption efficiency plays more important roles than root morphology in P uptake capacity, and the P uptake rate per unit root dry weight and the P uptake rate per unit root surface area contributed the most. Root morphology contributes more to the P uptake capacity under low-P treatment than under sufficient-P conditions, and root surface area contributed the most. Forty-eight germplasms with higher P uptake capacity were screened, and they had three different uptake strategies under low-P treatment. These findings indicated that low-P stress induces root growth and improves the P absorption efficiency of peanuts to ensure the plant gets enough P; provides new insights into the relationship between the P uptake capacity, P absorption efficiency, and root morphology; and furnishes important evaluation indexes for high P-efficient germplasm selection.

Trade-Off between Root Efficiency and Root Size Is Associated with Yield Performance of Soybean under Different Water and Phosphorus Levels

(1) Background: Root traits play important roles in acclimating to water and phosphorus (P) shortages. However, the relative importance of root size and efficiency under these conditions is unknown. (2) Methods: This study investigated the role of root size and efficiency in acclimating to water- and P-limited environments. Three soybean genotypes with contrasting root sizes were grown in tall cylindrical pots to compare grain yield, root density, and water- and nutrient-uptake efficiencies under two water (well-watered and water-stressed) and three P levels (0 (P0), 60 (P60), and 120 (P120) mg P kg−1 dry soil). (3) Results: Water or P deficit, and combined water and P deficit significantly decreased grain yield, which was associated with greater P uptake per unit root dry weight (DW) under water stress. The genotype Zhonghuang 30 (ZH) with the greatest water, nitrogen, and P uptakes per unit root DW had the highest grain yield at P60 and P120 under water stress and P0 under well-watered conditions, but ZH had the lowest grain yield at P60 and P120 under well-watered conditions, due to its small root size. (4) Conclusions: High root efficiency—which was correlated with high root density—improved grain yield under P- and water-limited conditions, but restricted yield potential when P and water were not limited.

Growth and Betacyanin Content of Beetroots (Beta vulgaris L.) Under Water Deficit in A Tropical Condition

The present study, a part of a series of studies carried out to explore the possibility of beetroot cultivation in the tropics on highlands, was designed to investigate the growth and betacyanin content of beetroot plants in response to water deficit in a tropical condition. The water deficit was executed through varied watering intervals consisting of once three (as control), four, five, six and seven days. A randomized block design with five replicates was used to impose the treatments. The effect of water deficit was found to reduce the leaf water content, the biomass production (total dry weight) and the root yields of beetroot plants. Root dry weight decreased by more than 20% and 50% with the watering interval once four and seven days respectively compared with that once three days. The betacyanin content of roots was not influenced by the water deficit when expressed per unit volume of fresh root extracts (340.5 ± 60.1 mg/l), and increased when expressed per unit root dry weight. It is suggested that an optimal supply of water, for instance watering once three days, is necessary to obtain beetroot plants growing optimally and producing a high root yield and betacyanin content of roots.

Nitrogen fertilization alters the distribution and fates of photosynthesized carbon in rice–soil systems: a 13C-CO2 pulse labeling study

Although nitrogen (N) fertilization is widely used to increase rice yield, its impact on the distribution, transformation, and fates of photosynthetic carbon (C) in rice–soil systems is poorly understood. To address this, we quantified the C flows into various pools in a rice–soil system. Rice (Oryza sativa L.) was pulse-labeled with 13CO2 at the tillering stage. Samples were collected six times during the 26 days following labeling. We quantified the partitioned photosynthesized C into various pools using stable isotopic techniques and estimated C flows. Although the net distribution of assimilated C to belowground pools did not change, N fertilization promoted C assimilation in aboveground biomass. C allocation into soil was enhanced by N fertilization during early growth, but decreased during late growth. N fertilization induced higher mass-specific rhizodeposition (per unit root dry weight) and its turnover rate compared with the unfertilized system. However, with higher microbial turnover, the daily C allocation from roots to soil was similar at both fertilization levels. Although total C input into soil is enhanced by N fertilization, its further fate is N fertilization independent, thus leading to a net accumulation of C input in rice paddy soil similar to that observed unfertilized soil.

Genotypic Variation in Biomass Production at the Early Vegetative Stage among Rice Cultivars Subjected to Deficient Soil Moisture Regimes and Its Association with Water Uptake Capacity

ReferencesGenetic improvement in water uptake ability and/or water use efficiency (WUE) of rice cultivars is one option to enhance productivity under water-limited conditions. We examined the genotypic variation in biomass production among 70 rice cultivars (69 cultivars of NIAS global rice core collection and Azucena) under different soil moisture conditions, and to identify whether water uptake ability or WUE is responsible for the variation, if any. Two-week-old seedlings were transplanted into pots and grown for three weeks in an environmentally-regulated growth chamber under three soil moisture regimes: flooded (−0.02 MPa soil water potential) and two unflooded (−0.10 and −0.52 MPa) conditions. Substantial genotypic variations in total dry weight (TDW) were observed under all three regimes. Among all the cultivars tested, TDW was significantly correlated with water uptake ability, but not with WUE. However, several cultivars exhibited comparably higher WUE while showing superior biomass production under the −0.52 MPa regime. The amount of water uptake was significantly correlated with root dry weight among cultivars regardless of moisture regimes, while substantial genotypic difference in the amount of water uptake per unit root dry weight was observed. These results indicate that a marked genotypic difference exists in biomass production at the early vegetative growth under water-deficient conditions, and that this difference appears to be ascribed primarily to greater water uptake capacity, and additionally to higher WUE in drought-tolerant cultivars.

Interactive Effects of Elevated Atmospheric CO2 and Waterlogging on Vegetative Growth of Soybean (Glycine max (L.) Merr.)

Waterlogging is a major predicted agricultural problem for crop production in some areas under current climate change, but no studies are available on the interactive effects of waterlogging and elevated atmospheric CO2 concentration ([CO2]). We hypothesized that elevated [CO2] could alleviate the damage caused by waterlogging, and tested the hypothesis using vegetative growth of soybean (Glycine max) in 10 experiments (different sowing time and different soil type) conducted at Morioka and Tsukuba for three years. The 2-week-old plants grown under elevated and ambient [CO2] were exposed to waterlogging for 2 weeks. Total dry weight at the end of the treatment was higher under elevated [CO2] than under ambient [CO2], and it was significantly reduced by waterlogging under both levels of [CO2], without significant [CO2]×waterlogging interactions, at both locations. The negative effects of the waterlogging were greater in root dry weight than in top dry weight, and the root exudation per unit root dry weight was also reduced by waterlogging, without a [CO2] ×waterlogging interaction. Therefore, the hypothesis of a [CO2]×waterlogging interaction can be rejected, and provide an important basis for predicting future damage caused by waterlogging under elevated [CO2] conditions.

Soil compaction–N interactions in barley: Root growth and tissue composition

A controlled environment study investigated the interactions between soil compaction and N availability on the growth and root tissue composition of young barley plants. Plants were grown for 14 days in a mixture of sand and calcined clay (fired clay granules) at two levels of compaction (low and high; dry bulk densities of 0.94 and 1.08 g cm −3 respectively) and two levels of N supply (high, resulting in N sufficient plants and low giving plants deficient in N). High compaction reduced total root length by 23%, leaf area by 21% and altered biomass partitioning (reduced leaf area ratio and increased root weight ratio), but had no effect on total biomass production over the time-course of the experiment. By contrast low N supply, reduced root biomass by 42% and shoot biomass by 47%, but had less effect on shoot morphology than compaction. There was no significant interaction between compaction and N supply on growth and biomass partitioning, although towards the end of the experiment, the rate of N uptake per unit root dry weight was reduced by about 50% by high compaction when N supplies were low, but not when they were high. Compaction altered the concentration of some root tissue components independently of N supply. For example, high compaction reduced the concentration of cellulose plus hemi-cellulose by 30% and increased the mineral content by 38%, whilst N supply had no effect. The concentration of several other components was altered by compaction and N supply in the same direction. Both high compaction and low N supply increased the lignin concentration whilst reducing the concentration of organic N compounds and nitrate, thereby increasing the C:N and lignin:N ratios. Compaction and low N supply increased C:N by a factor of 1.3 and 1.8 respectively, whilst the lignin:N ratio was increased by 1.7 and 2.1 respectively. Thus, both compaction and low N availability altered root tissue composition in a way that might reduce the rate of root degradation by soil microbes. The implications of these findings for modelling nutrient cycling are briefly discussed.

Mechanism of Tolerance to Potassium Deficiency Between Liaomian 18 and NuCOTN99B at Seedling Stage

The objective of the present study was to elucidate the mechanism of tolerance to potassium (K) deficiency in cotton ( Gossypium hirsutum L.) through comparing the differences of K uptake, translocation, and utilization in a K-efficient cultivar Liaomian 18 (non-Bt cotton) and a K-inefficient cultivar NuCOTN99B (American Bt cotton). The seedlings of the 2 cultivars were hydroponically cultured in a growth chamber and treated with sufficient K of 2.5 mmol L −1 (control) or deficient K of 0.03 mmol L −1. There was no significant difference in dry matter yield of seedlings between both cultivars under the control condition, whereas Liaomian 18 produced 170% more dry matter than NuCOTN99B in the K-deficient solution. Under the K-deficient condition, the amounts of K uptake per unit root dry weight, per unit root length, and per unit root surface area in Liaomian 18 were similar to or lower than those in NuCOTN99B, and the ratio of K accumulation in leaf to that in whole plant was 57.7% and 67.6% in Liaomian 18 and NuCOTN99B, respectively. These results indicated that the higher K-efficiency of Liaomian 18, compared with NuCOTN99B, was independent of its capacities for root physiological uptake and translocation of K to leaf. In contrast, Liaomian 18 had larger root system than NuCOTN99B, and its root length, root surface area, and root volume were 3.4, 3.8, and 4.2 folds higher than those of NuCOTN99B, respectively. In addition, the K utilization index (dry matter produced per unit of K concentration) in Liaomian 18 was 147% higher than that in NuCOTN99B. Therefore, the higher tolerance to K deficiency in Liaomian 18 possibly depended on its larger root system and greater internal K utilization efficiency. On account of the insignificant differences in osmotic potential and relative water content in leaf between Liaomian 18 and NuCOTN99B, the higher internal K utilization efficiency of Liaomian 18 was deduced to be associated with the biochemical function of K rather than the biophysical function of K.

Seasonal changes in the effects of free‐air CO2 enrichment (FACE) on growth, morphology and physiology of rice root at three levels of nitrogen fertilization

AbstractOver time, the relative effects of elevated [CO2] on the aboveground photosynthesis, growth and development of rice (Oryza sativa L.) are likely to be changed with increasing duration of CO2 exposure, but the resultant effects on rice belowground responses remain to be evaluated. To investigate the impacts of elevated [CO2] on seasonal changes in root growth, morphology and physiology of rice, a free‐air CO2 enrichment (FACE) experiment was performed at Wuxi, Jiangsu, China, in 2002–2003. A japonica cultivar with large panicle was exposed to two [CO2] (ambient [CO2], 370 μmol mol−1; elevated [CO2], 570 μmol mol−1) at three levels of nitrogen (N): low (LN, 15 g N m−2), medium (MN, 25 g N m−2) and high N (HN, 35 g N m−2). Elevated [CO2] increased cumulative root volume, root dry weight, adventitious root length and adventitious root number at all developmental stages by 25–71%, which was mainly associated with increased root growth rate during early growth period (EGP) and lower rate of root senescence during late growth period (LGP), while a slight inhibition of root growth rate occurred during middle growth period (MGP). For individual adventitious roots, elevated [CO2] increased average length, volume, diameter and dry weight early in the season, but the effects gradually disappeared in subsequent stages. Total surface area and active adsorption area per unit root dry weight reached their maxima 10 days earlier in FACE vs. ambient plants, but both of them together with root oxidation ability per unit root dry weight declined with elevated [CO2] during MGP and LGP, the decline being larger during MGP than LGP. The CO2‐induced decreases in specific root activities during MGP and LGP were associated with a larger amount of root accumulation during EGP and lower N concentration and higher C/N ratio in roots during MGP and LGP in FACE vs. ambient plants. The results suggest that most of the CO2‐induced increases in shoot growth of rice are similarly associated with increased root growth.

The relationship of hydraulic conductance to root system characteristics of peach (Prunus persica) rootstocks

Specific rootstocks can differentially influence the vegetative growth and development of fruit trees. However, the physiological mechanism involved in this phenomenon has been elusive. Recent research comparing different peach (Prunus persica L. Batsch) rootstocks suggests that the rootstock effect on vegetative growth in peach trees is associated to water relations and more specifically to differences in rootstock hydraulic conductance. This study was intended to confirm differences in hydraulic characteristics of similar size peach trees grafted on different rootstocks and to examine root system characteristics that could be associated with rootstock hydraulic limitations. Trees on rootstocks that were known to have a size‐controlling effect when grown under field conditions had lower rootstock conductance than trees on the vigorous (control) rootstock when rootstock hydraulic conductance was measured with both the high‐pressure and evaporative flow methods. Rootstocks with the lowest hydraulic conductance had less fine root surface area and length per unit root dry weight than the more vigorous (control) rootstock. However, contrary to previous field studies, in this study there were no significant differences in dry matter production and distribution among trees on the different rootstocks suggesting that whatever the normal growth control mechanism was, it did not differentially influence growth under the specific conditions of this study. This research confirmed that peach rootstocks exhibiting size‐controlling behavior under field conditions differed in their hydraulic and morphological characteristics under controlled growth conditions even when those growth conditions negated the expression of the size‐controlling behavior.

Genetic dissection of silicon uptake ability in rice (Oryza sativa L.)

The adequate presence of silicon (Si) in rice plants can enhance their yield and improve their tolerance to various biotic and abiotic stresses. In this study Si uptake abilities were compared between the japonica rice cultivar (cv.) Kinmaze and the indica rice cv. DV85 under three Si concentrations (0.16, 0.4, and 1.6mM) at different time points from 1 to 12h. The results showed that the phenotypic values of two traits—Si uptake by individual plants (SP, Si uptake by all roots of a plant) and Si uptake per unit root dry weight (SR=SP/root dry weight)—of Kinmaze were significantly higher than those of DV85 (P<0.01). Meanwhile, a kinetic study indicated that the Si transporters in Kinmaze and DV85 had the same affinity for silicic acid, but with different Vmax values, indicating that Kinmaze had more Si transporters in the roots than DV85. This may be the main reason for the difference in Si uptake ability between Kinmaze and DV85. In addition, a mapping population consisting of 81 recombinant inbred lines (RILs) derived from the cross between Kinmaze and DV85 was used to detect quantitative trait loci (QTLs) underlying SP and SR. The RILs follow a continuous one-peak distribution and show transgressive segregation in both directions for SP, SR, and root dry weight (RDW). Three QTLs for SP, four for SR, and three for RDW were detected. This can explain 7.16–17.15% of the phenotypic variation (PVE). Thus, the results obtained in this study provide a better understanding of the mechanism of rice Si uptake ability and the basis for fine-mapping the genes involved.

Nitrogen absorption by roots as a cause of interspecific variations in leaf nitrogen concentration and photosynthetic capacity

Summary Optimal biomass allocation models predicted that an increase in specific absorption rate (SAR: nitrogen absorption rate per unit root dry weight) increases the optimal leaf N concentration (LNC) which maximizes whole‐plant growth rates. From this prediction, we hypothesized that inherent differences in the N absorption ability of roots, which is represented by differences in SAR, causes interspecific differences in LNC and photosynthetic capacity (Pmax). Four deciduous tree species and three herb species were grown under controlled conditions to test this hypothesis. Despite growing under the same soil N conditions, the SAR of these species differed more than sixfold, with the deciduous trees having a smaller SAR than the herbs. Consistent with the hypothesis, there were strong positive correlations between SAR, LNC and Pmax. Leaf dry mass per area and the LNC–Pmax relationship, factors correlated with leaf life span, differed little among the species, suggesting a small effect of differences in these properties on the variation in LNC. Simulations were performed using an optimal biomass allocation model and parameter values determined from measurements of each species. These demonstrated that the observed variation in LNC could be explained largely by differences in the N absorption ability of the species. Additionally, the causal relationship between N absorption ability and LNC, suggested by optimal biomass allocation models, was verified by manipulating the biomass allocation between roots and leaves of Morus bombycis using uniconazole, an inhibitor of gibberellin synthesis. These results indicate a close functional link between N absorption ability and LNC, which would account for large variations in LNC and Pmax across species.

N uptake, soil retention and loss of soil-applied 15NH415NO3 in young Fuji/M.26 apple trees with different N status

SummaryNitrogen (N) uptake, soil retention and loss of soil-applied N were studied in young apple trees with different N backgrounds. Bench-graft potted Fuji/M.26 (Malus domestica Borkh) trees were fertigated with 5, 10 or 20 mM N twice a week from June to August, and the trees were removed from soil and bare-root stored in a 2°C cold room in December of the first season. In April of the second season, the trees were washed and replanted in containers with a N-free medium (perlite:vermiculite=l:l v), and received 500 ml Hoagland’s nutrient solution without N weekly through the experiment. The trees received 15NH415NO3 at 1g per plant or no N on June 21. Four trees from each treatment were harvested at one, two and four weeks after 15N application, and 15N and total N in plant tissues and soil were analysed. N fertigation rates during the first growing season increased tree growth and N reserve levels, and N content in trees in the second year. New shoot and leaf growth in the following season was positively related to reserve N. 15N uptake increased during the four weeks after 15N application while soil 15N retention decreased. There was no significant difference in the total 15N uptake per tree. However, trees with the lowest N contents at the end of the first growing season had the highest rate of 15N uptake per unit root dry weight. Four weeks after application of 15N, tree uptake of N accounted for about 60% of applied 15N, while about 20% of the N still remained in the soil, and another 20% of the N was lost. Our results suggested that trees with lower N status are more efficient in N uptake from soil.

Root proliferation in perennial grasses of low and high palatability

Root proliferation of desirable (Stipa clarazii andS. tenuis) and undesirable (S.ambigua)perennial grasses was studied in semiarid rangelands of Central Argentina(40°39′S, 62°54′W) in 1998. On 17 September, soil coreswereremoved from the edge of the plant, metal structures lined with screen mesh(hereafter called bags) were buried in the holes, and root-free soil was placedinto these structures. Numbers of green tillers and circumference per plant hadpreviously been determined. Since plants were of unequal size among species,root length and root dry weight data are reported on a per green tiller basis.Half of the plants was defoliated to 5 cm stubble height on 17September and/or 12 October, while the other half remained undefoliated(controls). Bags were destructively harvested either 20 days after the firstdefoliation (first sampling) or 56 days after the second defoliation (secondsampling) by digging out soil very carefully around each bag. Roots were washedfrom soil, root length estimated by the line intercept method, root dry weightdetermined after oven-drying, and root length per unit root dry weightcalculated from the two measured variables. Root length and dry weight weremorethan 96% greater on defoliated and undefoliated plants ofS. clarazii than on those of S.tenuisor S. ambigua for both sampling dates. Root length perunitroot dry weight, however, was more than 43% greater (p < 0.05) inS. tenuis than in S. clarazii andS. ambigua during the second sampling. Defoliated plantshada similar root length and root dry weight than undefoliated plants in all threespecies, although plants of S. tenuis defoliated twiceshowed a greater (p < 0.05) root length than undefoliated controls. Rootlength and root dry weight were similar between sampling periods, except onundefoliated plants of S. tenuis which had a greater (p<0.05) root length and root dry weight at the first than at the second sampling.Although root length per unit root dry weight may be greater inS. tenuis than in S. clarazii andS. ambigua, greater root length and dry weight increasesinS. clarazii after defoliation appear determinant incontributing to explain its greater competitive ability and defoliationtolerance when compared with the other two species.Nomenclature of taxa followed.

Phosphorus acquisition from soil by white lupin (Lupinus albus L.) and soybean (Glycine max L.), species with contrasting root development

White lupin and soybean have contrasting root morphologies: white lupin develops proteoid or cluster roots, roots with discreet clusters of short, determinate branch roots (rootlets) while soybean develops a more fibrous root system with evenly distributed, longer branch roots. Growth and P acquisition by white lupin and soybean were compared in a soil high in bound, total P, with or without additional inorganic P applied in solution. Additional P increased biomass by 25% and doubled total P in soybean. In contrast, white lupin did not respond to additional P in biomass or total P. However added P decreased cluster development on proteoid roots indicating that white lupin sensed the added P. The reduction in cluster weight per plant was exactly countered by an increase in dry weight of other roots. Soybean root development responded to P application, proliferating branch roots with active meristems in the upper portion of the soil profile where P was applied, and reducing root weight to plant weight by 13%. White lupin did not proliferate roots in response to P application. When P was not added to soil, soybean and lupin acquired similar P per unit root dry weight. However, white lupin accumulated 4.8 times more P per unit root length, suggesting that P acquisition in these plants involved other mechanisms such as the exudation of P solubilizing compounds. Soybean accessed P by developing more root length thus colonising more soil volume than white lupin and, therefore, was better able to take advantage of the added P. Pericycle and root tip meristem activities were critical to the differences in root development between white lupin and soybean, and therefore their responses to plant and soil P.

Comparative response of wheat and oilseed rape to nitrogen supply: absorption and utilisation efficiency of radiation and nitrogen during the reproductive stages determining yield

We investigated the response of spring wheat and oilseed rape to nitrogen (N) supply, focusing on the critical period for grain number definition and grain filling. Crops were grown in containers under a shelter and treated with five combinations of applied N. Wheat and oilseed rape produced comparable amounts of biomass and yield when corrected for the costs of biomass synthesis (SC). From the responses of biomass and yield to late N applications and the apparent contribution of mobilised biomass to yield, it seems that the yield of oilseed rape was more source-limited during grain filling than that of wheat, particularly at the medium and high N levels. Both species recovered equal amounts of N from the total available N in the soil and had similar N use efficiencies, expressed as yield per unit of N absorbed. However, oilseed rape had higher efficiency to convert absorbed N in biomass, but lower harvest index of N than wheat. Oilseed rape had similar or lower root biomass than wheat, depending on N level, but higher root length per unit soil volume and specific root length. The specific uptake rate of N per unit root dry weight during the critical period for grain number determination was higher in oilseed rape than in wheat. In wheat, N limitation affected growth through a similar or lower reduction in radiation use efficiency corrected for synthesis costs (RUESC) than in the cumulative amount of intercepted photosynthetically active radiation (IPARc). In oilseed rape, lower growth due to N shortage was associated more with RUESC than IPARc, during flowering while during grain filling both components contributed similarly to decreased growth. RUESC and the concentration of N in leaves and inflorescence (LIN%) decreased from flowering to maturity and were curvilinearly related. Oilseed rape tended to have higher RUESC than wheat at high N supply during the critical period for grain number determination, and generally lower during grain filling. The reasons for these differences and possibilities to increase yield potential are discussed in terms of the photosynthetic efficiency of the different organs and changes in source–sink ratio during reproductive stages.

Contents, Uptake Rates and Reduction of Nitrate of Rumex palustris and Plantago major spp. major Grown on Compacted Soil

1. Net nitrate-uptake rates, nitrogen contents and nitrate-reduction rates of Rumex palustris and Plantago major spp. major plants grown on loose or compacted soil were studied. 2. Compaction lead to a slower growth rate for both species. Accumulation of nitrate caused increased internal nitrogen concentrations in P. major when grown on compacted soil. 3. After transfer to a nutrient solution plants of both species grown on compacted soil showed faster nitrate-uptake rates, when expressed per unit lateral-root length or lateral-root surface, than plants grown on loose soil. For Plantago, rates also increased when expressed per unit shoot or root dry weight. 4. Based on measured nitrate-reductase rates, only R. palustris should be able to reduce the largest part of the amount of nitrate taken up from the nitrate solution in the time period it was exposed to this solution. 5. Nitrate-reductase activities of R. palustris and the shoot of P. major correlated well with the internal nitrate concentrations. Roots of P. major showed no correlation at all. A possible explanation for this is compartment of nitrate and nitrate-reductase activities in these roots. 6. The accumulation of nitrate in roots of P. major, occurring on compacted soils, may be beneficial for maintaining the osmotic potential needed to penetrate soils with a high mechanical resistance. Rumex palustris, a species not occurring on compacted soils, does not show such an accumulation

Comparison of root growth and nitrogen absorbing ability between Gramineae and Leguminosae during the vegetative stage

Abstract Eight Gramineae crops (rice, spring wheat, barley, oat, maize, sorghum, redtop, and orchardgrass), and seven Leguminosae crops (soybean, field bean, adzuki bean, lupin, pea, alfalfa, and red clover) were grown in a field. The characteristics of nitrogen absorption were parametrized as root size (root length or dry weight), root activity (specific absorption rate of nitrogen per unit root dry weight; SARN), and photosynthetic factors (crop growth rate (CGR), leaf area index and net assimilation rate). The results were as follows. 1) The rate of nitrogen accumulation by plant (ΔN) was highly correlated with the crop growth rate (CGR), and dry matter accumulation per unit amount of nitrogen accumulated in plant was lower in Leguminosae than in Gramineae. 2) In Leguminosae, the length or weight of root (root size) was generally shorter or smaller than in Gramineae. However, SARN of Leguminosae was higher than that of Gramineae. Therefore, the increase in the root size was considered to contribute mor...

429 PB 168 NET AMMONIUM UPTAKE BY ROOTS OF FIELD-GROWN PEACH TREES IS INVERSELY RELATED TO TREE NITROGEN STATUS

The relationship between nitrogen (N) status and N uptake capacity has not been assessed in fruit trees. Determination of root uptake capacity by depletion of unlabeled N from external solution is less costly than methods using 15N, but is reportedly not suited for excised root studies due to reductions in uptake rates with time (Pearcy, R.W. et al. (eds). 1989. Plant Physiological Ecology, p. 195. Chapman and Hall. New York.). We tested two hypotheses: I) excised peach root NH4+ uptake rates are constant over several hours exposure to NH4+ solution and 2) excised peach root NH4+ uptake rates are negatively correlated with tree N status. Mature, N deficient, field grown `O'Henry' trees on `Lovell' peach (Prunus persica L. Batch.) rootstocks and growing in Winters, CA received (NH4)2SO4 at a rate of 200 kg N/ha on September 29, 1993. An equal number of control trees received no N fertilizer. Foliar N deficiency symptoms of fertilized trees disappeared within 3 weeks of fertilization. On Nov. 9, 1993 (prior to leaf fall), excised roots were obtained from two fertilized and two unfertilized trees. Root NH4+ accumulation rates per unit root dry weight or root length were constant over 5 hours of exposure to 70 μM NH4+ (initial concentration) for both fertilized and unfertilized trees. Unfertilized tree root NH4+ uptake rates were significantly greater than those of fertilized trees on a root dry weight or length basis. Excised root NH4+ uptake may prove to be a sensitive index of fruit tree N status.