P-uptake Efficiency Research Articles

A conceptual model of root hair ideotypes for future agricultural environments: what combination of traits should be targeted to cope with limited P availability?

Phosphorus (P) often limits crop production and is frequently applied as fertilizer; however, supplies of quality rock phosphate for fertilizer production are diminishing. Plants have evolved many mechanisms to increase their P acquisition, and an understanding of these traits could result in improved long-term sustainability of agriculture. This Viewpoint focuses on the potential benefits of root hairs to sustainable production. First the various root-related traits that could be deployed to improve agricultural sustainability are catalogued, and their potential costs and benefits to the plant are discussed. A novel mathematical model describing the effects of length, density and longevity of root hairs on P acquisition is developed, and the relative benefits of these three root-hair traits to plant P nutrition are calculated. Insights from this model are combined with experimental data to assess the relative benefits of a range of root hair ideotypes for sustainability of agriculture. A cost-benefit analysis of root traits suggests that root hairs have the greatest potential for P acquisition relative to their cost of production. The novel modelling of root hair development indicates that the greatest gains in P-uptake efficiency are likely to be made through increased length and longevity of root hairs rather than by increasing their density. Synthesizing this information with that from published experiments we formulate six potential ideotypes to improve crop P acquisition. These combine appropriate root hair phenotypes with architectural, anatomical and biochemical traits, such that more root-hair zones are produced in surface soils, where P resources are found, on roots which are metabolically cheap to construct and maintain, and that release more P-mobilizing exudates. These ideotypes could be used to inform breeding programmes to enhance agricultural sustainability.

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.

Can differences in phosphorus uptake kinetics explain the distribution of cattail and sawgrass in the Florida Everglades?

BackgroundCattail (Typha domingensis) has been spreading in phosphorus (P) enriched areas of the oligotrophic Florida Everglades at the expense of sawgrass (Cladium mariscus spp. jamaicense). Abundant evidence in the literature explains how the opportunistic features of Typha might lead to a complete dominance in P-enriched areas. Less clear is how Typha can grow and acquire P at extremely low P levels, which prevail in the unimpacted areas of the Everglades.ResultsApparent P uptake kinetics were measured for intact plants of Cladium and Typha acclimated to low and high P at two levels of oxygen in hydroponic culture. The saturated rate of P uptake was higher in Typha than in Cladium and higher in low-P acclimated plants than in high-P acclimated plants. The affinity for P uptake was two-fold higher in Typha than in Cladium, and two- to three-fold higher for low-P acclimated plants compared to high-P acclimated plants. As Cladium had a greater proportion of its biomass allocated to roots, the overall uptake capacity of the two species at high P did not differ. At low P availability, Typha increased biomass allocation to roots more than Cladium. Both species also adjusted their P uptake kinetics, but Typha more so than Cladium. The adjustment of the P uptake system and increased biomass allocation to roots resulted in a five-fold higher uptake per plant for Cladium and a ten-fold higher uptake for Typha.ConclusionsBoth Cladium and Typha adjust P uptake kinetics in relation to plant demand when P availability is high. When P concentrations are low, however, Typha adjusts P uptake kinetics and also increases allocation to roots more so than Cladium, thereby improving both efficiency and capacity of P uptake. Cladium has less need to adjust P uptake kinetics because it is already efficient at acquiring P from peat soils (e.g., through secretion of phosphatases, symbiosis with arbuscular mycorrhizal fungi, nutrient conservation growth traits). Thus, although Cladium and Typha have qualitatively similar strategies to improve P-uptake efficiency and capacity under low P-conditions, Typha shows a quantitatively greater response, possibly due to a lesser expression of these mechanisms than Cladium. This difference between the two species helps to explain why an opportunistic species such as Typha is able to grow side by side with Cladium in the P-deficient Everglades.

Variation in morphological and physiological parameters in herbaceous perennial legumes in response to phosphorus supply

Change in morphological and physiological parameters in response to phosphorus (P) supply was studied in 11 perennial herbaceous legume species, six Australian native (Lotus australis, Cullen australasicum, Kennedia prorepens, K. prostrata, Glycine canescens, C. tenax) and five exotic species (Medicago sativa, Lotononis bainesii, Bituminaria bituminosa var albomarginata, Lotus corniculatus, Macroptilium bracteatum). We aimed to identify mechanisms for P acquisition from soil. Plants were grown in sterilised washed river sand; eight levels of P as KH2PO4 ranging from 0 to 384 μg P g−1 soil were applied. Plant growth under low-P conditions strongly correlated with physiological P-use efficiency and/or P-uptake efficiency. Taking all species together, at 6 μg P g−1 soil there was a good correlation between P uptake and both root surface area and total root length. All species had higher amounts of carboxylates in the rhizosphere under a low level of P application. Six of the 11 species increased the fraction of rhizosphere citrate in response to low P, which was accompanied by a reduction in malonate, except L. corniculatus. In addition, species showed different plasticity in response to P-application levels and different strategies in response to P deficiency. Our results show that many of the 11 species have prospects for low-input agroecosystems based on their high P-uptake and P-use efficiency.

Variation in early phosphorus-uptake efficiency among wheat genotypes grown on two contrasting Australian soils

Seedlings from 198 wheat genotypes were screened in glasshouse trials for early biomass production (49 days after sowing, DAS) in a soil high in total phosphorus (P) but low in plant-available P. Fifteen hexaploid bread wheats were then examined more closely for early biomass production on 2 low-P soils: a highly P-fixing Ferrosol (1.3 mg resin-extractable P/kg) and a Red Kandosol (5.2 mg resin-extractable P/kg). The soils were either unamended for P or supplemented with sufficient P for maximum growth. Single lines of rye, triticale, and durum wheat were included for comparison. The plants were harvested at 21 and 35 DAS, and shoot biomass, root biomass, P content, and root length were measured. Shoot biomass was correlated with the P content of the seed in both unamended soils at the first harvest but only in the Ferrosol at the second harvest. There were no correlations between seed P and shoot biomass in the high-P treatments at either harvest. Genotypes were compared with one another by plotting shoot biomass from the high-P treatment against shoot biomass from the low-P treatment. Phosphorus-efficient genotypes were defined as those with relatively greater biomass at low P, while genotypes with a high biomass potential were defined as those able to accumulate relatively more biomass at high P. Two hexaploid wheats, Kukri and Vigour 18, were ranked as being P-efficient genotypes with a high biomass potential on both soils, while Halberd, CD87, and Katepwa were P-inefficient on both soils. Biomass accumulation for each genotype was compared with their root biomass, root : shoot ratio, specific root length and P-uptake efficiency. The strongest correlation across all treatments occurred between shoot biomass and root biomass. We discuss factors that may contribute to the variation in P-uptake efficiency among the genotypes.

The dynamics of phosphorus retention during an eight-year P-addition in a Neotropical headwater stream

Understanding the capacity of stream ecosystems to retain nutrients through physical-chemical processes and biotic assimilation has been a central goal of stream ecologists for decades. Currently, most of our understanding of nutrient saturation is based on short-term (<1 day) nutrient addition experiments, while predicting total stream ecosystem response to long-term anthropogenic nutrient loading requires considering the stream’s capacity to remove nutrients over extended periods. Dissolved phosphorus (P) retention results from a combination of biotic and abiotic mechanisms, which could follow different trajectories through time. Short-term biotic P uptake by algae and heterotrophic microbes typically involves direct assimilation from the water column and is saturated at low background soluble reactive phosphorus (SRP) levels (MULHOLLAND et al. 1990). However, during long-term P-loading, the biotic community could also respond by increasing biomass (PETERSON et al. 1985, SLAVIK et al. 2004, but see GREENWOOD & ROSEMOND 2005), temporarily increasing the community’s P-retention capacity. Abiotic P-sorption is an equilibrium process controlled by the relative concentrations of sorbed-P and dissolved-P, although it also depends on sediment size, iron, aluminum, organic content, and pH (MEYER 1979). During long-term P-loading, sediment should become increasingly P-saturated, decreasing abiotic retention. Because biotic and abiotic P-uptake mechanisms could have opposite responses to long-term Ploading, the relative importance of each mechanism will control a stream’s retention capacity over time. Specifically, where P-uptake is dominated by biotic pathways, streams could become temporarily more efficient at removing dissolved-P, whereas where P-uptake is primarily abiotic, streams potentially become less efficient. Here we present data from an 8-year experimental P-addition in a first-order stream, the Carapa, at La Selva Biological Station, Costa Rica. Previous experiments of P-dynamics in the Rio Salto at La Selva indicate that most uptake of P due to the input of naturally P-enriched regional groundwater is due to abiotic sorption (TRISKA et al. 2006). Biweekly measurements of dissolved P concentration upstream and at 3 downstream stations during the long-term P-injection in the Carapa allowed us to calculate P-uptake rates over the 8-year study. Assuming a dominance of abiotic control, we predicted that sediments would become saturated over time, decreasing Puptake efficiency.

Variation in Phosphorus Uptake and Use Efficiencies Between Pigeonpea Genotypes and Cowpea

ABSTRACT Low bioavailability of soil phosphorus (P) often limits N2 (nitrogen) fixation and crop production in large parts of the tropics. The efficiency of P acquisition and P use by 21 genotypes of pigeonpea [Cajanus cajan (L.) Millsp.] were studied in a pot experiment using two cowpea [Vigna unguiculata (L.) Waip.] genotypes as controls. The short-duration genotypes produced more dry matter, accumulated more P, and produced more dry matter per unit of absorbed P than the medium-and long-duration genotypes. Dry-matter production correlated positively with the P uptake (r2 = 0.72) and P-use efficiency (r2 = 0.86). The P uptake correlated positively with the P-use efficiency (r2 = 0.36); whereas the P-use efficiency correlated negatively with the P-uptake efficiency (r2 = 0.50). Root surface did not determine P acquisition of pigeonpea, which absorbed 1.6 mg P cm−3 from 33 cm3 soil compared with 0.17 mg P cm−3 from 387 cm3 soil for cowpea at 66 d.

Responses of Lentil to Co-Inoculation with Phosphate-Solubilizing Rhizobial Strains and Arbuscular Mycorrhizal Fungi

ABSTRACT The purpose of this study was to evaluate the responses of lentil (Lens culinariscv. ‘Ziba’) to co-inoculation with arbuscular mycorrhizal (AM) fungi and some indigenous rhizobial strains varying in phosphorus (P)-solubilizing ability in a calcareous soil with high pH and low amounts of available P and nitrogen (N). A factorial experiment with completely randomized block design was conducted under controlled greenhouse conditions. The treatments consisted of (1) three inoculants of Rhizobium leguminosarum bv. viciae strains and a mixed rhizobial inoculant with an effective P-solubilizer strain of Mesorhizobium ciceri, (2) two AM fungal species, Glomus mosseae and Glomus intraradices, (3) two P sources, superphosphate and phosphate rock. Four replications were prepared for each treatment and a related control. After the growth period of three months, the dry matter of shoots plus seeds, their P and N contents, and percent of root colonized by AM fungus were measured. The results showed that the effects of AM fungi, rhizobial strains, and P fertilizers were highly significant (p < 0.01) for all the characteristics studied. The rhizobial strain with P-solubilizing ability showed a more beneficial effect on plant growth and nutrient uptake than the strain without this ability, although both strains had similar effectiveness for N2-fixation in symbiosis with lentil. Synergistic relationships were observed between AM fungi and some rhizobial strains that related to the compatible pairing of these two microsymbionts. The P-uptake efficiency was increased when P fertilizers were applied along with AM fungi and/or P-solubilizer rhizobial strains.

Phosphorus and Micronutrient Nutrition of Chickpea Genotypes in a Multi-Nutrient-Deficient Typic Ustochrept

ABSTRACT The chickpea breeding program in India has not yet considered the genotypic variation in phosphorus (P) efficiency, despite the fact that the largest proportion of chickpea-growing soils are P deficient. Since general P application to chickpea is at sub-optimum levels, efficient P-utilizing genotypes will perform better than others under P-deficient conditions. High levels of P application may induce zinc (Zn) deficiency in plants grown on Zn-deficient soils. Twenty chickpea genotypes were evaluated for their P efficiency at varied levels of added P, and the effect of P levels on Zn, iron (Fe), copper (Cu), and manganese (Mn) nutrition was studied in pot-culture experiments. Three criteria were used for evaluating P efficiency; shoot dry-matter yield without P, P-uptake efficiency (PUPE), and P-utilization efficiency (PUSE). Under P-deficiency conditions (control), the genotypes BG-256, HK-94-134, Phule-G-5, and Vikash produced the highest shoot biomass. However, genotypes that were found to be superior in the absence of P did not perform in a similar way under optimum P supply. Root dry weight showed a highly significant correlation with P uptake at all P levels. In the case of PUPE, genotypes KPG-59 and Pusa-209 were found to be superior to others. With increasing P levels, PUSE declined in all the genotypes. Increasing P up to 13.5 mg kg−1 soil increased Zn concentration, while further increase led to decreased concentration. Genotypes KPG-59, BG-256, RSG-888, and JG-315 showed Zn concentrations below the critical limit of 20 μg Zn g−1 dry weight (DW) at the high level of P application (27.0 mg kg−1). Iron concentration decreased with increasing P levels. Up to 13.5 mg kg−1 P application, Cu concentration increased and thereafter decreased. Manganese concentration gradually increased with the increasing P levels studied. Based on three criteria, BG-256 can be recommended for use in P-deficient conditions and can be good germplasm source material for chickpea-breeding programs for evolving P-efficient genotypes. Results also suggest that when selecting P-efficient genotypes of chickpea, it is essential to apply deficient micronutrients.

Exudation of organic anions by roots of cabbage, carrot, and potato as influenced by environmental factors and plant age

AbstractA previous study demonstrated that cabbage was P efficient compared to carrot and potato. However, calculating plant P uptake by a mechanistic simulation model based on P transport by diffusion and mass flow, P uptake of roots according to the Michaelis‐Menten kinetics, and morphological root characteristics including root hairs, revealed that these parameters could explain only 2/5 of the total P uptake of cabbage, but 4/5 of that of carrot and potato (Dechassa et al., 2003). Therefore, it was hypothesized that a higher root exudation of organic anions may enhance P mobilization and hence P uptake of cabbage. The objective of this research was to determine root exudation of organic anions by the three species, and to investigate the influence of plant age and dark/light period on organic‐anion exudation by cabbage. Experiments were conducted in a growth chamber in nutrient solution with or without P. Organic anions were determined in root exudates and in root tissue. With cabbage and potato, P deficiency induced exudation of citrate and succinate, respectively. Citrate‐exudation rate of P‐deficient cabbage plants was correlated with accumulation of citrate in root tissue. In contrast, high succinate‐exudation rates in potato were not correlated with an increased concentration in root tissue. For carrot, no change was observed in the exudation of any of the organic anions in response to P deficiency. The results also showed that succinate‐ and citrate‐exudation rates of cabbage roots increased with increased plant age. There was also a significant increase in exudation rates of organic anions of cabbage roots during the light period of the day. It was concluded that cabbage had the ability to exude large amounts of citrate in response to P deficiency by which it can additionally enhance its P‐uptake efficiency, whereas carrot and potato showed little evidence of possessing such a mechanism.

Buckwheat ( Fagopyrum esculentum Moench) has high capacity to take up phosphorus (P) from a calcium (Ca)-bound Source

Two experiments were carried out in a growth chamber to investigate the phosphorus (P)-uptake efficiency of Fagopyrum esculentum Moench (buckwheat) and Triticum aestivum (spring wheat) from a Ca-bound form. The first experiment was based on a sand-culture system with either rock phosphate (RP) or CaHPO4 (CaHP) as the P source and nitrate or ammonium nitrate as nitrogen source. A highly calcareous soil was used in the second experiment. Buckwheat was shown to be highly efficient in taking up Ca-bound P compared to spring wheat. When plants were supplied with nitrate, the total P uptake by buckwheat from RP was nearly 10-fold higher than that of spring wheat (20.1 compared with 2.1 mg P pot−1). Changing nitrogen source from nitrate only to ammonium nitrate increased P uptake by spring wheat substantially, but not buckwheat. High P-uptake efficiency of buckwheat was also demonstrated using the field soil, but to a lesser extent, which may be related to the difference in Zn supply between sand culture and field soil. It is suggested that buckwheat may be included in intercropping or crop rotation systems to activate P sources in calcareous soils. The principal mechanism of P uptake efficiency of buckwheat may be its ability to acidify the rhizosphere; however, further study is needed to unravel the regulation of root excretion of H+ and its molecular basis in order to exploit buckwheat's genetic capability to utilise sparingly soluble P from soil.

Traits associated with improved P-uptake efficiency in CIMMYT's semidwarf spring bread wheat grown on an acid Andisol in Mexico.

Phosphorus deficiency is a major yield limiting constraint in wheat cultivation on acid soils. The plant factors that influence P uptake efficiency (PUPE) are mainly associated with root characteristics. This study was conducted to analyze the genotypic differences and relationships between PUPE, root length density (RLD), colonization by vesicular arbuscular and arbuscular mycorrhizal (V)AM fungi and root excretion of phosphatases in a P-deficient Andisol in the Central Mexican Highlands. Forty-two semidwarf spring-bread-wheat (Triticum aestivumL.) genotypes from CIMMYT were grown without (−P) and with P fertilization (+P), and subsequently in subsets of 30 and 22 genotypes in replicated field trials over 2 and 3 years, respectively. Acid phosphatase activity at the root surface (APASE) was analyzed in accompanying greenhouse experiments in nutrient solution. In this environment, PUPE contributed more than P utilization efficiency, in one experiment almost completely, to the variation of grain yield among genotypes. Late-flowering genotypes were higher yielding, because the postanthesis period of wheat was extended due to the cold weather at the end of the crop cycles, and postanthesis P uptake accounted for 40–45% of total P uptake. PUPE was positively correlated with the numbers of days to anthesis (at −P r=0.57 and at +P r=0.73). The RLD in the upper soil layer (0–20 cm) of the wheat germplasm tested ranged from 0.5 to 2.4 cm cm-3 at –P and 0.7 to 7.7 at +P. RLD was the most important root trait for improved P absorption, and it was positively genetically correlated with PUPE (at –P r=0.42 and at +P r=0.63) and the number of spikes m-2 (at –P r=0.58 and at +P r=0.36). RLD in the upper soil layer was more important with P fertilizer application. Without P fertilization, root proliferation in the deeper soil profile secured access to residual, native P in the deeper soil layer. (V)AM-colonisation and APASE were to a lesser degree correlated with PUPE. Among genoptypes, the level of (V)AM-colonisation ranged from 14 to 32% of the RLD in the upper soil layer, and APASE from 0.5 to 1.1 nmol s-1 plant-1 10-2.

Genetic variation in acquisition, and utilization of phosphorus from iron-bound phosphorus in pigeonpea

In earlier experiments it was observed that pigeonpea is one of the few crop species that can utilize fixed forms of soil-P, particularly iron-bound P (Fe-P). The present investigation was aimed at assessing the genotypic variation in P uptake from Fe-P in pigeonpea. Fifteen pigeonpea germplasm lines that comprised genotypes of different maturity groups and three wild relatives were grown in vermiculite supplied with 15 mg P either as Fe-P or Ca-P for 60 d. Significant genetic variation in P uptake from Fe-P was observed; also P-use efficiency varied substantially among the genotypes. Dry matter production was positively correlated with P uptake both under Fe-P and Ca-P treatments (r=0.78**; r=0.63*; n=15). There was no significant relation between P-use efficiency and dry matter production. Wild related species did not show higher P uptake from Fe-P than the cultivated pigeonpea. From Fe-P, the P uptake was only 36% of that from Ca-P. The best genotypes in the present study took up an amount of P equivalent to 55% of that from Ca-P. Significant differences were detected in P-uptake efficiency (μg P mg−1 root d.wt.) among the genotypes, but P uptake efficiency did not correlate with total P uptake. A positive correlation was found between P uptake and root dry matter production under Ca-P and Fe-P treatments (r=0.78**; r=0.63*; n=15). The differential P uptake by ICPL 88039, C 11, ICPL 88032, and ICPL 87 from Fe-P in the vermiculite study was confirmed in soil culture where the soil contained a small amount of available P, but substantial amounts of AI- and Fe-P. The results demonstrated the presence of a significant genotypic variation in P uptake from Fe-P in pigeonpea.

Exploitation of localized phosphorus-patches by common bean roots

Phosphorus (P) uptake from patches was investigated in high-P and low-P common bean (Phaseolus vulgaris L.) plants using a split-root system. A P-patch was developed by exposing a small sub-section of the root system to localized P enrichment. A soil-based media was used to provide realistically low, buffered levels of P. In addition, nutrient solution provided zero and 1 mM P to low-P and high-P plants, respectively. Overall, growth of low-P plants was approximately 40% that of high-P plants. Mycorrhizal infection by G. etunicatum had little detectable influence on plant growth. Root length exploring a P-patch was comparable for low-P and high-P plants, yet low-P plants allocated half as much root biomass and P to a P-patch compared to high-P plants. This was achieved by an increase in the investment in fine, terminal roots exploring a P-patch in low-P plants. P uptake per investment of dry weight in the P-patch was over 50% higher for high-P plants compared to low-P plants. The higher P-uptake efficiency in high-P plants was achieved despite the greater production of fine roots in low-P plants.