P Supply (p + supply)

Distribution by Scientific Domains

Selected Abstracts

Molecular analysis of the phosphorus starvation response in Trichodesmium spp.

Elizabeth D. Orchard
Summary The marine diazotroph Trichodesmium is a major contributor to primary production and nitrogen fixation in the tropical and subtropical oceans. These regions are often characterized by low phosphorus (P) concentrations, and P starvation of Trichodesmium could limit growth, and potentially constrain nitrogen fixation. To better understand how this genus responds to P starvation we examined four genes involved in P acquisition: two copies of a high-affinity phosphate binding protein (pstS and sphX) and two putative alkaline phosphatases (phoA and phoX). Sequence analysis of these genes among cultured species of Trichodesmium (T. tenue, T. erythraeum, T. thiebautii and T. spiralis) showed that they all are present and conserved within the genus. In T. erythraeum IMS101, the expression of sphX, phoA and phoX were sensitive to P supply whereas pstS was not. The induction of alkaline phosphatase activity corresponded with phoA and phoX expression, but enzyme activity persisted after the expression of these genes returned to basal levels. Additionally, nifH (nitrogenase reductase; involved in nitrogen fixation) expression was downregulated under P starvation conditions. These data highlight molecular level responses to low P and lay a foundation for better understanding the dynamics of Trichodesmium P physiology in low-P environments. [source]

A global study of relationships between leaf traits, climate and soil measures of nutrient fertility

GLOBAL ECOLOGY, Issue 2 2009
Jenny C. Ordo˝ez
ABSTRACT Aim This first global quantification of the relationship between leaf traits and soil nutrient fertility reflects the trade-off between growth and nutrient conservation. The power of soils versus climate in predicting leaf trait values is assessed in bivariate and multivariate analyses and is compared with the distribution of growth forms (as a discrete classification of vegetation) across gradients of soil fertility and climate. Location All continents except for Antarctica. Methods Data on specific leaf area (SLA), leaf N concentration (LNC), leaf P concentration (LPC) and leaf N:P were collected for 474 species distributed across 99 sites (809 records), together with abiotic information from each study site. Individual and combined effects of soils and climate on leaf traits were quantified using maximum likelihood methods. Differences in occurrence of growth form across soil fertility and climate were determined by one-way ANOVA. Results There was a consistent increase in SLA, LNC and LPC with increasing soil fertility. SLA was related to proxies of N supply, LNC to both soil total N and P and LPC was only related to proxies of P supply. Soil nutrient measures explained more variance in leaf traits among sites than climate in bivariate analysis. Multivariate analysis showed that climate interacted with soil nutrients for SLA and area-based LNC. Mass-based LNC and LPC were determined mostly by soil fertility, but soil P was highly correlated to precipitation. Relationships of leaf traits to soil nutrients were stronger than those of growth form versus soil nutrients. In contrast, climate determined distribution of growth form more strongly than it did leaf traits. Main conclusions We provide the first global quantification of the trade-off between traits associated with growth and resource conservation ,strategies' in relation to soil fertility. Precipitation but not temperature affected this trade-off. Continuous leaf traits might be better predictors of plant responses to nutrient supply than growth form, but growth forms reflect important aspects of plant species distribution with climate. [source]

Genotypic variation of potato for phosphorus efficiency and quantification of phosphorus uptake with respect to root characteristics

Tesfaye Balemi
Abstract Potato (Solanum tuberosum L.), an important food crop, generally requires a high amount of phosphate fertilizer for optimum growth and yield. One option to reduce the need of fertilizer is the use of P-efficient genotypes. Two efficient and two inefficient genotypes were investigated for P-efficiency mechanisms. The contribution of root traits to P uptake was quantified using a mechanistic simulation model. For all genotypes, high P supply increased the relative growth rate of shoot, shoot P concentration, and P-uptake rate of roots but decreased root-to-shoot ratio, root-hair length, and P-utilization efficiency. Genotypes CGN 17903 and CIP 384321.3 were clearly superior to genotypes CGN 22367 and CGN 18233 in terms of shoot,dry matter yield and relative shoot-growth rate at low P supply, and therefore can be considered as P-efficient. Phosphorus efficiency of genotype CGN 17903 was related to higher P-utilization efficiency and that of CIP 384321.3 to both higher P-uptake efficiency in terms of root-to-shoot ratio and intermediate P-utilization efficiency. Phosphorus-efficient genotypes exhibited longer root hairs compared to inefficient genotypes at both P levels. However, this did not significantly affect the uptake rate and the extension of the depletion zone around roots. The P inefficiency of CGN 18233 was related to low P-utilization efficiency and that of CGN 22367 to a combination of low P uptake and intermediate P-utilization efficiency. Simulation of P uptake revealed that no other P-mobilization mechanism was involved since predicted uptake approximated observed uptake indicating that the processes involved in P transport and morphological root characterstics affecting P uptake are well described. [source]

Effects of phosphate supply and elevated CO2 on root acid phosphatase activity in Pinus densiflora seedlings

Mariko Norisada
Abstract The exudation of root acid phosphatase (APase) is a plant response mechanism to phosphorus (P) deficiency. Under conditions of elevated CO2, P demand increases and possibly further enhances APase activity. We examined the activity of APase in 1-year-old ectomycorrhizal Pinus densiflora Sieb. et Zucc. seedlings grown in potted sand in the greenhouse under ambient (400 ,mol mol,1) and elevated (700 ,mol mol,1) CO2 with three modes of P supply: inorganic (NaH2PO4; Pin), organic (inositol hexaphosphate dodecasodium salt; Porg), and no phosphate (P0) for 78 d. Phosphorus limitations decreased P content in leaves and roots with lowest P content in P0 treatments, irrespective of CO2 conditions. However, P limitations decreased plant biomass at elevated CO2 levels, but not at ambient CO2 levels. The content in leaves of nutrients other than P was mostly unaffected by P supply, but decreased under elevated CO2. This observation was attributed to starch accumulation in leaves at elevated CO2, especially in the P0 treatment. The photosynthetic activity (expressed per unit of chlorophyll) was unaffected by P supply, but tended to be less at elevated CO2. There was no increase in root APase activity of Pinus densifolia in response to the P shortage caused by elevated CO2. [source]

Citrate exudation from white lupin induced by phosphorus deficiency differs from that induced by aluminum

B. L. Wang
Summary ,,Both phosphorus (P) deficiency and aluminum (Al) toxicity induce root exudation of carboxylates, but the relationship between these two effects is not fully understood. Here, carboxylate exudation induced by Al in Lupinus albus (white lupin) was characterized and compared with that induced by P deficiency. ,,Aluminum treatments were applied to whole root systems or selected root zones of plants with limited (1 Ám) or sufficient (50 Ám) P supply. ,,Aluminum stimulated citrate efflux after 1,2 h; this response was not mimicked by a similar trivalent cation, La3+. P deficiency triggered citrate release from mature cluster roots, whereas Al stimulated citrate exudation from the 5- to 10-mm subapical root zones of lateral roots and from mature and senescent cluster roots. Al-induced citrate exudation was inhibited by P limitation at the seedling stage, but was stimulated at later growth stages. Citrate exudation was sensitive to anion-channel blockers. Al treatments did not affect primary root elongation, but inhibited the elongation of lateral roots. ,,The data demonstrate differential patterns of citrate exudation in L. albus, depending on root zone, developmental stage, P nutritional status and Al stress. These findings are discussed in terms of possible functions and underlying mechanisms. [source]

Phosphorus nutrition-mediated effects of arbuscular mycorrhiza on leaf morphology and carbon allocation in perennial ryegrass

AgustÝn A. Grimoldi
Summary ,,The aim of this work was to disentangle phosphorus status-dependent and -independent effects of arbuscular mycorrhizal fungus (AMF) on leaf morphology and carbon allocation in perennial ryegrass (Lolium perenne). ,,To this end, we assessed the P-response function of morphological components in mycorrhizal and nonmycorrhizal plants of similar size. ,,AMF (Glomus hoi) stimulated relative P-uptake rate, decreased leaf mass per area (LMA), and increased shoot mass ratio at low P supply. Lower LMA was caused by both decreased tissue density and thickness. Variation in tissue density was almost entirely caused by variations in soluble C, while that in thickness involved structural changes. ,,All effects of AMF were indistinguishable from those mediated by increases in relative P-uptake rate through higher P-supply rates. Thus the relationships between relative P-uptake rate, leaf morphology and C allocation were identical in mycorrhizal and nonmycorrhizal plants. No evidence was found for AMF effects not mediated by changes in plant P status. [source]

Phosphorus and the regulation of nodulation in the actinorhizal symbiosis between Discaria trinervis (Rhamnaceae) and Frankia BCU110501

Claudio Valverde
Summary ,,After nitrogen (N), phosphorus (P) is the nutrient that most limits plant productivity. The role of P on growth and root nodulation was studied in the actinorhizal symbiosis between Discaria trinervis and Frankia, an intercellular infected N2,fixing association. ,,Growth, nodulation and nutrient content (N and P) were analysed in symbiotic plants receiving different supplies of P in nutrient solutions. The relative requirement of P for nodulation was analysed in P-deficient plants. ,,Nodule initiation was less impaired than general plant growth by low P. However, low P impaired nodule growth to a greater extent than plant growth. The proportion of nodule biomass, although not the number of nodules per plant, was stimulated by P supply. Autoregulation of nodulation was not affected by P. Use of N was limited by availability of P. Reserves of P in seeds were enough for the seedling to establish nodules. However nodule (and plant) growth was limited in the absence of exogenous P. ,,It is possible that P interacts with the feedback control of nodule growth that is associated with the plant demand for N. Leaf N : P ratio is negatively correlated with the proportion of nodule tissue. [source]

Nitrogen and phosphorus availability limit N2 fixation in bean

Availability of nitrogen (N) and phosphorus (P) might significantly affect N2 fixation in legumes. The interaction of N and P was studied in common bean (Phaseolus vulgaris), considering their effects on nodulation and N2 fixation, nitrate reductase activity, and the composition of N compounds in xylem sap. The effect of N on the uptake of P by plants was estimated by analysing rhizospheric pH and P concentration in xylem sap and in plant shoots. Inoculated bean plants were grown in pots containing perlite/vermiculite in two experiments with different amounts of P and N. In a third experiment, bean plants were grown on two soil types or on river sand supplied with different concentrations of N. At harvest, shoot growth, number of nodules and mass, and nitrogenase activity were determined. Xylem sap was collected for the determination of ureides, amino acids, nitrate and phosphate concentration. At low nitrate concentration (1 mM), increasing amounts of P promoted both nodule formation and N2 fixation, measured as ureide content in the xylem sap. However, at high nitrate concentration (10 mM), nodulation and N2 fixation did not improve with increased P supply. Glutamine and aspartate were the main organic N compounds transported in the xylem sap of plants grown in low nitrate, whereas asparagine was the dominant N compound in xylem sap from plants grown in high nitrate. Nitrate reductase activity in roots was higher than in shoots of plants grown with low P and high N. In both soils and in the sand experiment, increased application of N decreased nodule mass and number, nitrogenase activity and xylem ureides but increased the concentration of asparagine in xylem sap. Increasing P nutrition improved symbiotic N2 fixation in bean only at low N concentrations. It did not alleviate the inhibitory effect of high nitrate concentration on N2 fixation. A decrease in plant P uptake was observed, as indicated by a lower concentration of P in the xylem sap and shoots, correlating with the amount of N supplied. Simultaneously with the specific inhibition of N2 fixation, high nitrate concentrations might decrease P availability, thus inhibiting even further the symbiotic association because of the high P requirement for nodulation and N2 fixation. [source]

Growth in epiphytic bromeliads: response to the relative supply of phosphorus and nitrogen

PLANT BIOLOGY, Issue 1 2010
G. Zotz
Abstract Insufficient nitrogen (N) and phosphorus (P) frequently limit primary production. Although most nutrient studies on vascular epiphytes have focused on N uptake, circumstantial evidence suggests that P rather than N is the most limiting element for growth in this plant group. We directly tested this by subjecting a total of 162 small individuals of three bromeliad species (Guzmania monostachia, Tillandsia elongata, Werauhia sanguinolenta) to three N and three P levels using a full-factorial experimental design, and determined relative growth rates (RGR) and nutrient acquisition over a period of 11 weeks. Both N and P supply had a significant effect on RGR, but only tissue P concentrations were correlated with growth. Uptake rates of N and P, in contrast, were not correlated with RGR. Increased nutrient supply led to an up to sevenfold increase in tissue P concentration compared to natural conditions, while concentrations of N hardly changed or even decreased. All treatment combinations, even at the lowest experimental P supply, led to decreased N:P ratios. We conclude that P is at least as limiting as N for vegetative function under natural conditions in these epiphytic bromeliads. This conclusion is in line with the general notion of the prevalence of P limitation for the functioning of terrestrial vegetation in the tropics. [source]

Interactions between the effects of atmospheric CO2 content and P nutrition on photosynthesis in white lupin (Lupinus albus L.)

ABSTRACT Phosphorus (P) is a major factor limiting the response of carbon acquisition of plants and ecosystems to increasing atmospheric CO2 content. An important consideration, however, is the effect of P deficiency at the low atmospheric CO2 content common in recent geological history, because plants adapted to these conditions may also be limited in their ability to respond to further increases in CO2 content. To ascertain the effects of low P on various components of photosynthesis, white lupin (Lupinus albus L.) was grown hydroponically at 200, 400 and 750 Ámol mol,1 CO2, under sufficient and deficient P supply (250 and 0.69 Ám P, respectively). Increasing growth CO2 content increased photosynthesis only under sufficient growth P. Ribulose 1,5-biphosphate carboxylase/oxygenase (Rubisco) content and activation state were not reduced to the same degree as the net CO2 assimilation rate (A), and the in vivo rate of electron transport was sufficient to support photosynthesis in all cases. The rate of triose phosphate use did not appear limiting either, because all the treatments continued to respond positively to a drop in oxygen levels. We conclude that, at ambient and elevated CO2 content, photosynthesis in low-P plants appears limited by the rate of ribulose biphosphate (RuBP) regeneration, probably through inhibition of the Calvin cycle. This failure of P-deficient plants to respond to rising CO2 content above 200 Ámol mol,1 indicates that P status already imposes a widespread restriction in plant responses to increases in CO2 content from the pre-industrial level to current values. [source]

Physiological changes in soybean (Glycine max) Wuyin9 in response to N and P nutrition

Summary Phosphorus deficiency is a very common problem in the acid soil of central China. Previous research has shown that starter N and N topdressing at the flowering stage (Rl) increased soybean (Glycine max) yield and N2 fixation (Gan et al, 1997, 2000). However, there is little information available concerning soybean response to P-fertiliser in soybean production in central China (Gan, 1999). A field experiment was conducted to investigate the response to P (0 kg P ha,1, 22 kg P ha,1, 44 kg P ha,1 before sowing) and N fertiliser application (N1: 0 kg N ha,1, N2: 25 kg N ha,1 before sowing, N3: N2 + 50 kg N ha,1 at the V2 stage and N4: N2 + 50 kg N ha,1 at the R1 stage) on growth, yield and N2 fixation of soybean. Both N and P fertiliser increased growth and seed yield of soybean (P < 0.01). Application of basal P fertiliser at 22 kg P ha,1 or 44 kg P ha,1 increased total N accumulation by 11% and 10% (P < 0.01) and seed yield by 12% and 13% (P < 0.01), respectively, compared to the zero P treatment. Although application of starter N at 25 kg N ha,1 had no positive effect on seed yield at any P level (P > 0.05), an application of a topdressing of 50 kg N ha,1 at the V2 or R1 stage increased total N accumulation by 11% and 14% (P < 0.01) and seed yield by 16% and 21% (P < 0.01), respectively, compared to the zero N treatment. Soybean plants were grown on sterilised Perlite in the greenhouse experiment to study the physiological response to different concentrations of phosphate (P1: 0 mM; P2: 0.05 mM; P3: 0.5 mM; P4:1.0 mN) and nitrate (N1: 0 mM with inoculation, N2: 20 mM with inoculation). The result confirmed that N and P nutrients both had positive effects on growth, nodulation and yield (P < 0.01). The relative importance of growth parameters that contributed to the larger biomass with N and P fertilisation was in decreasing order: (i) total leaf area, (ii) individual leaf area, (iii) shoot/root ratio, (iv) leaf area ratio and (v) specific leaf area. The yield increase at N and P supply was mainly associated with more seeds and a larger pod number per plant, which confirmed the result from the field experiment. [source]

Pyruvate protection against ,-amyloid-induced neuronal death: Role of mitochondrial redox state

Gema Alvarez
Abstract The mechanism by which ,-amyloid protein (A,) causes degeneration in cultured neurons is not completely understood, but several lines of evidence suggest that A,-mediated neuronal death is associated with an enhanced production of reactive oxygen species (ROS) and oxidative damage. In the present study, we address whether supplementation of glucose-containing culture media with energy substrates, pyruvate plus malate (P/M), protects rat primary neurons from A,-induced degeneration and death. We found that P/M addition attenuated cell death evoked by ,-amyloid peptides (A,25,35 and A,1,40) after 24 hr treatment and that this effect was blocked by ,-ciano-3-hydroxycinnamate (CIN), suggesting that it requires mitochondrial pyruvate uptake. P/M supply to control and A,-treated neuronal cultures increases cellular reducing power, as indicated by the ability to reduce the dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The early increases in ROS levels, measured by dichlorofluorescein (DCF) fluorescence, and caspase-3 activity that follow exposure to A, were notably reduced in the presence of P/M. These results place activation of caspase-3 most likely downstream of oxidative damage to the mitochondria and indicate that mitochondrial NAD(P) redox status plays a central role in the neuroprotective effect of pyruvate. Inhibition of respiratory chain complexes and mitochondrial uncoupling did not block the early increase in ROS levels, suggesting that A, could initiate oxidative stress by activating a source of ROS that is not accesible to the antioxidant defenses fueled by mitochondrial substrates. ę 2003 Wiley-Liss, Inc. [source]