P-deficient Soil Research Articles

Depending on mother corm size, the removal of extra lateral buds regulates sprouting mechanism and improves phosphorus acquisition efficiency in saffron (Crocus sativus L.)

Low P solubility in arid and semi-arid regions dominated by alkaline or calcareous soils is known as a main limiting factor for sustainable saffron (Crocus sativus L.) production. Hence, it may be necessary to consider efficient approaches for improving P uptake mechanism. The effects of lateral buds removal and mother corm size on daughter corms behavior, flower yield and P acquisition efficiency (PAE) were studied in saffron grown in a P-deficient soil in a two-year field experiment during 2017–2018 and 2018–2019 growing seasons. The 16 main plots [lateral bud removal (no removing lateral buds as control, keeping apical bud + removing all lateral buds, keeping apical bud + 1 lateral bud, and keeping apical bud + 2 lateral buds) × mother corm size (4.1–6.0, 6.1–8.0, 8.1–10.0, and 10.1–12.0 g)] and 2 sub-plots (first and second sampling) were conducted based on a randomized complete block design arranged in factorial-split with 3 replicates. The maximum leaf area, flower number, and dried stigma yield were observed by keeping 2 lateral buds on mother corm. By contrast, the minimum values were obtained in control treatment. Furthermore, keeping 1 or 2 lateral buds alleviated the adverse effects of small-sized mother corm on leaf and flower related traits. Large-sized daughter corms (> 10.0 g) constituted 25.0, 22.5, and 22.1% of the total number of daughter corms, respectively, when 0, 1, and 2 lateral buds were kept on 10.1–12.0 g mother corms. The highest P concentration in large-sized daughter corms (3.72 g kg−1) and PAE (38.89%) were obtained by keeping 2 lateral buds on 10.1–12.0 g mother corms, while the lowest values (2.66 g kg−1 and 6.77%) were observed by planting 4.1–6.0 g untreated mother corms. It can be concluded that the sprouting mechanism in saffron is controlled by mother corm size. In sum, considering the cultivation of saffron in arid and semi-arid regions, selecting 10.1–12.0 g mother corms treated for keeping 2 lateral buds is recommended.

Interactive Effects of Plant Growth-Promoting Rhizobacteria and Phosphates Sources on Growth and Phosphorus Nutrition of Soybean under Moderate Drought

The growth of legume plants is usually improved by the rhizobacteria inoculation under low phosphorus (P) and alleviation of P nutrition plays important role in plant drought stress response. The aim of this study was to assess the comparative efficacy of two plant growth promoting rhizobacteria namely Burkholderia cepacia B36 and Enterobacter radicincitans D5/23T combined with two sources of phosphates in soybean (Glycine max L.) under low water supply. Plants were grown under P soluble versus insoluble P fertilization for comparing the effects of soybean inoculation on growth, uptake and use efficiency of phosphorus under moderate drought stress. At the beginning of flowering, half of plants was subjected to low water supply (35% water holding capacity, WHC) for 12 days while control plants were well watered - 70% WHC. The plants were harvested at the end of drought and physiological traits and P contents were analyzed. The inoculation treatments showed better plant growth and nutrient uptake when compared to uninoculated control. The application of the Burkholderia cepacia was more efficiently in terms plant growth than E. radicincitans especially under insoluble phosphates. Phosphorus concentrations of shoots and roots increased with both bacterial strains. The bacterial inoculation has much better stimulatory effect on nutrient uptake by soybean fertilized with insoluble phosphates. Study findings indicate that the combined application of PGPR (Burkholderia cepacia B36) and P amendments has the potential to improve P nutrition and growth of soybean cultivated on P-deficient soil under well-watered as well as moderate drought condition.
 
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 In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 3, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue.
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Phosphorus acquisition processes in the field: study of faba bean cultivated on calcareous soils in Algeria

ABSTRACTLittle is known about the occurrence of phosphorus (P) acquisition processes in the field, especially for faba bean (Vicia faba L.) in calcareous soils. We sampled soil, rhizosphere and plant materials in 12 calcareous field sites in Algeria and performed physicochemical analysis during two growing seasons. Both proton exudation and root exploration increased in P-deficient soils as compared to P-sufficient soils. Inhibition of nitrogen (N) fixation and rhizosphere alkalization were observed in N-rich soils. We also found that calcium (Ca) concentrations in both shoots and roots significantly increased with P-deficiency. The same trend, although less significant, was observed with respect to Ca uptake. These field observations suggested that acidifying roots acquired P from dissolving Ca-P minerals. The concomitant increase of the ratio Ca/P uptake should further enhance their dissolution. Other rhizosphere processes such as the mineralization of organic P should control P acquisition as alkalization occurred in the root zone in response to the inhibition of N fixation. In conclusion, P-acquisition processes in the field were consistent with previous findings made at the laboratory. In addition, the variety of faba bean cultivated by local farmers appeared relatively well adapted to field conditions thanks to the deployment of rhizosphere processes.

Variation in root morphology and P acquisition efficiency among Trifolium subterraneum genotypes

Trifolium subterraneum L. is widely grown in the phosphorus (P) deficient soils of southern Australia. However, this pasture legume has a high critical external P requirement and requires frequent applications of P fertiliser to achieve high productivity. Twenty-six genotypes of T. subterraneum were grown to determine: (i) differences in shoot growth and P acquisition under low-P supply; (ii) the root morphological traits important for P acquisition; and (iii) the feasibility of selection among genotypes for these root morphological traits. Micro-swards of each genotype were grown with a topsoil layer that was either moderately P-deficient or had P supplied in excess of the critical requirement for maximum yield; the subsoil layer was P-deficient. Yield and P content of shoots and roots were determined after 5 weeks’ growth, and root samples were assessed for diameter, length and root hair length. All genotypes were equally highly productive when excess P was supplied. However, relative shoot yield in the moderately P-deficient soil ranged from 38–71%. Total root length ranged from 63–129 m pot–1, and was correlated with total plant P uptake (R2 = 0.78, P < 0.001). Variation was also observed in average root diameter (0.29–0.36 mm) and root hair length (0.19–0.33 mm). These traits were combined with root length to calculate the total surface area of the root hair cylinder, which was also correlated with total plant P uptake (R2 = 0.69, P < 0.001). The results demonstrated that there was significant variation in P acquisition efficiency and shoot yield among genotypes of T. subterraneum when grown in P-deficient soil, and that root length was important for improved P uptake. The results indicate potential to identify superior genotypes that achieve improved P acquisition and higher shoot yields in low-P soil.

Cellulose and lignin regulate partitioning of soil phosphorus fractions and alkaline phosphomonoesterase encoding bacterial community in phosphorus-deficient soils

Crop straw retention is believed to effectively promote soil phosphorus (P) availability. However, little is known about how specific components of crop straw, such as cellulose and lignin, regulate soil P availability, which depends on several processes, including the reactions catalyzed by phosphomonoesterase activities. Of the genes encoding alkaline phosphomonoesterase, phoD are ubiquitous in soil. Here, we studied the effects of cellulose and lignin on soil P fractions and phoD-harboring bacterial community in P-deficient upland and paddy soils. In the upland soil, cellulose amendment significantly increased microbial P assimilation and decreased soil citrate-P and HCl-P fractions, suggesting that cellulose mediated the conversion of soil P fractions from the non-labile to the labile P pool (e.g., microbial P) via microbial enrichment. Lignin significantly increased soil Olsen-P content, but scarcely influenced P-related microbial parameters after incubation for 60 days. Therefore, lignin directly increased soil available P via competitive P adsorption by lignin functional groups, rather than by altering soil microbial processes. Compared to upland soil, a smaller effect of both cellulose and lignin on phoD gene abundance, alkaline phosphomonoesterase activity, and phoD-harboring bacterial community was observed in paddy soil, suggesting that the carbon inputs may be unable to promote organic P availability under oxygen-deficient conditions. Our results highlight the contrasting mechanisms of soil P availability regulation via cellulose or lignin in P-deficient soils.

Endophytic Bacillus strains enhance pearl millet growth and nutrient uptake under low-P.

Bacterial endophytes are considered to have a beneficial effect on host plants, improving their growth by different mechanisms. The objective of this study was to investigate the capacity of four endophytic Bacillus strains to solubilize iron phosphate (Fe-P), produce siderophores and indole-acetic acid (IAA) in vitro, and to evaluate their plant growth promotion ability in greenhouse conditions by inoculation into pearl millet cultivated in a P-deficient soils without P fertilization, with Araxá rock phosphate or soluble triple superphosphate. All strains solubilized Fe-P and three of them produced carboxylate-type siderophores and high levels of IAA in the presence of tryptophan. Positive effect of inoculation of some of these strains on shoot and root dry weight and the N P K content of plants cultivated in soil with no P fertilization might result from the synergistic combination of multiple plant growth promoting (PGP) traits. Specifically, while B1923 enhanced shoot and root dry weight and root N P content of plants cultivated with no P added, B2084 and B2088 strains showed positive performance on biomass production and accumulation of N P K in the shoot, indicating that they have higher potential to be microbial biofertilizer candidates for commercial applications in the absence of fertilization.

Correction to: Phosphorus addition enhances gross microbial N cycling in phosphorus-poor soils: a 15N study from two long-term fertilization experiments

The tight coupling between nitrogen (N) and phosphorus (P) suggests that P availability may affect soil microbial N dynamics in terrestrial ecosystems. However, how P addition affects the internal N transformations in P-deficient agricultural soil remains poorly understood. We hypothesized that an increase in gross microbial N rates in P-deficient soil should occur after long-term P inputs in agricultural soils. We thus conducted a 15N pool dilution experiment to quantify the gross microbial N transformation rates after long-term mineral fertilizer applications in an upland fluvo-aquic soil (from Fengqiu with pH 8.55) and upland red soil (from Qiyang with pH 5.49) in China. We found that P addition significantly enhanced the gross N mineralization and immobilization rates when N and K were also applied, probably due to the increased soil total C and N concentrations at both soils. Also, gross nitrification rate was stimulated by P addition, perhaps because of enhanced gross N mineralization rates and associated NH4+ substrate availability. Our results showed that long-term P addition may stimulate soil gross N dynamics and hence increase overall N availability for crops in P-deficient agricultural soils.

Phosphorus dynamics in a tropical forest soil restored after strip mining

Background and aimsWe hypothesized that successful early ecosystem and soil development in these P-deficient soil materials will initially depend on effective re-establishment of P storage and cycling through organic matter. This hypothesis was tested in a 26-year chronosequence of seven lightly fertilized, oxidic soil materials restored to eucalypt forest communities after bauxite mining.MethodsTotal P (Pt) status, Hedley P fractions and partial chemical speciation (NaOH-EDTA extraction and analysed using solution 31P NMR spectroscopy) were determined in the restored soils.ResultsConcentrations of Pt and most Hedley fractions changed with restoration period, declined with depth and were strongly positively correlated with C and N concentrations. Biological P dominated the Labile and Intermediate P fractions while Long-term P was dominantly inorganic. Organic P concentrations in NaOH-EDTA extracts and their chemical natures were similar in restored and unburned native forest sites. Phosphomonoesters were the dominant class of organic P.ConclusionsSurprisingly rapid P accretion and fractional changes occurred over 26 years, largely in the surface soils and closely associated with organic matter status. Alkaline hydrolysis products of phosphodiesters and pyrophosphate indicated the importance of microbial P cycling. The important consequences for long-term ecosystem development and biological diversity require further study.

Comparison of the nutrient resorption stoichiometry of Quercus variabilis Blume growing in two sites contrasting in soil phosphorus content

Foliar phosphorus (P) resorption in Quercus variabilis Blume was significantly lower at a P-rich than at a P-deficient site. Moreover, P resorption strongly decreased, and nitrogen:phosphorus and carbon:phosphorus resorption ratios increased with soil P content. This demonstrates a strong link between foliar P resorption and P content in soils, and emphasizes the importance of P resorption in leaves of trees growing in soils with contrasted P content. Subtropical ecosystems are generally characterized by P-deficient soils. However, P-rich soils develop in phosphate rock areas. We compared the patterns of nutrient resorption, in terms of ecological stoichiometry, for two sites naturally varying in soil P content. The resorption efficiency (percentage of a nutrient recovered from senescing leaves) and proficiency (level to which nutrient concentration is reduced in senesced leaves) of 12 elements were determined in two oak (Q. variabilis) populations growing at a P-rich or a P-deficient site in subtropical China. P resorption efficiency dominated the intraspecific variation in nutrient resorption between the two sites. Q. variabilis exhibited a low P resorption at the P-rich site and a high P resorption at the P-deficient site. Both P resorption efficiency and proficiency strongly decreased with soil P content only and were positively related to the N:P and C:P ratios in green and senesced leaves. Moreover, resorption efficiency ratios of both N:P and C:P were positively associated with soil P. These results revealed a strong link between P resorption and P stoichiometry in response to a P deficiency in the soil, and a single- and limiting-element control pattern of P resorption. Hence, these results provide new insights into the role of P resorption in plant adaptations to geologic variations of P in the subtropics.

An evaluation of phosphorus uptake in Sesbania cannabina when ferric phosphate is applied in the presence of phosphate-solubilizing rhizobia

Deficient available phosphorus (P) in soils can majorly limit crop production. Furthermore, nodule formation in legumes is inhibited in P-deficient soil. Phosphate-solubilizing rhizobia are supposed to improve the plant P uptake even in insoluble P accumulated soil. We investigated the utilization of insoluble ferric phosphate, which is generally less available for agricultural crops, by Sesbania cannabina inoculated with phosphate-solubilizing rhizobia. Our evaluation of the P-solubilizing capacity showed that P was mineralized from ferric phosphate in inoculated rhizobia. In the soluble P treatment, nodule dry weight was significantly correlated with shoot dry weight and P content. Nodule dry weight and nitrogenase activity in S. cannabina supplied with ferric phosphate were significantly higher than those in the soluble P treatment. But, these increases were not necessarily effective on P status in the plants supplied with ferric phosphate.

Modelling varietal differences in response to phosphorus in West African sorghum

In West Africa’s highly weathered soils, plant-available soil-P levels determine sorghum performance and yield to a far greater extent than projected variability in climate. Despite local landrace varieties having excellent adaptation to the environment and a relatively stable yield, sorghum grain yield remains quite low, averaging less than 1 t ha−1. Low P availability in West African soils has significant effects on crop development and growth with potential grain yield losses of more than 50%. Use of mechanistic models, which integrate physiological processes, could assist with understanding the differences in P-uptake among varieties and guide effective P management. Yet only few crop models include a soil-plant P model for simulating crop yield response to P management. A generic soil-plant P module was developed for crop models in the Cropping System Model (CSM) of the Decision Support System for Agrotechnology Transfer (DSSAT) but the module was adapted and tested only on two crops, groundnut and maize. The aim of the study was to adapt the soil-plant P module for sorghum and perform initial testing on highly weathered soils in West Africa. Data used in adapting and testing the soil-plant P model for sorghum consisted of in-season P concentrations and dry weights of stems, leaves and grain from four sorghum varieties covering a range of maturities and photoperiod sensitivities and grown in high-P and P-deficient soils at ICRISAT-Mali. Results showed that the coupled CERES-Sorghum − P module reasonably reproduced the vegetative and grain yield reductions experienced in the field experiments with an average RMSE of 1561 and 909 kg ha−1 under high P conditions and 1168 and 466 kg ha−1 under low P conditions, respectively. The simulations are in most cases within the observation error. We also confirmed that contrasting variety types differ in their P-uptake dynamics relative to above-ground growth change over time, and hence respond differently to available P.

Tailoring hydroxyapatite nanoparticles to increase their efficiency as phosphorus fertilisers in soils

Hydroxyapatite nanoparticles (HA-NPs) have been proposed as a novel phosphorus (P) fertiliser that could potentially provide increased efficiency through controlled release. In the present study, three types of HA-NPs were synthesised with differences in surface charge and hydrodynamic sizes before being incubated in two P-deficient soils (an Ultisol and a Vertisol) in the laboratory for up to 240 d. The three types of HA-NPs had surface charge values of +21 (±4.3), 0 (±3.5) and −12 (±2.7) mV in a neutral medium (pH 7). In the Ultisol (pH 4.7), the addition of HA-NPs resulted in a smaller initial increase in P availability than triple superphosphate (TSP) due to their lower solubility. However, P availability in the TSP treatment decreased over time due to adsorption of P to the soil constituents, with a concomitant increase in the NaOH-extractable P fraction. In contrast, the release of P from the HA-NPs remained relatively constant over the entire incubation period. After 45 d, the soils amended with negatively charged HA-NPs had higher levels of available P when estimated using diffusive gradients in thin films (DGT-P) compared to both the neutral and the positively charged HA-NPs. In the Vertisol (pH 8.2), although the addition of TSP increased P availability markedly, amendment with the three HA-NPs did not increase P availability due to the low solubility of hydroxyapatite at this high pH. Indeed, for the Vertisol, most of the P added as HA-NPs remained in the Ca-P fraction. Our results show that for the acidic Ultisol, HA-NPs with altered surface charges are potentially a useful form of slow release P.

Does P-deficiency fertilization alter chemical compositions of fulvic acids? Insights from long-term field studies on two contrasting soils: A Fluvisol and an Anthrosol

Structural changes in fulvic acid (FA) in response to fertilization strategies, especially P-deficiency fertilization, have critical implications for soil carbon dynamics. This study examined how long-term fertilization influenced chemical compositions of soil FA and its humification degree. Advanced solid-state 13C nuclear magnetic resonance techniques were used to evaluate structural changes of FAs from two soils (a Fluvisol and an Anthrosol) under four fertilizer treatments: organic fertilizer combined with or without NPK fertilizer (OF and NPKOF), deficient in phosphorus only (NK) and Control. The greater aromaticity, hydrophobicity and alkyl/O-alkyl (A/O-A) ratios of FAs were observed in the Anthrosol than in the Fluvisol. The Anthrosol FAs contained more alkyl and aromatic C but fewer O-alkyls (mostly being protonated) than did the Fluvisol FAs. Both FAs comprised some nonprotonated aromatics, which decreased with applications of organic and NK fertilizers. This trend was less obvious for the Anthrosol than for the Fluvisol. Organic fertilizer treatments (OF and NPKOF) in the Fluvisol increased the A/O-A ratio and aromaticity compared with P-deficient soils (NK and Control), indicating organic fertilization promoted the humification degree of its FA. The NK treatment in the Fluvisol increased H/C ratio of FA. Compared with the Fluvisol FAs, the Anthrosol FAs displayed similar chemical natures, implying their formation followed similar processes with a similar humification degree. The findings suggest that long-term fertilization differently influenced the FAs from the Fluvisol and Anthrosol. Clearly, the Anthrosol FAs shared more common features among the treatments compared with the Fluvisol FAs, whereas P-deficiency rendered the Fluvisol FAs simpler.

Phosphorus-acquisition characteristics and rhizosphere properties of wild barley in relation to genotypic differences as dependent on soil phosphorus availability

This study focused on P acquisition mechanisms of Hordeum spontaneum from P-impoverished soil by measuring plant growth, P acquisition and rhizosphere properties. Two P-efficient genotypes (IS-22-30 and IS-22-25) and a P-inefficient genotype (IS-07-07) were subjected to a P supply of 0, 30 mg kg−1 (deficient P) and 60 mg kg−1 (sufficient P) in a rhizobag experiment. After 60 days, biomass, P concentration, and P uptake were analyzed. Changes in pH, P fractions and acid phosphatase activity in soil at different distances from the roots were determined, using a slicing technique. P-efficient genotypes showed greater biomass and plant P content, but lower plant P concentration than the P-inefficient genotype. The average seed P content was 113 and 176 μg P per seed of P-efficient genotypes and P-inefficient genotype, respectively. P-efficient genotypes showed P uptake of 3.0 and 7.9 mg pot−1 at 0 and 30 mg P kg−1; while that of P-inefficient genotype was 1.0 and 5.3 mg pot−1, respectively. Acid phosphatase activity was significantly enhanced in the soil-root interface and P-efficient genotypes demonstrated 54% greater activity of rhizosphere acid phosphatase than the P-inefficient genotype. Rhizosphere P fractions showed that P utilized by the two genotypes mainly came from H2O-Pi, NaHCO3-Pi, and NaOH-Pi, while the P-efficient genotypes markedly depleted NaHCO3-Po, NaOH-Po and HCl-Pi, and the depletion zone extended to 4 mm under P deficiency. These results indicate the potential to sustain more growth and greater P acquisition by P-efficient genotypes of wild barley from P-deficient soil through changes of rhizosphere P fractions and enhancing rhizosphere acid phosphatase activity.

A Single Application of Phosphorus at Planting Improves Long-term Asparagus Root Growth and Yield

ABSTRACTMature Asparagus (Asparagus officinalis L) plantings are only marginally responsive to added phosphorus (P). There is little information addressing P needs of new asparagus plantings. In 1999, a trial was established in a P-deficient soil to assess effects of increasing P levels at planting on asparagus growth and productivity. Prior to planting, 0 to 450 kg·ha−1 of P was blended in the planting furrow. Fleshy root growth and carbohydrate content were measured periodically and fern growth was evaluated during the summer and autumn of each year. Spears were harvested beginning in 2001. Increasing soil P levels had a variable effect on asparagus spear yield during limited harvests of 2001 and 2002. By full harvest in 2003–2005, spear yield increased linearly with increasing P. Yield increase was associated with a linear increase in root biomass but not root carbohydrate content. A single early application of P can improve asparagus productivity.

Biochar Functions as Phosphorous Fertilizers in an Alkaline Alluvial Soil

ABSTRACTWith the depletion of global phosphorous (P) reserves, finding alternatives to P fertilizers has been gaining more and more attention. This study was conducted to identify whether biochar application could improve P availability in a P-deficient alkaline alluvial soil. Unground biochar contained a high level of 692 mg kg−1 extractable P, over 100 times more than that in the soil. Extractable P content increased significantly with the decrease of biochar particle size. There was a significant positive correlation between soil available P content and biochar application rates. The pot experiment showed that biochar application significantly increased the soil available P content before sowing, and significantly improved the aboveground biomass of soybean and promoted P uptake at harvest. Biochar, as containing abundant extractable P, could go partly on substituting mineral P fertilizers as well as promote plant growth and reduce P fertilizer application in agriculture.

Characterization of phosphate-solubilizing bacteria exhibiting the potential for growth promotion and phosphorus nutrition improvement in maize (Zea mays L.) in calcareous soils of Sinaloa, Mexico

Greenhouse bioassays were used to examine the ability of selected strains of the rhizobacteria Sinorhizobium meliloti, Bacillus flexus and B. megaterium to solubilize phosphorus (P) and to affect growth promotion and phosphorus nutrition in maize. These bacterial strains were found to decrease the pH and solubilize some forms of insoluble P, such as tricalcium phosphate and hydroxyapatite, as well as to exhibit acid and alkaline phosphatase enzymatic activities in culture medium, properties that are possibly involved in P solubilization. Inoculation of the strains separately and as a consortium of the three bacteria (S. meliloti, B. flexus and B. megaterium) in P-deficient soil (4.33 w/v P) fertilized without P improved plant height, shoot and root dry weight, as well as P nutrition in the maize plants. Use of the B. flexus and B. megaterium strains separately and in a consortium positively affected several growth parameters and P nutrition in plants supplemented with insoluble P. No effect was observed when pots in which the seedlings were growing were supplied with soluble fertilizer. A second assay using a P-deficient soil (6.64 w/v P) showed that inoculation with the consortium of B. flexus and B. megaterium significantly increased growth and total P content in maize plants. A dose–response P fertilization experiment using sterile P-deficient soil led us to conclude that inoculation to soil of the mixture of B. flexus and B. megaterium may improve P nutrition and growth to a level previously attained by the addition of soluble P-fertilizer at 40 w/v P. A non-sterile experiment showed a beneficial response with B. megaterium but not with B. flexus. We propose utilizing these bacteria in P-deficient alkaline soils in future field trials in order to evaluate their potential as biofertilizers.

Nutrient Composition and Distance from Point Placement to the Plant Affect Rice Growth

Point placement of urea is an efficient technology to improve urea use efficiency in transplanted rice (Oryza sativa L.), but it is largely unknown how nutrient composition in the point placement and the distance from placement site to the plant influence rice root distribution and growth, nutrient uptake, and rice grain yield. A controlled greenhouse experiment was conducted using both N- and P-deficient soil with point placement of N only or N and P together (N + P) at a distance close to or far from the plant, in comparison to an N-spilt application and a no-N control. Both nutrient composition and distance significantly affected rice root growth. Compared with the N point placement, the N + P point placement led to smaller root length and mass densities, higher specific root length (SRL) around the placement site, smaller root system, higher straw mass and grain yield, and higher N and P uptake. The difference between the N + P and N point placements was greater when close to the plant than when far from the plant. It is suggested that higher SRL around the placement site is essential for improving nutrient uptake and rice grain yield, and simultaneous point placement of N and P has a synergistic effect on rice growth.

Uptake and utilization of applied phosphorus in oilseed rape (Brassica napus L. cv. Hayola) plants at vegetative and reproductive stages: Comparison of root with foliar phosphorus application

ABSTRACTIn order to compare plants’ response to phosphorus (P) application through roots and leaves, oilseed rape (Brassica napus L. cv. Hayola) plants were cultivated until vegetative or reproductive stages and were pretreated with an adequate (+P) or low (−P) supply of P. Thereafter, these plants were treated with 0.3 mM P as sodium dihydrogen phosphate (NaH2PO4) either through roots (root application, RA) or leaves (leaf application, LA). Shoot biomass was observed to be suppressed under −P conditions at both stages, whereas root growth was comparatively improved in −P plants at the vegetative stage but not at the reproductive stage. Both RA and LA were able to compensate for the growth of vegetative shoot and roots at both stages; however, LA reduced P and dry matter partitioning into the fruits. At the vegetative stage, recovery of applied P was similar between RA and LA treatments, and was extensive in −P plants compared with the +P ones. At the reproductive stage, in contrast, significantly lower recovery of P was observed likely due to the lower capacity of leaves for P absorption and/or their lower re-translocation ability through the phloem. Data of P utilization efficiency showed that −P plants, at both vegetative and reproductive stages, efficiently use leaf-applied P for biomass production when compared with the +P plants. Activity of acid phosphatase was sharply inhibited by RA in −P plants, whereas it was preferably increased by LA in both +P and −P plants. Results indicated that under P-deficiency conditions, plants had higher ability to utilize foliar-applied P, and in contrast to RA, LA may enable plants for a continuous higher capacity of P uptake from P-deficient soil; however, RA was superior to LA in terms of fruit growth.

Elemental stoichiometry and compositions of weevil larvae and two acorn hosts under natural phosphorus variation

To understand how different trophic organisms in a parasite food chain adapt to the differences in soil nutrient conditions, we investigated stoichiometric variation and homeostasis of multiple elements in two acorn trees, Quercus variabilis and Quercus acutissima, and their parasite weevil larvae (Curculio davidi Fairmaire) at phosphorus (P)-deficient and P-rich sites in subtropical China where P-rich ores are scattered among dominant P-deficient soils. Results showed that elemental stoichiometry and compositions of both acorns and weevil larvae differed significantly between P-deficient and P-rich sites (p < 0.05), with the largest contribution of acorn and weevil larva P in distinguishing the stoichiometric compositions between the two site types. The two acorn species were statistically separated by their acorn elemental stoichiometry and compositions (p < 0.05), but no difference was observed on weevil larvae between the two acorn species. P was one of the few elements that were non strict homeostasis in both acorns and weevil larvae. These findings highlight the importance of both environmental influence in elemental stoichiometry and composition and physiological regulations of nutritional needs in organisms and provide possible stoichiometric responses of both plants and animals to P loading, a worldwide issue from excess release of P into the environment.