P-acquisition Efficiency Research Articles

Differential response of phosphorus utilization efficiency in rice by tracer technique using phosphorus-32 under phosphorus stress environment

In most soils, soil and fertilizer Phosphorus (P) are easily bound by either soil organic matter or chemicals and thus are unavailable to plants unless hydrolyzed to release inorganic phosphate. Therefore, the development of P-efficient rice varieties that can grow and yield better with low P supply is a key to improve crop production. P efficient plants play a major role in increasing crop yields due to shortage of inorganic P fertilizer resources, limited land and water resources and increasing environmental concerns. Based on the P uptake efficiency, four rice genotypes viz.,TNRH 180, CB08504, CB06732 and ADT 47 were selected from the field experiment and used in pot culture experiment with three levels of P using radio isotope technique to quantify the P acquisition efficiency (PAE) and P use efficiency (PUE) and also to determine the native P supplying power of the soils using 32P in low P soils. Growth and yield parameters, grain and straw yield and major nutrients uptake of rice genotypes were increased with enhanced level of phosphorus application. Among the four genotypes, TNRH 180 recorded the highest grain yield and uptake. Increasing the P application rate from 25 to 50 kg P2O5 ha-1 increased the %Pdff in grain and straw for all the genotypes. The mean per cent phosphorus utilization (PPU) ranged between 18.74 and 23.72. The PPU of the genotypes followed the order TNRH 180 (23.72 %) > CB08504 (23.36 %) > CB06732 (20.54%) > ADT 47 (18.74%). The PPU values were higher at lower level of P application (25 kg P2O5 ha-1) for the genotypes TNRH 180, CB08504 and CB06732. From this study showed that rice genotypes have the ability to utilize the both available and unavailable form of phosphorus by secreting some organic acids in the root portion to solubilize. Hence rice genotypes indicated above have the ability to increase phosphorus utilization efficiency.

Reprint of “Developing phosphorus-efficient crop varieties—An interdisciplinary research framework”

Crop production relies on continuous input of large amounts of phosphorus (P) in form of mineral fertilisers manufactured from phosphate rock (PR), a finite resource likely to be depleted within a century. Developing crop varieties with enhanced efficiency for P will make a key contribution to sustainable use of P resources. Crop yield (Yseed) in the context of nutrient-use efficiency can be expressed as a function of total accumulated nutrient in the plant (Nutaccum), nutrient harvest index (NutHI, the fraction of total accumulated nutrient in the plant that is allocated to the seed), and seed nutrient concentration (%Nutseed): Yseed=Nutaccum (NutHI/%Nutseed). In this paper, we review the physiological traits and processes affecting the components of this simple model for improving the P-use efficiency of crops, with a particular focus on root architectural traits for enhancing P-acquisition efficiency (PAE) and hence Nutaccum. As field-grown crops commonly encounter a combination of various abiotic stresses, the potentially negative effects of root architectural traits for improved P acquisition on crop water uptake are also considered.Given that P efficiency at whole-plant level is a complex multi-genic trait governed by interactions between genetic, environmental, and management factors (G×E×M), we then highlight the potential and limitations of root architectural and crop simulation models for evaluating the utility of root adaptive traits for P uptake and crop yield. Furthermore, the application of crop models for assessing the long-term impacts of P-efficient genotypes on soil P dynamics and productivity of cropping systems under current and future climatic conditions is addressed. We then present the components of an interdisciplinary research framework for exploiting genetic diversity in root traits for developing new P-efficient crop varieties and cropping systems in order to (i) lower the critical soil-P levels for optimum crop yields, thereby allowing crop production at lower soil-P loads, (ii) improve the internal P-cycling and crop productivity in low-input and organic cropping systems, (iii) reduce the inefficient use of P fertilisers in fertilised and intensive systems, (iv) improve the environmental sustainability of cropping systems by reducing the potential risk of soil-P losses to water bodies.

Genetic Architecture of Phosphorus Use Efficiency in Tropical Maize Cultivated in a Low‐P Soil

ABSTRACTPhosphorus (P) deficiency is a major limiting factor for crop production in several countries. A better understanding of the genetic components of P use efficiency (PUE) is required to improve crop performance in low‐P soils. To date, no QTLs (quantitative trait loci) were mapped for PUE using grain yield and other late phenotypic data in tropical conditions. Thus, we evaluated the genetic architecture of PUE in tropical maize (Zea mays L.) using multiple interval mapping for design III in a population of 140 RILs (recombinant inbred lines) backcrossed with both parental lines. The parental lines contrasted for yield and for PUE, a phenotypic index that was further decomposed into P acquisition efficiency (PAE) and P utilization efficiency. Our results showed that dominance effects were more important than additive effects for explaining the variations in PUE and its components. Approximately 80% of the QTLs mapped for PAE co‐localized with those for PUE, indicating that the efficiency in acquiring P is the main determinant of PUE in tropical maize. Also, QTLs for PUE and PAE were located near to candidate genes previously associated with root development. Thus, we present important information to guide breeding strategies for the development of maize cultivars more adapted to P deficiency.

Developing phosphorus-efficient crop varieties—An interdisciplinary research framework

Crop production relies on continuous input of large amounts of phosphorus (P) in form of mineral fertilisers manufactured from phosphate rock (PR), a finite resource likely to be depleted within a century. Developing crop varieties with enhanced efficiency for P will make a key contribution to sustainable use of P resources. Crop yield (Yseed) in the context of nutrient-use efficiency can be expressed as a function of total accumulated nutrient in the plant (Nutaccum), nutrient harvest index (NutHI, the fraction of total accumulated nutrient in the plant that is allocated to the seed), and seed nutrient concentration (%Nutseed): Yseed=Nutaccum (NutHI/%Nutseed). In this paper, we review the physiological traits and processes affecting the components of this simple model for improving the P-use efficiency of crops, with a particular focus on root architectural traits for enhancing P-acquisition efficiency (PAE) and hence Nutaccum. As field-grown crops commonly encounter a combination of various abiotic stresses, the potentially negative effects of root architectural traits for improved P acquisition on crop water uptake are also considered.Given that P efficiency at whole-plant level is a complex multi-genic trait governed by interactions between genetic, environmental, and management factors (G×E×M), we then highlight the potential and limitations of root architectural and crop simulation models for evaluating the utility of root adaptive traits for P uptake and crop yield. Furthermore, the application of crop models for assessing the long-term impacts of P-efficient genotypes on soil P dynamics and productivity of cropping systems under current and future climatic conditions is addressed. We then present the components of an interdisciplinary research framework for exploiting genetic diversity in root traits for developing new P-efficient crop varieties and cropping systems in order to (i) lower the critical soil-P levels for optimum crop yields, thereby allowing crop production at lower soil-P loads, (ii) improve the internal P-cycling and crop productivity in low-input and organic cropping systems, (iii) reduce the inefficient use of P fertilisers in fertilised and intensive systems, (iv) improve the environmental sustainability of cropping systems by reducing the potential risk of soil-P losses to water bodies.

Phosphorus acquisition and internal utilization efficiency among maize landraces from the central Mexican highlands

In many low input maize production systems phosphorus (P) is in limited supply. Improved crops that acquire and use P more efficiently are a sustainable solution to increase crop yield in these systems. This study determined the contribution of P acquisition efficiency (PAE) and P utilization efficiency (PUTE) in determining P use efficiency (PUE) of 20 maize accessions from the Purhepecha Plateau, Michoacan, grown on a P-deficient Andisol, at two locations with low (23kgP2O5ha−1) and high (97kgP2O5ha−1) P fertilization under rain-fed conditions. Under P deficiency conditions in the acid soil, both PAE and PUTE were important factors explaining the variation in P use efficiency at both P levels. Greater P use efficiency was related to an improved distribution of dry matter in the plants and a lower absorbed P allocated in the grain. Low grain P concentrations at maturity were not associated with reductions in grain yield, nor were they significantly correlated to HI, suggesting that exploiting genotypic variation for this trait may be productive. The study identified genetic variation among maize landraces in their response of PUTE. On a P-deficient acidic soil, accessions CB-2, DP×Tromba, HV313×DEM, Macho III-04, and CIMMYT-1, were categorized as the most P efficient and the most responsive to increased P availability. In contrast, late maturing P-efficient accessions SHUI-2, CB-2, AS-4, and ZR-6 showed the greatest variation for P uptake under low P conditions. Late maturity improved growth and yield in low P soils. These accessions expressed the desired traits for PUE, which may be exploited in breeding efforts.

Opportunities for improving phosphorus‐use efficiency in crop plants

Limitation of grain crop productivity by phosphorus (P) is widespread and will probably increase in the future. Enhanced P efficiency can be achieved by improved uptake of phosphate from soil (P-acquisition efficiency) and by improved productivity per unit P taken up (P-use efficiency). This review focuses on improved P-use efficiency, which can be achieved by plants that have overall lower P concentrations, and by optimal distribution and redistribution of P in the plant allowing maximum growth and biomass allocation to harvestable plant parts. Significant decreases in plant P pools may be possible, for example, through reductions of superfluous ribosomal RNA and replacement of phospholipids by sulfolipids and galactolipids. Improvements in P distribution within the plant may be possible by increased remobilization from tissues that no longer need it (e.g. senescing leaves) and reduced partitioning of P to developing grains. Such changes would prolong and enhance the productive use of P in photosynthesis and have nutritional and environmental benefits. Research considering physiological, metabolic, molecular biological, genetic and phylogenetic aspects of P-use efficiency is urgently needed to allow significant progress to be made in our understanding of this complex trait.

Genotypic variation in phosphorus acquisition from sparingly soluble P sources is related to root morphology and root exudates in Brassica napus

Genotypic variations in the adaptive response to low-phosphorus (P) stress and P-uptake efficiency have been widely reported in many crops. We conducted a pot experiment to evaluate the P-acquisition ability of two rapeseed (Brassica napus) genotypes supplied with two sparingly soluble sources of P, Al-P and Fe-P. Then, the root morphology, proton concentrations, and carboxylate content were investigated in a solution experiment to examine the genotypic difference in P-acquisition efficiency. Both genotypes produced greater biomass and accumulated more P when supplied with Al-P than when supplied with Fe-P. The P-efficient genotype 102 showed a significantly greater ability to deplete sparingly soluble P from the rhizosphere soil because of its greater biomass and higher P uptake compared with those of the P-inefficient genotype 105. In the solution experiment, the P-efficient genotype under low-P conditions developed dominant root morphological traits, and it showed more intensive rhizosphere acidification because of greater H(+) efflux, higher H(+)-ATPase activity, and greater exudation of carboxylates than the P-inefficient genotype. Thus, a combination of morphological and physiological mechanisms contributed to the genotypic variation in the utilization of different sparingly soluble P sources in B. napus.

Phosphate utilization efficiency correlates with expression of low-affinity phosphate transporters and noncoding RNA, IPS1, in barley.

Genetic variation in phosphorus (P) efficiency exists among wheat (Triticum aestivum) and barley (Hordeum vulgare) genotypes, but the underlying mechanisms for the variation remain elusive. High- and low-affinity phosphate (Pi) PHT1 transporters play an indispensable role in P acquisition and remobilization. However, little is known about genetic variation in PHT1 gene expression and association with P acquisition efficiency (PAE) and P utilization efficiency (PUE). Here, we present quantitative analyses of transcript levels of high- and low-affinity PHT1 Pi transporters in four barley genotypes differing in PAE. The results showed that there was no clear pattern in the expression of four paralogs of the high-affinity Pi transporter HvPHT1;1 among the four barley genotypes, but the expression of a low-affinity Pi transporter, HvPHT1;6, and its close homolog HvHPT1;3 was correlated with the genotypes differing in PUE. Interestingly, the expression of HvPHT1;6 and HvPHT1;3 was correlated with the expression of HvIPS1 (for P starvation inducible; noncoding RNA) but not with HvIPS2, suggesting that HvIPS1 plays a distinct role in the regulation of the low-affinity Pi transporters. In addition, high PUE was found to be associated with high root-shoot ratios in low-P conditions, indicating that high carbohydrate partitioning into roots occurs simultaneously with high PUE. However, high PUE accompanying high carbon partitioning into roots could result in low PAE. Therefore, the optimization of PUE through the modification of low-affinity Pi transporter expression may assist further improvement of PAE for low-input agriculture systems.

Arbuscular mycorrhizal fungus enhances P acquisition of wheat (Triticum aestivum L.) in a sandy loam soil with long-term inorganic fertilization regime

The P efficiency, crop yield, and response of wheat to arbuscular mycorrhizal fungus (AMF) Glomus caledonium were tested in an experimental field with long-term (19years) fertilizer management. The experiment included five fertilizer treatments: organic amendment (OA), half organic amendment plus half mineral fertilizer (1/2 OM), mineral fertilizer NPK, mineral fertilizer NK, and the control (without fertilization). AMF inoculation responsiveness (MIR) of wheat plants at acquiring P were estimated by comparing plants grown in unsterilized soil inoculated with G. caledonium and in untreated soil containing indigenous AMF. Without AMF inoculation, higher crop yields but lower colonization rates were observed in the NPK and two OA-inputted treatments, and NPK had significantly (P < 0.05) lower impacts on organic C and available P in soils and thereby P acquisition of wheat plants compared with OA and 1/2 OM. G. caledonium inoculation significantly (P < 0.05) increased colonization rates with the NPK and two P-deficient treatments but significantly (P < 0.05) increased vegetative biomass, crop yield, and P acquisition of wheat as well as soil alkaline phosphatase (ALP) activity, only with the NPK treatment. This gave an MIR of ca. 45% on total P acquisition of wheat plants. There were no other remarkable MIRs. It suggested that the MIR is determined by soil available P status, and rational combination of AMF with chemical NPK fertilizer can compensate for organic amendments by improving P-acquisition efficiency in arable soils.

Carboxylate release of wheat, canola and 11 grain legume species as affected by phosphorus status

The capacity of plant roots to increase their carboxylate exudation at a low plant phosphorus (P) status is an adaptation to acquire sufficient P at low soil P availability. Our objective was to compare crop species in their adaptive response to a low-P availability, in order to gain knowledge to be used for improving crop P-acquisition efficiency from soils that are low in P or that have a high capacity to retain P. In the present screening study we compared 13 crop species, grown in sand at either 3 or 300 μM of P, and measured root mass ratio, cluster-root development, rhizosphere pH and carboxylate composition of root exudates. Root mass ratio decreased with increasing P supply for Triticum aestivum L., Brassica napus L., Cicer arietinum L. and Lens culinaris Medik., and increased only for Pisum sativum L., while the Lupinus species and Vicia faba L. were not responsive. Lupinus species that had the potential to produce root clusters either increased or decreased biomass allocation to clusters at 300 μM of P compared with allocation at 3 μM of P. All Lupinus species acidified their rhizosphere more than other species did, with average pH decreasing from 6.7 (control) to 4.3 for Lupinus pilosus L. and 5.9 for Lupinus atlanticus L.; B. napus maintained the most alkaline rhizosphere, averaging 7.4 at 300 μM of P. Rhizosphere carboxylate concentrations were lowest for T. aestivum, B. napus, V. faba, and L. culinaris than for the other species. Exuded carboxylates were mainly citrate and malate for all species, with the exception of L. culinaris and C. arietinum, which produced mainly citrate and malonate. Considerable variation in the concentration of exuded carboxylates and protons was found, even with a genus. Cluster-root forming species did not invariably have the highest concentrations of rhizosphere carboxylates. Lupinus species varied both in P-uptake and in the sensitivity of their cluster-root development to external P supply. Given the carbon cost of cluster roots, a greater plasticity in their formation and exudation (i.e. reduced investment in cluster roots and exudation at higher soil P, a negative feedback response) is a desirable trait for agricultural species that may have variable access to readily available P.

Corrigendum to: Genetic mapping of basal root gravitropism and phosphorus acquisition efficiency in common bean.

Root gravitropism determines the relative distribution of plant roots in different soil layers, and therefore, may influence the acquisition of shallow soil resources such as phosphorus (P). Growth pouch and field studies were conducted to evaluate root gravitropism of common bean (Phaseolus vulgaris L.) in response to P deficiency and to detect quantitative trait loci (QTL) associated with this trait. A deep-rooted genotype, DOR364, was crossed with a shallow-rooted genotype, G19833, to obtain 86 F5.7 recombinant inbred lines (RILs). Root gravitropic traits were measured as basal root growth angle (BRGA), shallow basal root length (SBRL, basal root length in the top 0-3 cm of soil) and relative shallow basal root length (RSBRL, percentage of basal root length in the top 0-3 cm of soil relative to total basal root length). Large genetic variability for these traits was found in the parents and RILs, with BRGA ranging from -18.73 to 56.69º and SBRL ranging from 0.42 to 2.63 m per plant. The parents and six RILs with contrasting root gravitropism were further evaluated in the field, where root shallowness was significantly correlated with plant growth and P uptake. QTL were detected by single point analysis (SPA), interval mapping (IM) and composite interval mapping (CIM) techniques with a genetic map for the DOR364 × G19833 population consisting of 236 molecular markers. The IM/CIM QTL were detected among the 11 linkage groups of common bean, with 16 QTL controlling the above root traits and six QTL controlling P acquisition efficiency (PAE) in the field study. At least three of the root trait QTL were associated with QTL for PAE, suggesting that root gravitropic traits are associated with PAE and that QTL for these traits can be used to facilitate selection and breeding for higher P efficiency in common bean and other crops.

Genetic mapping of basal root gravitropism and phosphorus acquisition efficiency in common bean.

Root gravitropism determines the relative distribution of plant roots in different soil layers, and therefore, may influence the acquisition of shallow soil resources such as phosphorus (P). Growth pouch and field studies were conducted to evaluate root gravitropism of common bean (Phaseolus vulgaris L.) in response to P deficiency and to detect quantitative trait loci (QTL) associated with this trait. A deep-rooted genotype, DOR364, was crossed with a shallow-rooted genotype, G19833, to obtain 86 F5.7 recombinant inbred lines (RILs). Root gravitropic traits were measured as basal root growth angle (BRGA), shallow basal root length (SBRL, basal root length in the top 0-3 cm of soil) and relative shallow basal root length (RSBRL, percentage of basal root length in the top 0-3 cm of soil relative to total basal root length). Large genetic variability for these traits was found in the parents and RILs, with BRGA ranging from -18.73 to 56.69º and SBRL ranging from 0.42 to 2.63 m per plant. The parents and six RILs with contrasting root gravitropism were further evaluated in the field, where root shallowness was significantly correlated with plant growth and P uptake. QTL were detected by single point analysis (SPA), interval mapping (IM) and composite interval mapping (CIM) techniques with a genetic map for the DOR364 × G19833 population consisting of 236 molecular markers. The IM / CIM QTL were detected among the 11 linkage groups of common bean, with 16 QTL controlling the above root traits and six QTL controlling P acquisition efficiency (PAE) in the field study. At least three of the root trait QTL were associated with QTL for PAE, suggesting that root gravitropic traits are associated with PAE and that QTL for these traits can be used to facilitate selection and breeding for higher P efficiency in common bean and other crops.

Strategies to isolate transporters that facilitate organic anion efflux from plant roots

The efflux of organic anions from roots plays an important role in plant nutrition. The release of simple carboxylic anions such as citrate, malate and oxalate have been implicated in mechanisms of aluminium (Al) tolerance and improved acquisition of soil phosphorus. These metabolites are likely to cross cell membranes as multivalent anions and recent evidence indicates that anion-permeable channels facilitate this flow in the Al-dependent efflux of malate and citrate from wheat and maize, respectively. However, the genes encoding these anion channels, or any other protein that facilitates the release of citrate, malate or oxalate have not been isolated. This is an obstacle for the application of biotechnology to combat Al toxicity and to improve P-acquisition efficiency in plants. We discuss several strategies aimed at isolating genes that facilitate organic anion release from plant roots.