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Background and aims: Plant and soil microbes can reduce their phosphorus (P)-requirements by replacing phospholipids with non-P containing lipids (e.g., galactolipids, sulfolipids, and betaine lipids). There have been few studies of this process in the field (i.e., in natural ecosystems); thus, it is unclear whether a similar replacement of phospholipids with non-P lipids occurs across natural gradients of soil P-availability. Methods: We compared the membrane lipid profiles of plant leaves, roots, and soil microbial communities between two adjacent native Australian sclerophyll forest ecosystems—one situated on a severely P-deficient sandstone-derived soil and the other on a comparatively P-rich shale-derived soil. The herbaceous species, Lomandra longifolia, which occurred across both soils was sampled, along with two Myrtaceae tree species associated with each soil type. Results: The phospholipid content of plant leaves and soil microbes was two- to three-fold greater in the shale site than the sandstone site, but non-P lipid content did not differ between sites. Conclusion: Our results indicate that plants and soil microbes can have a lower investment of P into phospholipids in response to P-deficiency without a concomitant increase in non-P lipid content. Modulations in phospholipid concentration occurred across all plant- and soil microbial-associated phospholipid classes. [ABSTRACT FROM AUTHOR]

Background and aims: The addition of functional soil microbes to the soil can enhance the utilization of soil phosphorus (P) for plants, but the mechanisms underlying this process are not fully understood. The study aimed to investigate the effects of inoculating phosphate-solubilizing microorganisms (PSMs), with or without arbuscular mycorrhizal fungi (AMF), on Phyllostachys edulis seedling growth in soils with varying P levels. Methods: The pot experiment was conducted on P. edulis seedings with inoculation treatments of a mixture of 15 PSMs from the P. edulis rhizosphere alone, or PSMs in cooperation with AMF. Plant mass and nutrient concentrations, soil properties and soil microbial communities were assessed when the seedlings had completed their first-year growth spurt (T1) and second-year growth spurt (T2). Results: The application of PSMs, particularly in combination with AMF, resulted in significant increases in seedling mass and nutrient content under P-deficient conditions, accomplished through modifications in soil nutrient concentrations and enzyme activities related to nitrogen, carbon, and P metabolism. The beneficial outcomes were accompanied by alterations in the composition and interactions within the constituents of the rhizosphere microbial community. Remarkably, the co-inoculation of AMF and PSMs led to a higher abundance of microorganisms that promote plant growth within the rhizosphere. Conclusion: The utilization of PSMs, especially in combination with AMF, proves to be an effective strategy for enhancing P. edulis seedlings growth during their second-year growth, particularly in P-deficient soil. This approach modifies the soil microenvironment, offering a promising avenue for improving soil P utilization by woody plants. [ABSTRACT FROM AUTHOR]

Background and Aims: The leaf economic spectrum (LES) is related to dry mass and nutrient investments towards photosynthetic processes and leaf structures, and to the duration of returns on those investments (leaf lifespan, LL). Phosphorus (P) is a key limiting nutrient for plant growth, yet it is unclear how the allocation of leaf P among different functions is coordinated with the LES. We addressed this question among 12 evergreen woody species co-occurring on P-impoverished soils in south-eastern Australia. Methods: Leaf 'economic' traits, including LL, leaf mass per area (LMA), light-saturated net photosynthetic rate per mass (Amass), dark respiration rate, P concentration ([Ptotal]), nitrogen concentration, and P resorption, were measured for three pioneer and nine non-pioneer species. Leaf P was separated into five functional fractions: orthophosphate P (Pi), metabolite P (PM), nucleic acid P (PN), lipid P (PL), and residual P (PR; phosphorylated proteins and unidentified compounds that contain P). Results: LL was negatively correlated with Amass and positively correlated with LMA, representing the LES. Pioneers occurred towards the short-LL end of the spectrum and exhibited higher [Ptotal] than non-pioneer species, primarily associated with higher concentrations of Pi, PN and PL. There were no significant correlations between leaf P fractions and LL or LMA, while Amass was positively correlated with the concentration of PR. Conclusions: Allocation of leaf P to different fractions varied substantially among species. This variation was partially associated with the LES, which may provide a mechanism underlying co-occurrence of species with different ecological strategies under P limitation. [ABSTRACT FROM AUTHOR]

Aims: Rainfed rice in subSaharan Africa suffers from combined drought and phosphorus (P) deficiency stresses. Enhanced root development under water stress may counteract the physical effects of drought lowering soil P bioavailability. This study was set up to evaluate how rice genotypes respond differently to variable water stress in P deficient conditions. Methods: A greenhouse study was conducted with a full factorial combination of six genotypes, two soil P treatments (strong to moderate P deficiency) and two irrigation (W) regimes (rainfed limited and adequate). Plants were grown for 49 days and root traits were measured. Results: The overall effects of P supply on shoot weight were larger than overall effects of water supply, water stress effects were most pronounced at highest P supply because of the higher transpiration in larger plants. Reduced water supply did not enhance P stress, and the stress antagonisms were genotype dependent. There was no genotypic variation in the increased root development in response to drought that would lead to increased P uptake. Root weight and root efficiency mainly explained shoot P content across all water treatments and genotypes with marginal effects of root architectural traits. Conclusion: This study illustrates the importance of root biomass production and root efficiency under the combined stresses of water and P and corroborated the superior performance of genotypes Chhomrong Dhan and FOFIFA 172 that was found in the field. [ABSTRACT FROM AUTHOR]

Aims: Root exudation of organic acids is one of strategies for tropical trees to facilitate nutrient uptake from the highly weathered soils. However, paradoxical relationship remains that root exudation also stimulates microbial activities to consume organic acids in the rhizosphere (root-soil interface). Plant-specific root exudation might shape different rhizosphere carbon (C) cycles in soils under different tree species. We test whether root exudation and rhizosphere C fluxes of organic acids and sugars differ between soils under dominant dipterocarp trees (Dipterocapus cornutus and Shorea laevis) and pioneer trees (Macaranga spp.). Methods: We measured (1) root exudation from mature trees, (2) soil solution concentrations of organic acids and monosaccharides, and (3) mineralization kinetics of 14C-radiolabelled substrates in the rhizosphere and bulk soils of the Dipterocarp and Macaranga trees. Results: Malate was a dominant organic acid exuded from Dipterocarp roots, while monosaccharides were dominant exudates of pioneer Macaranga trees. Malate exudation rates by Dipterocarp roots were greater compared to Macaranga roots. Organic acid exudation increased with increasing root surface area and with decreasing soil pH. Microbial activities of malate mineralization were enhanced in the rhizosphere both under Dipterocarp and Macaranga trees, but the C fluxes of malate mineralization far exceeded root exudation of malate in the rhizosphere of Dipterocarp trees. Conclusion: Tree species develop different strategies to increase malate concentration in rhizosphere soil directly through root exudation or indirectly through rhizosphere microbial activities to increase malate production, which might be favorable for phosphorus solubilization, aluminum detoxification, and lignin degradation in acidic soils. [ABSTRACT FROM AUTHOR]

Aims: Phosphorus (P) mobility depends on the availability of water in soil, both of which are limited resources for crop production. We studied the mechanisms governing tolerance to P-deficiency and drought stress in contrasting mungbean accessions. Methods: Tolerant (IC333090 and IC507340) and sensitive (IC488526 and EC397142) mungbean accessions were grown in soil under four treatments: control (sufficient P, irrigated), P-deficiency (no P, irrigated), drought (sufficient P, irrigation withheld), combined stress (no P, irrigation withheld), followed by a 48 h recovery. Results: Drought stress reduced the relative water content and membrane stability index, affecting overall plant growth. The tolerant accessions maintained significantly higher root growth, leaf area, and biomass under combined stress (P-deficiency and drought) than the sensitive accessions, mainly due to enhanced nutrient uptake and symbiotic N2-fixation. The combined stress also increased osmolyte concentration, antioxidative compounds, and the scavenging activity of antioxidant enzymes in tolerant accessions. Recovery from drought stress significantly reduced osmolyte concentration. Transcript abundance of candidate genes related to P-deficiency and drought under individual and combined stress, was significantly higher in leaves of IC333090 than IC488526. IC333090 recovered from drought stress better than IC488526 due to the enhanced expression of stress-responsive genes. Conclusions: Physiological traits, such as the accumulation of total soluble sugars and reduced glutathione, ascorbate, and scavenging activity of antioxidant enzymes, facilitated by the differential expression of stress-responsive genes impart cross-tolerance to P-deficiency and drought stress in tolerant mungbean accessions. Hence, accession IC333090 is potential genetic stock for tolerance to drought, P-deficiency, and combined stresses. [ABSTRACT FROM AUTHOR]

Background and aims: Soil phosphorus (P) availability, as well as shoot P status, may alter root morphology. However, how root morphological traits to light intensity under various P environments remains unknown. Methods: Maize (Zea mays L.) cultivar CD418 grew under nine P application rates (ranged from 0 to 300 mg P kg−1 soil, supplied as KH2PO4) under natural light intensity (NL) and low light intensity (LL, 40% of natural light intensity) in a naturally-lit rain-shed. Plant growth, P uptake, and responses of root morphological traits (i.e. total root length, root surface area, and proportion of <0.2 mm diameter fine root) in the light and P treatments were assessed after 36 d of growth (five-leaf stage). Results: Shoot and root dry weights increased under the natural light intensity in all P treatments. The ratio of root to shoot dry weight increased under NL when the soil Olsen-P was below 15.9 mg kg−1. At relatively low soil P availability (6.7 to 15.9 mg kg−1), total root length, root surface area, and fine root percentage were enhanced with increases in light intensity from LL to NL. These effects diminished in soil with either severely low P (2.6 mg kg−1) or excess P (above 20.6 mg kg−1). Express of the low P-tolerance transcription factor ZmPTF1 (that influences root growth by regulating carbon metabolism in leaves and roots), P uptake, and fertilizer P use efficiency were higher under NL than LL, especially under low P conditions (Olsen-P 6.7–15.9 mg kg−1). Increased responses of root morphological traits to low P conditions were associated with relatively low P concentrations in the leaves and high sucrose concentrations in the roots. Conclusions: Compared to LL, under P deficiency and NL conditions, maize allocated more photosynthates to roots as sucrose, which acts as a low-P signal; in addition, sucrose as a carbon and energy source stimulated root growth and, consequently, adaptation of maize to low P stress. [ABSTRACT FROM AUTHOR]

Aims: High pH, and high bicarbonate (HCO3−) and calcium (Ca) availability characterise calcareous soils. High [Ca] only partially explains why some Lupinus species are calcifuge, so we explored high [HCO3−] and high pH. Methods: We grew six Lupinus genotypes in hydroponics with pH 5, 6.5 and 8a (adjusted by KOH), and 8b (adjusted by KHCO3). Leaf symptoms and areas, root appearance and biomass were recorded; whole leaf and root nutrient concentrations, and leaf cellular phosphorus (P), Ca and potassium (K) concentrations were determined using elemental X-ray microanalysis. Results: Chlorosis was observed in young leaves at high pH for L. angustifolius and L. cosentinii, and P deficiency at high pH for all genotypes. High pH decreased iron (Fe) and zinc (Zn) uptake in all genotypes. It also decreased lateral root growth, the uptake of P, K, Ca, and manganese (Mn) by all sensitive species; and translocation of P, Fe, Zn, Mn, and Ca to leaves in most sensitive species. However, leaf [Ca], leaf [K], [K] within each measured cell type, and translocation of K and Ca to leaves of L. pilosus and L. cosentinii at pH 8 were greater than at pH 5 and 6.5. Compared with pH 8a, all L. angustifolius genotypes translocated more P, Fe, Zn, Mn and K from roots to leaves at pH 8b. High pH did not affect the leaf cell types that accumulated P and Ca, but decreased the leaf cellular [P]. Conclusions: Lupinus angustifolius and L. cosentinii were sensitive to high [HCO3−] and/or high pH; L. pilosus was relatively tolerant. High pH decreased lateral root growth and nutrient uptake, inhibiting growth of sensitive species. High [HCO3−] diminished the negative effect of pH 8 on nutrient translocation to leaves in most L. angustifolius genotypes. This knowledge provides critical insights into the habits of Lupinus species to guide breeding of calcicole plants. [ABSTRACT FROM AUTHOR]

Background and aim: Phosphorus (P) is an essential macronutrient with major impacts on global crop productivity. Recent work showed that chlorophyll a fluorescence analysis can be used as a sensitive indicator of latent P deficiency across different plant species. Here, we demonstrate that chlorophyll a fluorescence OJIP transients are a powerful tool for early detection of P deficiency directly in the field.Methods: Barley was grown in a P responsive field. One treatment received 30 kg P ha−1 at sowing, four treatments were fertilized with P at 26, 35, 46 or 56 days after sowing (DAS), respectively, and the final treatment did not receive any P throughout the experiment. Chlorophyll a fluorescence measurements, multi-elemental leaf analysis, and growth stage evaluation were performed 26, 35, 46, 56, and 69 DAS.Results: Phosphorus deficiency during early vegetative growth irreversibly affected plant development including tiller outgrowth and grain yields. However, in the present study, yield reduction could be avoided if short-term P deficiency was corrected by application of P fertilizer no later than 35 days after sowing, when plants had not yet entered the tillering stage. The chlorophyll a fluorescence OJIP transients were able to detect latent P deficiency in this critical phase, thereby providing an opportunity for avoiding a potential yield reduction of up to 27 hkg ha−1. It was further noted, that chlorophyll a fluorescence analysis and P leaf tissue analysis should be performed during early vegetative growth, as probable remobilization of P within the plant during tillering and shoot differentiation masks the effects of P deficiency at the single leaf level.Conclusions: It is concluded that chlorophyll a fluorescence analysis provides a unique opportunity for a timely detection and correction of P deficiency under field conditions to prevent yield reductions. [ABSTRACT FROM AUTHOR]

Background and Aims: Gluconacetobacter diazotrophicus (family Acetobacteraceae), is a N-fixing bacterium with capability of mineral solubilization through organic acid production. The aim of this work was to evaluate its capacity as a phosphate solubilizing bacterium to overcome a phosphorus deficiency in phosphorus-starved strawberry plants. Methods: Strawberry plants growing with available and not available phosphorus were inoculated with the wild type G. diazotrophicus PAL5 Pi-solubilizing strain and a Tn5-derivative mutant defective in organic acid production. Growth index, root acidification, root area, MPN, greenness index, and phosphorus content were evaluated. Results: Results demonstrate that G. diazotrophicus PAL5 can increase the phosphorus content of strawberry plants (root and shoot), and revert phosphorus deficiency. Additionally, bacterial plant growth-promoting effect was represented by higher values of biomass production, root area, and growth index, as compared with the controls. Conclusions: G. diazotrophicus can increase the phosphorus content of strawberry plants, promoting the overall plant growth. [ABSTRACT FROM AUTHOR]

Background and aims: Alterations in root growth and rhizosphere processes in maize ( Zea mays L.) occur under phosphorus (P) deficiency, but the dynamics of root morphological and physiological modifications with increasing shoot P concentration remain unclear. This study investigated root responses to a wide gradient in shoot P status. Methods: A range of maize shoot P concentrations (1.0-4.0 mg g) was established using controlled pot experiment with eleven rates of P supply from 0 to 1200 mg P kg soil. Root morphology and rhizosphere processes were characterized 28 days after planting. Results: Maize reached maximum biomass at shoot P concentration of 2.7 mg g. Root morphological responses (i.e. total root length, specific root length and proportion of fine roots) showed a strong increasing trend with decreasing shoot P concentration (1.1-1.3 mg g), but they decreased when shoot P concentration was extremely low (below 1.1 mg g). In contrast, with increasing shoot P concentration, root morphological responses decreased, but root physiological responses (rhizosphere acidification, acid phosphatase activity and carboxylate exudation in the rhizosphere) were enhanced, and no decrease was noted even at high shoot P concentration (4.0 mg g) corresponding to excess P supply. Conclusions: Increasing maize shoot P concentration induced a decrease in root morphological responses and an enhancement in root exudation, with maize response to P deficiency being dependent on root morphological rather than physiological traits. [ABSTRACT FROM AUTHOR]

Background and aims: This work aimed to quantify the critical external requirement for phosphorus (P) (i.e. extractable-P concentration required for 90 % of maximum yield) for a number of temperate legume species and understand differences in dry matter allocation, P distribution and P acquisition efficiency among these species. Methods: Shoot and root growth of five legume and one grass species was assessed in response to six rates of P mixed into the top 45 mm of soil in a pot experiment. Dactylis glomerata and Trifolium subterraneum were used as benchmark species; they are commonly grown together in mixed temperate pastures and have low and high critical external requirements for P, respectively. Growth was compared with four alternative legume species: Ornithopus compressus, Ornithopus sativus, Biserrula pelecinus and Trifolium hirtum, that have root morphologies better suited to soil exploration and nutrient acquisition than that of Trifolium subterraneum. Results: Dactylis glomerata, Ornithopus compressus and Ornithopus sativus had maximum yields equal to or greater than Trifolium subterraneum but achieved this at rates of P less than half that of Trifolium subterraneum. Biserrula pelecinus and Trifolium hirtum had critical P requirements between that of Trifolium subterraneum and the Ornithopus species, but also had lower yields. Root dry matter of Dactylis glomerata and the Ornithopus species in the fertilised soil layer was only marginally changed in response to low P supply. In contrast, Trifolium subterraneum, Trifolium hirtum and to a lesser extent Biserrula pelecinus markedly increased root dry matter allocation to this soil layer. Species with lower critical P requirements were able to take up more P per unit root dry mass than those with higher critical P requirements, particularly at lower levels of P addition. Conclusions: The high P acquisition efficiencies of the Ornithopus species and Dactylis glomerata were likely to have contributed to their low critical external P requirements. It was surmised that differences in root morphology traits underpin the differences in acclimation to low P stress and P acquisition efficiency among the species. [ABSTRACT FROM AUTHOR]

Aims: Soybean is a relatively large-seeded species and variation in seed size can affect plant establishment especially under phosphorus-deficient conditions. We evaluated to what extent differences in seed weight and seed phosphorus (P) content among genotypes and within genotypes affect plant growth at low and high P supply. Methods: Seedling growth of 42 soybean genotypes was evaluated in a pot trial. In addition, plant growth of selected genotypes was evaluated at different growth stages in two pot trials using various seed lots differing in seed weight per genotype. Results: Correlations between seed weight and plant biomass, shoot P content and root length among 42 genotypes were stronger at low than at high P supply. Within-genotype variation in seed weight affected shoot and root growth at different plant growth stages. At low P supply, plant growth was correlated with seed weight up to the flowering stage. Conclusions: It is concluded that seed weight largely affects growth especially at low P supply. Confounding effects due to variation in seed weight must be taken into account when screening soybean genotypes for low P tolerance. [ABSTRACT FROM AUTHOR]

Background and aims: Recent research has demonstrated the high accuracy of a new method for assessment of plant available P in soil called diffusive gradients in thin-films (DGT). The process of P released by additions of bicarbonate to soil samples simulating common soil P tests is yet to be assessed by the new method (DGT). The aim of this study was to identify the pools of soil P extracted by soil test methods (DGT, Colwell and resin) by comparing, in 32P–labelled soils, the specific activity (SA) of phosphorus extracted by common soil test extracts with the SA of wheat plants grown in a range of agricultural soils from southern Australia. Methods: Wheat (cv. Frame) was grown for 4 weeks in 14 soils that were labelled uniformly with carrier-free 32P. The specific activity (SA) of P (MBq 32P kg 31P −1) in each soil test extract was compared to the SA of P in the wheat plants. Results: The SA of P in plants were similar to P extracted by the Colwell extractant in only 4 of the 14 soils; while SA in plants and extractants corresponded in 10 of the soils for the resin method and in 12 of the soils for the DGT method. Phosphorus in the Colwell and resin extract solutions had significantly lower SAs compared to P in the plants for 10 and 4 of the soils, respectively, indicating greater extraction of non-labile P sources (unlabelled 31P). Phosphorus in the DGT extractant had significantly lower SA than the plants for 1 soil and in 1 soil the SA was higher. Overall, across all soils, 25 % of P extracted by the Colwell method was non labile compared to 9 % and 2 % for the resin and DGT methods, respectively. Conclusion: The new DGT method for extraction of soil P has the potential to accurately predict occurrences of P deficiency because it generally extracts the same pool of labile soil P accessed by wheat plants, while methods using bicarbonate solution (e.g. Colwell, Olsen) or water (resin) at wide soil:solution ratios are more likely to measure more non-labile forms of P in soil. [ABSTRACT FROM AUTHOR]

Aims and background: The DGT test is an emerging soil test to measure available phosphorus (P) in soils. Data from previous pot and field trials suggested a superior predictive power of this test relative to established soil P tests. Modeling also predicted that the critical DGT value (to obtain 80 % of the maximum yield) is plant specific. This study was set-up to test the DGT relative to established soil P tests in predicting the growth response to P addition across different tropical soils marked by P deficiency, for two plants with contrasting P demand. Methods: Maize ( Zea mays L.) and upland rice ( Oryza sativa L.) were grown in a greenhouse on 9 contrasting soils that were amended with P at increasing doses. Soil tests were measured on incubated soils for all P treatments. Results: Shoot dry weight increased with increasing P application by factors 2 to 90. The P doses required to reach 80 % of maximum dry weight or yield ranged from 20 to 580 mg P kg and were always larger for the faster growing maize than for rice. The DGT method and CaCl extractions explained relative yield of maize among soils better (R² = 0.84 and 0.69 respectively) than P determined by Olsen, Colwell, Bray-1, Mehlich-3, ammonium oxalate and resin extractions (R² < 0.53). In strong contrast, relative yields of rice were best predicted by Mehlich-3, Bray-1, Olsen and resin P (R² ~ 0.7) compared to DGT (R² = 0.59) and CaCl (R² = 0.12). The DGT P concentration in a soil to obtain 80 % of maximum growth, i.e. the critical DGT values, were 73 μg P L (maize) and 7 μg P L (rice). The critical DGT value measured for maize is in correspondence with literature. Conclusions: For tropical P deficient soils, intensity based indices of soil P availability such as DGT and CaCl, are superior to quantity based indices (i.e. the established soil P tests based on extraction) for maize with high P demand. However, the reverse is true for rice suggesting that diffusion of P in the soil as measured by DGT is not the main factor explaining P uptake for rice. [ABSTRACT FROM AUTHOR]

Background and aims: A soil test that samples nutrients only from fractions that are accessible to plants will predict availability and uptake more robustly than empirical tests. This can be tested by comparison of the isotope ratios (specific activity, SA) of the nutrient between plant and the soil extract. This study was set up to assess this requirement for the diffusive gradients in thin films technique (DGT), recently proposed as a soil P test, in comparison with conventional soil P tests viz. Olsen, Colwell, Bray-1, Mehlich-3, ammonium oxalate, anion exchange membranes (AEM) and 0.01 M CaCl solution. Methods: Maize ( Zea mays L.) was grown in two P-deficient soils from western Kenya with contrasting P sorption characteristics, amended with a low and a high P rate and labelled with P. Results: The SA in the plant shoot corresponded with that of the extracts of the different soil tests, except for CaCl and ammonium oxalate extracts, at the low P rate in the soil with low P sorption capacity, Teso soil. For the high P rate on this soil, differences in SA between maize shoot and soil test were small for all established soil tests, but significant for the Colwell, Bray-1, Mehlich-3 and AEM tests. The SA in the soil extracts was significantly smaller than that in the maize shoot for Sega the strongly P-sorbing soil at both P rates for all conventional tests, including AEM. This indicates that these tests extracted P from a pool that is not accessible to the plant. For the DGT test, however, there was no difference in SA between the maize shoot and the soil test, for any of the treatments. Conclusions: Most conventional soil tests can extract a fraction of P which is not available to maize. The DGT technique, however, only samples P from the plant-accessible pool. [ABSTRACT FROM AUTHOR]

nthropogenic contamination with Cu is an important issue and it is necessary to understand how Cu toxicity influences the uptake/acquisition of nutrients by plants. An experiment was conducted with soil-grown cowpea ( Vigna unguiculata (L.) Walp.) to investigate the interaction between Cu toxicity and P deficiency. Plant performance was related to the activity of Cu at the outer surface of the root plasma membrane, {Cu}, which was calculated from properties of the soil solution. The addition of Cu to the soil was found to reduce growth of plant shoots by inducing Cu toxicity, which was associated with a reduction in the shoot tissue Fe concentration. The critical value (50% reduction in shoot growth) determined for {Cu} in this soil-based experiment (3.8 μM) corresponds well to values determined previously. Importantly, regression analyses indicated that although the alleviation of P deficiency improved overall growth, the P-status of the plant did not influence the apparent toxicity of the Cu. This result was unexpected, given that Cu inhibits the growth of roots hairs; these being important for the uptake of immobile nutrients such as P. This study advances our understanding of Cu toxicity and its impact upon nutrient uptake. [ABSTRACT FROM AUTHOR]

Failures of tailings dams have degraded large areas of agricultural alluvial soils worldwide, and concomitant soil pollution studies are abundant. Yet, the data on the actual effects of thereby imposed stresses on major crops are scarce. This work analyses the effect of pyrite tailings from a copper mine, deposited over crop fields by long-term flooding, on wheat ( Triticum aestivum L.) under field conditions. The major previously reported polluting agents were Cu, As, Zn, Pb and acidity generated by sulphide oxidation. Flexible systematic sampling, based on visual symptoms in wheat, included transects through partially damaged fields (from calcareous to acid soils). Multivariate analysis of soil properties, leaf mineral composition and growth parameters revealed a consistent underlying soil gradient of decreasing available P and increasing S. Phosphorus was shown to have the highest unique contribution to predicting wheat yield, consistent correlation with growth and visual symptoms, and concentrations in the range of severe deficiency. In P deficient plants N deficiency, decrease of available micronutrients and increase of As occur irrespectively of their soil concentrations, and the competition with superior 'pyrite' weeds increases. Different sorption of P and possible rhizotoxic effects of other pollutants imply that fertilization can hardly be a solution. [ABSTRACT FROM AUTHOR]

We used data from 33 field experiments with 4 year old Pinus radiata in which response to phosphate fertilisers was measured. We divided the data into two categories: one in which there was cultivation and weed control, and one in which there was neither because interactions between effects of fertilisation and those of weed control are common. We used the ratio of stem volume index between unfertilized and fertilized trees as a measure of the response. We measured Bray P as an indicator of inorganic phosphorus (P) availability in the soils, and continued the extraction for a total of ten times in order to reflect the ability of the soil to continue to supply P. Responses of trees to phosphate fertilisation were related to Bray P by a Mitscherlich equation. The equation differed between the two categories. The soils differed in the extent to which they were able to maintain supply to the repeated extractions. With some soils, the amounts extracted declined rapidly with successive extractions; with others they declined less rapidly and in some soils the second extraction removed more phosphate than the first extraction. The cumulated amount of extracted P (y) was described as a function of the number of extractions (N) using the equation, y = αN where b = βN . In this equation, the β parameter was a measure of the ability of the soils to maintain phosphorus supply under repeated extraction. When this parameter was added to a modified Mitscherlich equation, r-squared increased from 0.495 to 0.644 for the data in which there was weed control or soil cultivation. Response to fertilisation was significantly ( P = 0.001) better predicted by the repeated Bray P extraction modelling procedure than it was by a single Bray P extraction for each soil among data from plots with either weed control or cultivation. In soils that lacked both weed control and cultivation interactions between effects of weed competition and fertilisation very likely contributed to the lack of any clear relationships between repeated Bray P extractions and response to fertilisation. Further validation of the results reported here may lead to better predictions of effects of fertilisation on crop growth from soil samples. [ABSTRACT FROM AUTHOR]

The ability of the Diffusive Gradients in Thin Films (DGT) technique and two other established testing methods (Colwell, resin) to predict wheat responsiveness to applied P from 35 field trials across southern Australia was investigated. Regression analysis of relative early dry matter production and grain yield responses demonstrated that the DGT method predicted plant responsiveness to applied P more accurately than Colwell P and resin P at sites where maximum yields were reached with P rates used (20 out of 35). The measured concentration in soils at the DGT surface, C, explained 74% of the variation in response for both early dry matter and grain, compared to 7% for early dry matter and 35% for grain using the resin P method. No significant relationships could be obtained for Colwell P although modifying the Colwell test data using Phosphorus Buffering Index resulted in a correct response prediction for 11 of the 20 field sites compared to 18 for DGT and 14 for resin P. These observations suggest that the DGT technique can assess plant available P in soils with significantly greater accuracy than traditional soil P testing methods. The critical P threshold, expressed as C, was 255 μg L for early dry matter and 66 μg L for grain. [ABSTRACT FROM AUTHOR]

Proteoid roots are a unique adaptation that allow white lupin ( Lupinus albus L. var Ultra) to survive under extreme phosphorus (P) deficient conditions. The cascade of events that signals P-deficiency induced gene expression in proteoid roots remains unknown. Through promoter::GUS analysis we showed that expression of acid phosphatase ( LaSAP1) in P-deficient proteoid roots depends on DNA located from −465 bp to −345 bp 5′ of the ATG start codon and that the P1BS (PHR1 Binding Site) element, located at −160 bp, also contributes regulatory control. DNA located within the −414 bp to −250 bp region of the LaSAP1 promoter was bound by nuclear proteins isolated from P-sufficient normal roots in electrophoretic mobility shift assays (EMSA), suggesting negative regulation. Competition experiments were performed with unlabeled oligonucleotides to further delineate the region of the LaSAP1 promoter bound by P-sufficient normal root nuclear proteins to a motif spanning −361 bp to −346 bp. The promoter motif characterized through EMSA spanning −361 bp to −345 bp was used as “bait” in a yeast one-hybrid (Y1H) experiment and 31 putative DNA binding proteins were isolated. Taken together, our results increase understanding of P-deficiency signaling by identifying regulatory regions and putative regulatory proteins for LaSAP1 expression. [ABSTRACT FROM AUTHOR]

The study examined the interactive effect of pH and P supply on cluster-root formation, carboxylate exudation and proton release by an alkaline-tolerant lupin species ( Lupinus pilosus Murr.) in nutrient solution. The plants were exposed to 1 (P1, deficient) and 50 µM P (P50, adequate) for 34 days in nutrient solution at either pH 5.6 or 7.8. Plant biomass was not influenced by pH at P1, but at P50 shoot and root dry weights were 23 and 18% higher, respectively, at pH 7.8 than at pH 5.6. There was no significant difference in plant biomass between two P treatments regardless of medium pH. Phosphorus deficiency increased significantly the number of the second-order lateral roots compared with the P50 treatment. Both total root length and specific root length of plants grown at pH 5.6 were higher than those at pH 7.8 regardless of P supply. Cluster roots were formed at P1, but cluster-root number was 2-fold higher at pH 7.8 than pH 5.6. Roots released 16 and 31% more protons at pH 5.6 and 7.8, respectively, in P1 than in P50 treatments, and the rate of proton release followed the similar pattern. At pH 5.6, citrate exudation rate was 0.39 µmol g−1 root DW h−1 at P1, but was under the detection limit at P50; at pH 7.8, it was 2.4-fold higher in P1 than in P50 plants. High pH significantly increased citrate exudation rate in comparison to pH 5.6. The uptake of anions P and S was inhibited at P1 and high pH increased cations Na, Mg and Ca uptake. The results suggested that enhanced cluster-root formation, proton release and citrate exudation may account for the mechanism of efficient P acquisition by alkaline-tolerant L. pilosus well adapted to calcareous soils. Cluster-root formation and citrate exudation in L. pilosus can be altered by medium pH and P deficiency. Phosphorus deficiency-induced proton release may be associated with the reduced anion uptake, but high pH-induced proton release may be partly attributed to increased cation uptake. [ABSTRACT FROM AUTHOR]

Plants develop strategies to recycle phosphorus so that all organs receive adequate amounts of phosphorus, especially new growing organs. To evaluate the metabolic adaptation of rice plants under phosphorus deficient conditions, we selected several genes related to phosphorus utilization efficiency in the cell. Phosphoenolpyruvate carboxylase, triose phosphate translocator, phosphoenolpyruvate/phosphate translocator (PPT), pyruvate kinase, NAD dependent glyceraldehyde-3-phosphate dehydrogenase, and NADP dependent glyceraldehyde-3-phosphate dehydrogenase were selected because of their important roles in phosphorus utilization by the cell, and because they are part of the proposed bypass pathways by which the cells save phosphate. The most dramatic change was observed in the expression level of PPT (which transports phosphoenolpyruvate (PEP) from the cytosol into the chloroplast); thus we believe that PEP may play an important role in maintaining carbon metabolism under phosphate deficient conditions. [ABSTRACT FROM AUTHOR]

The study compared the release of protons by two genotypes (BAT477 and DOR364) of bean (Phaseolus vulgaris L.) relying on various sources of N (urea, nitrate and N2 fixation), at two levels of P supply: 1 μM (or 0 for urea-fed plants) and 25 μM. The plants grown at low P showed reduced growth and P concentration in tissues. The proton release was assessed at two levels: (i) at the whole plant level using pH-stat system in hydroponic culture; (ii) at the level of single roots by the combined use of agarose gel-dye indicator and videodensitometry measurements which provided information on the spatial variation of proton release along root axes. The pH-stat measurements showed that urea resulted in the greatest proton release while nitrate led to net hydroxyl release. Moreover, decreased proton release was observed at night for plants relying on urea and N2 fixation, while no diurnal pattern occurred for plants relying on nitrate. Phophorus deficiency increased proton release in urea-fed plants and decreased hydroxyl release in nitrate-fed plants. Conversely, N2-fixing plants showed an opposite behaviour, i.e. lower proton release at low than high P supply. Less effect of P supply on proton/hydroxyl release was found at the level of single root tips (videodensitometry experiment) in N2-fixing plants. Little genotypic difference in proton release was found although BAT477 showed a greater ability to respond to P deficiency than DOR364 when relying on urea or nitrate. Proton release of N2-fixing plants was greater in BAT477 than in DOR364, both at the whole plant and single root levels. [ABSTRACT FROM AUTHOR]

White lupin (Lupinus albus L.) acclimates to phosphorus deficiency (-P) by the development of short, densely clustered lateral roots called proteoid (or cluster) roots. These specialized plant organs display increased exudation of citric and malic acid. The enhanced exudation of organic acids from P stressed white lupin roots is accompanied by increased in vitro phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase (MDH) activity. Here we report the cloning of full-length white lupin PEPC and MDH cDNAs. RNA blot analysis indicates enhanced expression of these genes in -P proteoid roots, placing higher gene expression at the site of organic acid exudation. Correspondingly, macroarray analysis of about 1250 ESTs (expressed sequence tags) revealed induced expression of genes involved in organic acid metabolism in -P proteoid roots. In situ hybridization revealed that PEPC and MDH were both expressed in the cortex of emerging and mature proteoid rootlets. A C3 PEPC protein was partially purified from proteoid roots of P deficient white lupin. Native and subunit Mr were determined to be 440 kD and 110 kD, respectively. Citrate and malate were effective inhibitors of in vitro PEPC activity at pH 7. Addition of ATP partially relieved inhibition of PEPC by malate but had little effect on citrate inhibition. Taken together, the results presented here suggest that acclimation of white lupin to low P involves modified expression of plant genes involved in carbon metabolism. [ABSTRACT FROM AUTHOR]

The roots of white lupin (Lupinus albus L. cv. Kievskij mutant) secrete acid phosphatase, S-APase, when they grow under conditions of low available phosphorus (P). S-APases hydrolyze organic phosphate compounds in the rhizosphere and supply inorganic phosphate to the plants. Low phosphorus availability also induces vigorous growth of cluster roots. In this study, the function of cluster roots was investigated with reference to S-APase secretion. White lupins were grown in hydroponic culture in a greenhouse under P-deficient and P-sufficient conditions. S-APase in the excised roots after treatment was detected by staining with 4-methylumbelliferone phosphate (MUP). Gene expression of S-APase in cluster and normal roots was also investigated. Activity was greatest in the roots of plants grown under conditions of P -deficiency, particularly in cluster roots. S-APase gene expression was induced by a decrease in internal P concentrations, and was especially high in cluster roots formed under conditions of P -deficiency. It was suggested that decrease of internal P concentration stimulated both of the S-APase expression and cluster root formation. [ABSTRACT FROM AUTHOR]

A possible contribution of alterations in metabolic sequences involved in citrate catabolism, to intracellular accumulation and subsequent release of citrate was investigated in cluster roots of phosphorus (P)-deficient white lupin (Lupinus albus L.). Citrate accumulation during maturation of root clusters was associated with decreased levels of intracellular soluble Pi and ATP, and with reduced rates of respiration. Inhibitor studies with KCN and salicylhydroxamic acid (SHAM) suggest a reduced capacity of both the cytochrome pathway and of the alternative respiration with a concomitant decrease of immunochemically detectable protein levels of the alternative oxidase. Reduced respiration seems to be related to a general impairment of the respiratory system, rather than to limitation of respiratory substrates such as Pi and adenylates, as indicated by the absence of stimulatory effects of the uncoupler CCCP. The citrate/malate ratio in juvenile root clusters with high rates of respiration and low inherent levels of citrate accumulation was increased by short-term application (4–8 h) of azide and SHAM as respiration inhibitors. During maturation of root clusters, a shift from intracellular malic acid to citric acid accumulation was associated also with down-regulation of ATP citrate lyase (ACL), which catalyzes cleavage of citrate into acetyl-CoA and oxaloacetate with a putative function as anapleurotic source for the production of acetyl-CoA under P-deficient conditions. Inhibition of nitrate uptake and assimilation is a general response to P limitation in many plant species including white lupin. Reduced consumption of the amino acceptor 2-oxoglutaric acid as a product of citrate turnover may therefore contribute to increased citrate accumulation. Accordingly, artificial inhibition of nitrate reduction by localized application of tungstate significantly increased the citrate/malate ratio in juvenile root clusters. Lowering the cytosolic pH by external application of propionate stimulated citrate and malate exudation in non-cluster lateral roots and in developing root clusters. This effect was reverted by preincubation with phosphonate to buffer the cytosol. The results suggest that acidification of the cytosol may be an important factor, triggering the transient release of citrate and protons from mature root clusters in P-deficient white lupin. [ABSTRACT FROM AUTHOR]

Biomass accumulation by crops depends on both light interception by leaves and on the efficiency with which the intercepted light is usedto produce dry matter. Our aim was to identify which of these processes were affected for maize (Zea mays L., cv Volga) field crops grownunder phosphorus (P) deficiency. In the preceding paper (Plenet et al., 2000), it was shown that P deficiency severely reduced leaf growth. In this paper, the effect of P deficiency on the radiation-use efficiency (RUE) was investigated. The experimental work was carried outin 1995, 1996 and 1997 on a long-term P fertilisation trial located on a sandy soil in the south-west of France. Three P fertilisation regimes have been applied since 1972: no- P (P0 treatment) and different rates of P fertiliser (P1.5: 1.5 times the grain P export and P3: 3times the grain P export). These fertilisation regimes have led to contrasted levels of soil P supply. Only slight differences were observed between the P1.5 and P3 treatment for above-ground biomass accumulation and grain yield. Conversely the grain yield was significantly reduced in P0 (?11%). Above-ground biomass production was severely reduced, with the maximum difference between treatment (?60% in P0) occurring between 400 and 600 deg. C days after sowing. The lower biomass production in P0 was accounted for by the reduced amount of photosynthetically active radiation (PAR) absorbed by the canopy, which wasitself the consequence of the reduced leaf area index (see Plenet etal., 2000). The calculated RUE were found to depend on the plant stage, especially during the pre-flowering period, and on the average air temperature. No effect of P deficiency was observed on the calculated RUE, even during the period when above-ground biomass accumulationwas the most severely reduced. These results obtained in field crop conditions strengthen the idea that P deficiency affects plant growth, especially leaf growth, earlier and to a greater extent than photosynthesi [ABSTRACT FROM AUTHOR]

Biomass accumulation by crops depends both on light interception by leaves and on the efficiency with which the intercepted light is usedto produce dry matter. Our aim was to identify which of these processes were affected for maize (Zea Mays L., cv Volga) field crops grownunder phosphorus (P) deficiency, and assess their relative importance. In this paper, the effects of P deficiency on leaf appearance, leaf elongation rate, final individual leaf area and leaf senescence were studied. The experimental work was carried out in 1995-1977 on a long-term P fertilisation trial located on a sandy soil in the south-west of France. Three P fertilisation regimes have been applied since 1972: no-P (P0 treatment) and different rates of P fertiliser (P1.5:1.5 times the grain P export and P3:3 times the grain P export). These fertilisation regimes have led to contrasted levels of soil P supply,with the P0 treatment being limiting for growth. Very few differences were observed about leaf growth between the P1.5 and P3 treatments.Conversely, the leaf area index (LAI) was significantly reduced in the P0 treatment, especially during the first phases of the crop cycle(up to -60% between the 7- and 14-visible leaves). This effect gradually decreased over time. The lower LAI in P0 treatment was due to two main processes affecting the leaf growth. The final number of leaves per plant and leaf senescence were only slightly modified by P deficiency. Conversely, leaf appearance was delayed during the period between leaf 4 and leaf 9. The value of the phyllochron increased from 47 deg. C days in the P1.5 treatment to 65 deg. C days in the P0 treatment. Leaf elongation rates during the quasi-linear phase of leaf expansion were significantly reduced for lower leaves of P0 plants. Thefinal size of leaves L2-L12 was reduced. On the opposite, leaf elongation duration was not greatly affected by P treatments. Before the emergence of leaf 9, the reduction of individual leaf size was the main fact [ABSTRACT FROM AUTHOR]

"Root growth and architecture are important for phosphorus acquisition due to the relative immobility of P in the soil. Fractal geometry is a potential new approach to the analysis of root architecture. Substantial genetic variation in root growth and architecture has been observed in common bean. Common bean (Phaseolus vulgaris L.) genotypeswith contrasting root architecture were grown under moderate and lowP conditions in a field experiment. Linear and planar fractal dimension were measured by tracing root intercepts with vertical planes. Linear fractal dimension increased over time in efficient genotypes, but remained fairly constant over time in inefficient genotypes. Planarfractal dimension increased over time for all genotypes, but was higher in efficient than inefficient genotypes at the end of the experiment. Planar fractal dimension of medium P plants was found to correlate with shoot P content indicating fractal dimension to be a possibleindicator for root P uptake. The increasing fractal dimension over time indicates that fractal analysis is a sensitive measure of root branching intensity. A less destructive method for acquisition of data that allows for continuous analysis of fractal geometry and thereby screening for more P efficient genotypes in the field is suggested. This method will allow the researcher to conduct fractal analysis and still complete field trials with final yield evaluation. [ABSTRACT FROM AUTHOR]

A previous study found that increased phosphorus (P) supply to frequently defoliated white clover plants, growing in a low-P, dry soil, alleviated water stress symptoms and increased plant recovery on rewatering. In this study we determined how these stresses influence whiteclover growth. Measurements were made of the leaf canopy, stolon infrastructure and root system of the white clover plants growing in a low-P soil. Treatments included the factorial combination of four levels of P supply, two defoliation frequencies and two soil water treatments. White clover growth declined markedly when P-deficient plants were exposed to frequent defoliation and dry soil conditions. Leaf area was more affected than other parameters, in that the combination ofstresses reduced leaf area to 2% of maximum observed for infrequently defoliated plants growing in high-P soil, with adequate water. Increased P supply generally increased the growth of all plant parts. Frequently defoliated plants growing in dry soil produced similar or greater leaf mass and leaf area as plants from similar treatments growing in wet soil, when the P supply increased to 50 mg P kg-1 soil. Higher P rates were able to negate the effect of dry soil on these frequently defoliated plants, as a result of larger water and P uptake. Also, the frequently defoliated plants with restricted root growth did not respond to a small increase in P supply (17 mg P kg-1 soil) for the leaf growth, irrespective of whether they were growing in wet or dry soil. Infrequently defoliated plants with greater root growth, compared to frequently defoliated plants, more than doubled their leaf mass with this P treatment. [ABSTRACT FROM AUTHOR]

Root exudates were collected from radish and rape plants grown in P sufficient and P deficient nutrient solution. In radish, tartaric, malic and succinic acids were the dominant organic acids which increased between 15 times (succinic acid) and 60 times (malic acid) under P deficient conditions. In another experiment in quartz sand culture supplied with either Ca3(PO4)2 or AlPO4, radish utilized P from AlPO4 much better than from Ca3(PO4)2 whereas the opposite was true for rape. The results demonstrated the role of a particular organic acid in mobilizing sparingly soluble P and were in accordance with the preferential growth of two plants on acid (radish) and calcareous (rape) soils in China. [ABSTRACT FROM AUTHOR]

Phosphorus (P) deficiency increased the secretion of phytases from roots of various plant species. The secretory phytases were collected with a dialysis membrane tube for 24 hours from roots of sixteen plant species grown with low or adequate supply of P in nutrient solutions. The activity of not only secretory phytase, but also acid phosphatase, increased with the low P treatment in all of the plant species examined. Secretion of phytase by the roots under P-deficient conditions was highest in Brachiaria decumbens CIAT 606, Stylosanthes guianensis CIAT 184 and tomato, moderate in Brachiaria brizantha CIAT6780, Stylosanthes guianensis CIAT 2950, alfalfa, white clover and orchard grass, and lowest in Andropgon gayanus CIAT 621, Stylosanthes capitataCIAT 10280, upland rice, timothy, redtop, alsike clover, red clover and white lupin plants. An immunoreactive protein band that reacted with a polyclonal antibody raised against wheat bran phytase, corresponding to molecular weight 35-40 kD, could be detected in seven of thespecies tested. These results indicate that the secretory phytase may provide an efficient mechanism for certain plants to utilize inositol hexaphosphate in soil. [ABSTRACT FROM AUTHOR]