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Abstract Background Fungi and bacteria coexist in a wide variety of environments, and their interactions are now recognized as the norm in most agroecosystems. These microbial communities harbor keystone taxa, which facilitate connectivity between fungal and bacterial communities, influencing their composition and functions. The roots of most plants are associated with arbuscular mycorrhizal (AM) fungi, which develop dense networks of hyphae in the soil. The surface of these hyphae (called the hyphosphere) is the region where multiple interactions with microbial communities can occur, e.g., exchanging or responding to each other’s metabolites. However, the presence and importance of keystone taxa in the AM fungal hyphosphere remain largely unknown. Results Here, we used in vitro and pot cultivation systems of AM fungi to investigate whether certain keystone bacteria were able to shape the microbial communities growing in the hyphosphere and potentially improved the fitness of the AM fungal host. Based on various AM fungi, soil leachates, and synthetic microbial communities, we found that under organic phosphorus (P) conditions, AM fungi could selectively recruit bacteria that enhanced their P nutrition and competed with less P-mobilizing bacteria. Specifically, we observed a privileged interaction between the isolate Streptomyces sp. D1 and AM fungi of the genus Rhizophagus, where (1) the carbon compounds exuded by the fungus were acquired by the bacterium which could mineralize organic P and (2) the in vitro culturable bacterial community residing on the surface of hyphae was in part regulated by Streptomyces sp. D1, primarily by inhibiting the bacteria with weak P-mineralizing ability, thereby enhancing AM fungi to acquire P. Conclusions This work highlights the multi-functionality of the keystone bacteria Streptomyces sp. D1 in fungal-bacteria and bacterial-bacterial interactions at the hyphal surface of AM fungi. Video Abstract

Background: Fungi and bacteria coexist in a wide variety of environments, and their interactions are now recognized as the norm in most agroecosystems. These microbial communities harbor keystone taxa, which facilitate connectivity between fungal and bacterial communities, influencing their composition and functions. The roots of most plants are associated with arbuscular mycorrhizal (AM) fungi, which develop dense networks of hyphae in the soil. The surface of these hyphae (called the hyphosphere) is the region where multiple interactions with microbial communities can occur, e.g., exchanging or responding to each other's metabolites. However, the presence and importance of keystone taxa in the AM fungal hyphosphere remain largely unknown. Results: Here, we used in vitro and pot cultivation systems of AM fungi to investigate whether certain keystone bacteria were able to shape the microbial communities growing in the hyphosphere and potentially improved the fitness of the AM fungal host. Based on various AM fungi, soil leachates, and synthetic microbial communities, we found that under organic phosphorus (P) conditions, AM fungi could selectively recruit bacteria that enhanced their P nutrition and competed with less P-mobilizing bacteria. Specifically, we observed a privileged interaction between the isolate Streptomyces sp. D1 and AM fungi of the genus Rhizophagus, where (1) the carbon compounds exuded by the fungus were acquired by the bacterium which could mineralize organic P and (2) the in vitro culturable bacterial community residing on the surface of hyphae was in part regulated by Streptomyces sp. D1, primarily by inhibiting the bacteria with weak P-mineralizing ability, thereby enhancing AM fungi to acquire P. Conclusions: This work highlights the multi-functionality of the keystone bacteria Streptomyces sp. D1 in fungal-bacteria and bacterial-bacterial interactions at the hyphal surface of AM fungi. 3XiVYVBxkNucerLC-WX6of Video Abstract [ABSTRACT FROM AUTHOR]

Tree species establish mycorrhizal associations with both ectomycorrhizal (EM) and arbuscular mycorrhizal fungi (AM), which play crucial roles in facilitating plant phosphorus (P) acquisition. However, little attention has been given to the effects of EM and AM species on soil P dynamics and the underlying mechanisms in subtropical forests, where P availability is typically low. To address this knowledge gap, we selected two EM species (Pinus massoniana - PM and Castanopsis carlesii - CC) and two AM species (Cunninghamia lanceolata - Chinese fir, CF and Michelia macclurei - MM) in a common garden established in 2012 in subtropical China. We investigated soil properties (e.g., pH, soil organic carbon, total nitrogen, and dissolved organic nitrogen), soil P fractions, phospholipid fatty acids (PLFAs), enzyme activities, foliar manganese (Mn) concentration, and foliar nutrients and stoichiometry. Our findings revealed that soils hosting EM species had higher levels of resin P, NaHCO3-Pi, extractable Po, total P, and a greater percentage of extractable Po to total P compared to soils with AM species. These results indicate that EM species enhance soil P availability and organic P accumulation in contrast to AM species. Moreover, EM species exhibited higher P return to soil (indicated by higher foliar P concentrations) when compared to AM species, which partly explains higher P accumulation in soils with EM species. Additionally, resin P showed a positive correlation with acid phosphatase (ACP) activity, whereas no correlation was found with foliar Mn concentration, which serves as a proxy for the mobilization of sorbed soil P. Such findings indicate that organic P mineralization has a more substantial impact than inorganic P desorption in influencing P availability in soils hosting both EM and AM species. In summary, our study contributes to a more comprehensive understanding of the effects of mycorrhizal associations on soil P accumulation in subtropical forests and provide valuable insights into plant-soil interactions and their role in P cycling in regions with limited P availability. [ABSTRACT FROM AUTHOR]

Long-term application of dairy liquid manure (DLM) can modify soil phosphorus (P) dynamics. P fractionation allows the identification of organic and inorganic P and its lability via procedures of lesser and greater power extraction. The aim was to evaluate the effect of successive DLM applications (10 years) in no-tillage on soil P fractions. The experiment was carried out in an Oxisol with a sandy clay loam texture. Treatments consisted of three DLM doses (60, 120, and 180 m3 ha−1 year−1) and the control (unmanured) (0 m3 ha−1 year−1) randomized in a complete block design with four replicates. The soil was sampled at three depths (0–0.05; 0.05–0.10, and 0.10–0.15 m), and sequential extractions were performed for each depth. DLM increased soil P concentrations in all fractions, mainly in the 0–0.05 m depth resulting in the following proportions of P (average of all DLM doses in 0–0.05 m depth): labile (29%), moderately labile (38%), low lability (17%), and residual (16%). In the unmanured treatment, the proportion was labile (18%), moderately labile (39%), low lability (22%), and residual (21%). DLM application resulted in a higher proportion of organic and inorganic labile P (water, resin, and NaHCO3) indicating a greater plant availability but also a P water pollution risk by surface runoff. [ABSTRACT FROM AUTHOR]

Phosphorus (P) unavailability in agricultural soils is a primary cause of the poor development and yield of field crops in arid and semiarid regions. The primary goal of this research project was to investigate the influence of integrated management of beneficial microbes or biofertilizers (BF), organic P-fertilizers, and inorganic P-fertilizers on wheat productivity in a wheat–maize cropping system. Field experiments were carried out during the two consecutive seasons of 2020/2021 (Y1) and 2021/2022 (Y2) according to the two-factorial randomized complete block design with three replications. Factor one consisted of twenty-one treatments of organic and inorganic P-fertilizer combinations, while factor two consisted of two different BF (PSB and Bioaab). One overall control where no P or BF was applied was also included in each replication for comparison. The experiment consisted of six treatments of sole P sources (sheep manure (SM), cattle manure (CM), legume residues (LR), non-legume residues (NLR), single super phosphate (SSP) and rock phosphate (RP)), each applied at a rate of 90 kg P ha−1. Different combinations of organic and inorganic P sources (giving 15 treatments) were applied at a rate of 50% P from each source (i.e., 45 kg P ha−1 applied from different sources in combination). The results revealed that the combined application of SSP+SM produced a significantly higher number of grains spike−1 (23.9%), spikes m−2 (4.5%), and grain yield (40.9%) over the control. Application of PSB produced the maximum number of grains spike−1 (23.9%), spikes m−2 (4.5%), thousand-grain weight (8.3%), grain yield (40.9%), and biological yield (17%) in the wheat crop as compared to Bioaab. It was concluded from the two-year study that integrated use of organic P-fertilizers (animal manures) plus inorganic P-fertilizer (SSP) along with PSB ranked first in terms of higher wheat productivity in a wheat–maize cropping system. [ABSTRACT FROM AUTHOR]

Phosphate (Pi) deficiency leads to the induction of purple acid phosphatases (PAPs) in plants, which dephosphorylate organic phosphorus (P) complexes in the rhizosphere and intracellular compartments to release Pi. In this study, we demonstrate that OsPAP3b belongs to group III low-molecular weight PAP and is low Pi-responsive, preferentially in roots. The expression of OsPAP3b is negatively regulated with Pi resupply. Interestingly, OsPAP3b was found to be dual localized to the nucleus and secretome. Furthermore, OsPAP3b is transcriptionally regulated by OsPHR2 as substantiated by DNA–protein binding assay. Through in vitro biochemical assays, we further demonstrate that OsPAP3b is a functional acid phosphatase (APase) with broad substrate specificity. The overexpression (OE) of OsPAP3b in rice led to increased secreted APase activity and improved mineralization of organic P sources, which resulted in better growth of transgenics compared to the wild type when grown on organic P as an exogenous P substrate. Under Pi deprivation, OsPAP3b knock-down and knock-out lines showed no significant changes in total P content and dry biomass. However, the expression of other phosphate starvation–induced genes and the levels of metabolites were found to be altered in the OE and knock-down lines. In addition, in vitro pull-down assay revealed multiple putative interacting proteins of OsPAP3b. Our data collectively suggest that OsPAP3b can aid in organic P utilization in rice. The APase isoform behavior and nuclear localization indicate its additional role, possibly in stress signaling. Considering its important roles, OsPAP3b could be a potential target for improving low Pi adaptation in rice. [ABSTRACT FROM AUTHOR]

Soil aggregation in forest ecosystem is considered as a significant physical process mainly influenced by manure, fertilizers or combination. This aggregation may directly alter the soil nutrient and their fractions in soil. So, soil samples were collected from two types of forests i.e. Natural Korean pine forests (NKPF) and Korean pine plantation (KPP) in order to know the quantities of organic and inorganic Phosphorus (P) amounts in different aggregate sizes viz. >5 mm, 2–5 mm, 0.25–2 mm, 5 mm) and decreased with the decreasing aggregate size, while other variables, i.e., NaOH-Pi, NaHCO3-Po, pH and T-N were not affected in aggregate size. H2O-Pi (48 ppm), NaHCO3-Pi (68 ppm), NaHCO3-Po (80 ppm), NaOH-Po (623 ppm), HCL-Po (67 ppm), SOC (20.36 ± 1.6) was estimated in medium fertilizer treatment. PCA analysis showed that spread/variance of data points on F1 (62.90%) is more than spread/variance of data points on F2 (57.74%) in NKPF and KPP, respectively, while correlation matrix showed high correlation between H2O-Pi and NaOH-Pi (0.63) and H2O-Pi and NaHCO3-Pi (0.63) while a strong negative correlation was present between Res-Pi and Po (−0.61). Moreover, litter inputs increased the organic-P fractions in soil particularly at medium treatment.

Chara is usually found in hard and alkaline waters with low level of phosphorus (P) concentration. Calcite encrustation with P co-precipitation is very important for the growth of Chara and the maintenance of a low nutrient state in aquatic ecosystems. However, the effects and mechanisms of elevated P content in water on the growth, uptake and allocation of P in Chara are not well understood. This study performed an experiment to clarify how Chara vulgaris Linn, a common and widely distributed macroalga, allocated the P it uptake at different P availability. The results indicated that the growth rate of C. vulgaris in low P treatments (LP, less than 6 μg P /L) was 0.8 times higher than that in high P treatments (HP, more than 100 μg P /L), and the growth rate was significantly increased when C. vulgaris were transferred from the water with high P content to water with low P content, indicating that high P contents in water inhibited the growth of C. vulgaris. The increase of P content in water resulted in a fourfold increase in inorganic P (IP) content, while only 0.2-fold increase in organic P (OP) content, making the stoichiometric homeostasis index (1/H) of IP 7.9 times that of OP. More than 70% of the total P (TP) accumulated in Chara in LP was used for biomass growth, while more than 60% of the TP in C. vulgaris in HP was precipitated into calcite encrustation. This study highlighted that C. vulgaris had high growth rate under low P environment, and the inhibiting effect of high P to C. vulgaris was reversible, which may be a special P competition mechanism for this species in low P water. However, in high P condition, the Ca-P co-precipitation may limit the apparent P availability and be expressed as an inhibition of growth. [ABSTRACT FROM AUTHOR]

The sources of P and N in water-carrying lakes include exogenous input and endogenous release. However, the influence of pollution from different sources on the dynamic distribution of N and P at the sediment-water interface in water-carrying lakes remains unclear. The objectives of this study were to investigate the differences in dynamic distribution characteristics of P compounds and N elements in Lake Jiaogang, a major water-carrying lake in eastern China. Four functional regions with different types of pollutant sources and different kinds of aquatic plants were selected to study the distribution of total P (TP), inorganic P, organic P, ammonium (NH4+–N), and nitrate (NO3−–N). The results revealed that regions with internal-source pollutants contained the highest concentration of TP, Ca–P, and Fe–P with high concentrations. L–P, Al–P, mostly organic P, and soluble reactive phosphorous (SRP), the region with internal-source pollutants were lower than that with the imported-source pollutant. The concentration of dissolved NH4+–N showed high in regions with imported-source pollutants, however, in regions with internal-source pollutants, the dissolved NO3−–N was with the highest concentration. Overall, P from upstream was still dominant in the sediments despite uptake by the aquatic plants. SRP showed high concentration in regions with imported-source pollutants due to the imported pollution and the improved bioavailability by plant root exudates. Feces and feed residues from aquatic livestock breeding resulted in the highest concentration of TN, NH4+–N, and dissolved NO3−–N in the sediments of the region with internal-source pollutants. High concentrations of dissolved NH4+–N were due to the input of N from imported source pollutants. This study provides insights into the contributions of P and N to the eutrophication of the water-carrying lake. [ABSTRACT FROM AUTHOR]

Phosphate solubilizing microbes (PSM) can improve soil P availability by P dissolution. These microbes can make substances that regulate plant growth, which promotes plant growth. The present study aimed to characterize PSM and determine how PSM application affected P solubilization, soil phosphatase activity, and upland rice yield. The greenhouse experiment used a factorial randomized block design (RBD) with two factors and three replications. The first factor was PSM isolates, which came in four different forms: without microbes, with microbes (Burkholderia sp.), with fungus (Penicillium sp.), and with a combination of microbes (Burkholderia sp. and Penicillium sp.). The PSM isolates were characterized to analyze the production of organic acids, phosphatase enzymes, and phytohormones. The second factor was the superphosphate fertilizer dose, which has four levels: 0, 50, 75, and 100 kg P ha−1. According to the PSM characterization, it produced organic acids such as lactate acid, oxalate acid, citric acid, and acetate acid, as well as phytohormones (IAA) and the enzyme phosphatase. The pot experiment results show that the PSM inoculation raised the available P and soil phosphatase, P content of the plant, decreased soil organic P, and increased upland rice production. For improving available P, phosphatase activity, P content of the plant, and upland rice yields, mixed inoculants of phosphate-solubilizing bacteria and fungi performed better. The availability of soil P, the activity of the enzyme phosphatase, and the upland rice yields were all improved by applying P fertilizer at 75 kg P ha−1. This study showed that PSM as a biofertilizer reduced the dosage of inorganic fertilizers by up to 25%.

Processes governing soil organic matter (SOM) decomposition and mineralization are important for soil fertility and ecosystem sustainability. However, in the sub-Saharan region, limited work has been conducted on SOM dynamics; therefore, there was an imperative need for this study. The objective of this study was to determine the phosphorus (P) and nitrogen (N) dynamics in soil under different tillage and fertilizer management practices. The field trial was arranged as a randomized split plot design, with tillage forming the whole plot and the fertilizer application rate being the sub-plot. The tillage techniques were no-till (NT), annual tillage (CT-ANNUAL) and conventional tillage every fifth season (CT-Y5), whereby NT was practiced for four consecutive seasons, and in the fifth season, conventional tillage was employed. For all these tillage techniques, urea fertilizer was applied in amounts of 60, 120 and 240 kg N ha−1 with a control for each tillage treatment. Ammonium and nitrate levels were determined calorimetrically. Sulfuric acid, at 1 M, along with 0.057 M ascorbic acid and molybdate reagent were used to extract the organic P from the soil and extractable P. The total N, ammonium, total P, organic P and extractable P in the surface soil under NT were higher (p < 0.05) compared to the values of both CT-Y5 and CT-ANNUAL. The high levels of total N, N mineralization, total P, organic P and extractable P under NT, compared to CT-Y5 and CT-ANNUAL, at the depth of 0–10 cm may be attributed to the accumulation of crop residues on the surface and less soil disturbance. Furthermore, nitrate was found in higher (p < 0.05) concentrations under CT-ANNUAL compared to CT-Y5 at all the application rates and depths. The ploughing of soil under CT-ANNUAL improves the aeration, which accelerates the decomposition of organic material and mineralization of organic N and P into soluble forms. No-till, at 60 kg N ha−1 and a 0–10 cm soil depth, had optimum total N, nitrate, ammonium, total P and organic P values, thus showing its salient impact on the maintenance of soil fertility. However, the conclusion drawn from this study is that CT-Y5, due to its average N and P pools, can be recommended to under-resourced farmers in sub-Saharan preferentially over both NT and CT-ANNUAL, because it does not require advanced technology and equipment and it sustains an average soil fertility. [ABSTRACT FROM AUTHOR]

Over the past decade, scientific studies have increasingly concentrated on the effects of global phosphorus (P) scarcity on food security. A comprehensive strategy that considers demand reduction and recycling possibilities is needed to address the global P scarcity. Reduced tillage along with crop residue retention could decrease fixation of P in soil, improve labile P content and enhance organic-P (Po) buildup and its mineralization by phosphatases; this could be an extra benefit of conservation agriculture (CA) in soils. To study the impact of long-term CA on soil organic and inorganic P fractions and their distribution, a long-term field trial was conducted under a maize-based cropping system with different tillage (zero tillage (ZT), permanent bed (PB) and conventional till (CT) and cropping system (maize–wheat–mungbean (MWMb), maize–chickpea–sesbania (MCS), maize–mustard–mungbean (MMuMb) and maize–maize–sesbania (MMS)). Phosphorus dynamics were studied through sequential fractionation (organic and inorganic P) at 0–5 and 5–15 cm soil depth. The findings showed that a higher amount of soluble and loosely bound P (SL-P) was detected in ZT among the inorganic P fractions, whereas iron-bound P (Fe-P), aluminum-bound P (Al-P), reductant soluble P (RES-P) and calcium-bound P (Ca-P) were found higher in CT in both soil depths. Among Organic-P fractions, moderately labile and non-labile Po was found higher in PB and ZT but, in the case of labile Po, it was found insignificant with respect to tillage operations. Significant synergistic effects of winter legume (chickpea) with summer legumes (sesbania and mungbean) in crop rotation were observed on SL-P, Labile Po, Humic acid-Po, Alkaline phosphatase and MBP at 0–5 and 5–15 cm soil depths. Given the potential relevance of understanding P dynamics for efficient P management in long-term conservation agriculture practices, our findings offers critical new insight for the P management for sustainable development. [ABSTRACT FROM AUTHOR]

Understanding sediment phosphorus (P) compounds is essential to managing P in lake sediments because P speciation will determine bioavailability and reactivity. Little is known about organic P (Po) in hardwater eutrophic lakes in the North American Great Plains, or the role of metals in Po cycling. Sediment cores (0–12 cm deep) collected from four lakes from the Qu’Appelle chain in Saskatchewan, Canada, were sectioned by depth and analyzed by solution P nuclear magnetic resonance spectroscopy to characterize P forms. Concentrations and pools of calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), and aluminum (Al) were also determined. A range of P compounds was detected with significant interactions between lakes and depth for orthophosphate, phytate and DNA, and significant differences among lakes or with depth for polyphosphates and phosphonates. The main class of Po compounds identified in all lakes was orthophosphate diesters, including phospholipids and DNA, typical of living biota, suggesting that P immobilized by microbes and algae is an important pool in the sediments of these lakes. There were significant differences in metal concentrations among the lakes. In three lakes, Ca concentrations were high, and P was tightly bound with Ca compounds of low solubility. In the fourth lake with lower Ca concentrations, P appeared to be loosely bound to Al and Fe compounds. Our study indicates that there were significant differences in P compounds and the factors controlling their cycling among these four lakes in the same chain, which has implications for P management and water quality control.

Organic phosphorus (P o) is a large component of soil P, but it is often unavailable for plant uptake. Purple acid phosphatases (PAP) can hydrolyze a wide range of P o , playing an important role in P o utilization by plants. In this study, we investigated a novel secretary PvPAP1 from the As-hyperaccumulator Pteris vittata , which can effectively utilize exogenous P o , including adenosine triphosphate (ATP) and phytate. Unlike other PAP, PvPAP1 was abundantly-expressed in P. vittata roots, which was upregulated 3.5-folds under P-deprivation than P-sufficient conditions. When expressed in tobacco, its activity in the roots of PvPAP1-Ex lines was ∼8 folds greater than that in wild-type (WT) plants. Besides, PvPAP1 exhibited its secretory ability as evidenced by the sapphire-blue color on the root surface after treating with 5-bromo-4-chloro-3-indolyl phosphate. In a long-term experiment using sand media, PvPAP1 -expressing tobacco plants showed 25–30 % greater root biomass than WT plants when using ATP as the sole P source. This is because PvPAP1- expression enhanced its phosphatase activity by 6.5–9.2 folds in transgenic tobacco, thereby increasing the P contents by 39–41 % in its roots under ATP treatment and 9.4–30 % under phytate treatment. The results highlight PvPAP1 as a novel secreted phosphatase crucial for external P o utilization in P. vittata , suggesting that PvPAP1 has the potential to serve as a valuable gene resource for enhancing P o utilization by crop plants. [Display omitted] • A novel purple acid phosphatase gene PvPAP1 was isolated from P. vittata; • PvPAP1 was upregulated under P-deprivation compared to P-sufficient conditions; • Expressing PvPAP1 enhanced phosphatase activity in plants; • Expressing PvPAP1 promoted plant growth using ATP as the sole P source; • Expressing PvPAP1 increased P uptake in plant roots under ATP and phytate treatment. [ABSTRACT FROM AUTHOR]

Background: Manures and synthetic fertilisers can affect soil pH and plant-microbe processes and thus influence P forms and composition. Aims: The objective of this study was to examine the effects of the 40-year application of synthetic fertilisers or pig manure combined with synthetic fertilisers on the P forms and composition and the response of corn growth and yield to changes in P availability. Methods: A long-term field experiment with unfertilised, urea, urea+superphosphate, pig manure+urea and pig manure+urea+superphosphate fertilised soils was studied. 31P nuclear magnetic resonance spectroscopy was used to quantify P compounds. Results: The maximum corn yield was found when adding pig manure+urea, despite Olsen-P was lower than on adding manure+superphosphate. Other monoester P compounds, typically related to microbial biomass and processes were highest on adding pig manure+urea. When adding superphosphate+urea+pig manure a reduction of these P compounds was observed as well as the highest accumulation of inositol hexakisphosphate (IHP). Synthetic fertilisers increased Olsen-P, orthophosphate and other monoester and total IHP and largely decreased soil pH. The addition of pig manure greatly increased the stereoisomers of IHP (myo-IHP, scyllo-IHP, neo-IHP, and D-chiro-IHP) and the concentration of orthophosphate diesters. D-chiro-IHP was not found in unfertilised soils while neo-IHP was not detected in synthetically fertilised soils. Conclusions: P compounds related to microbial processes, such as other monoester, increased when adding pig manure. Additions of superphosphate on top of manures reduced other monoester, while they increased on adding synthetic fertilisers alone. Unfertilised soils were virtually free of P compounds related to microbial processes. [ABSTRACT FROM AUTHOR]

Drylands are arid and semi-arid areas whose main feature is their low level of precipitation. They cover nearly half of Earth's land surface and are distributed worldwide, constituting the planet's largest biome. Dryland soils have low fertility, are greatly affected by climate variability, and are vulnerable to wind and water erosion. The phosphorus-rich soil dust traveling by aeolian processes from drylands is the main source of P for the global primary productivity in P-limited areas, a fact that highlights the importance of arid and semiarid areas in the global nutrient budget. This review discusses the development of dryland soils, the sources of P in drylands, the C, N, P, relation in dryland soils, the fractionation and bioavailability of P, and biotic and abiotic factors affecting the P in drylands. Finally, the dynamic of P in biological soil crusts and resource islands is discussed. Combined, they contribute to the surface organic matter pools, alter the soil fertility, and are determinant factors in P's availability in dryland soils. We conclude the review by highlighting the gaps in knowledge that should be addressed in future research regarding biological and abiotic processes that determine the dynamics of P in drylands. [ABSTRACT FROM AUTHOR]

Abstract Background Land-use change and forest management may alter soil organic matter (SOM) and nutrient dynamics, due in part to alterations in litter input and quality. Acacia was introduced in eucalypt plantations established in the Congolese coastal plains to improve soil fertility and tree growth. Eucalypt trees were expected to benefit from N2 fixed by acacia. However, some indicators suggest a perturbation in SOM and P dynamics might affect the sustainability of the system in the medium and long term. In tropical environments, most of the nutrient processes are determined by the high rates of organic matter (OM) mineralization. Therefore, SOM stability might play a crucial role in regulating soil-plant processes. In spite of this, the relationship between SOM quality, C and other nutrient dynamics are not well understood. In the present study, OM quality and P forms in forest floor and soil were investigated to get more insight on the C and P dynamics useful to sustainable management of forest plantations. Methods Thermal analysis (differential scanning calorimetry (DSC) and thermogravimetry (TGA)) and nuclear magnetic resonance (solid state 13C CPMASS and NMR and 31P-NMR) spectroscopy have been applied to partially decomposed forest floor and soils of pure acacia and eucalypt, and mixed-species acacia-eucalypt stands. Results Thermal analysis and 13C NMR analysis revealed a more advanced stage of humification in forest floor of acacia-eucalypt stands, suggesting a greater microbial activity in its litter. SOM were related to the OM recalcitrance of the forest floor, indicating this higher microbial activity of the forest floor in this stand might be favouring the incorporation of C into the mineral soil. Conclusions In relation with the fast mineralization in this environment, highly soluble orthophosphate was the dominant P form in both forest floor and soils. However, the mixed-species forest stands immobilized greater P in organic forms, preventing the P losses by leaching and contributing to sustain the P demand in the medium term. This shows that interactions between plants, microorganisms and soil can sustain the demand of this ecosystem. For this, the forest floor plays a key role in tightening the P cycle, minimizing the P losses.

In an agro-ecosystem, phosphorus (P) is found in organic and an inorganic form which includes soluble P, sorbed P and mineral bounded P. In soil, added P sources undergo various soil processes like mineralization, immobilization, precipitation, weathering, dissolution, sorption and desorption. For understanding the P dynamics in clay loam (Vertic Ustropept) soil, the present study was undertaken in P dynamics under rhizosphere and non-rhizosphere environment of maize in Long Term Fertilizer Experiment at Tamil Nadu Agricultural University, Coimbatore. The results revealed that the fractions of various pools of inorganic NaOH extractable Fe - P, H2SO4 extractable Ca-P, NH4F extractable Al-P, NH4Cl extractable Saloid P and Na citrate - Dithionate extractable Reductant soluble P were dominant in the non-rhizospheric soil than rhizospheric environment. The order of inorganic P fractions in the non-rhizospheric and rhizospheric region of the soil was found as Ca-P > Fe-P > Al-P > Reductant soluble-P > Saloid P and the knee-high stage of the non - rhizosphere soil recorded the highest inorganic as well organic P fractions. Irrespective of P fractions, Ca - P was recorded high (192.5 & 186.7 mg kg-1) followed by Fe - P (40.8& 34.9 mg kg-1) at a knee-high stage in non-rhizosphere and rhizosphere, respectively. Practising various nutrient management systems, application of 100% recommended dose of fertilizer along with FYM @ 10 t ha-1 (T8) recorded significant changes in all inorganic (Ca-P, Fe-P, Al-P, Reductant soluble-P, Saloid P), organic fractions and also Total P followed by 150% NPK (T3) in sandy clay loam soil. Nowadays, increasing demand for P fertilizer in India, judicious use of P fertilizer is important. Despite that, intensively cultivated soils have a lot of P reserves like organic and inorganic P pools and effective way of P transformation management could reduce the quantum of P fertilization in soil. [ABSTRACT FROM AUTHOR]

Processes governing soil organic matter (SOM) decomposition and mineralization are important for soil fertility and ecosystem sustainability. However, in the sub-Saharan region, limited work has been conducted on SOM dynamics; therefore, there was an imperative need for this study. The objective of this study was to determine the phosphorus (P) and nitrogen (N) dynamics in soil under different tillage and fertilizer management practices. The field trial was arranged as a randomized split plot design, with tillage forming the whole plot and the fertilizer application rate being the sub-plot. The tillage techniques were no-till (NT), annual tillage (CT-ANNUAL) and conventional tillage every fifth season (CT-Y5), whereby NT was practiced for four consecutive seasons, and in the fifth season, conventional tillage was employed. For all these tillage techniques, urea fertilizer was applied in amounts of 60, 120 and 240 kg N ha−1 with a control for each tillage treatment. Ammonium and nitrate levels were determined calorimetrically. Sulfuric acid, at 1 M, along with 0.057 M ascorbic acid and molybdate reagent were used to extract the organic P from the soil and extractable P. The total N, ammonium, total P, organic P and extractable P in the surface soil under NT were higher (p < 0.05) compared to the values of both CT-Y5 and CT-ANNUAL. The high levels of total N, N mineralization, total P, organic P and extractable P under NT, compared to CT-Y5 and CT-ANNUAL, at the depth of 0–10 cm may be attributed to the accumulation of crop residues on the surface and less soil disturbance. Furthermore, nitrate was found in higher (p < 0.05) concentrations under CT-ANNUAL compared to CT-Y5 at all the application rates and depths. The ploughing of soil under CT-ANNUAL improves the aeration, which accelerates the decomposition of organic material and mineralization of organic N and P into soluble forms. No-till, at 60 kg N ha−1 and a 0–10 cm soil depth, had optimum total N, nitrate, ammonium, total P and organic P values, thus showing its salient impact on the maintenance of soil fertility. However, the conclusion drawn from this study is that CT-Y5, due to its average N and P pools, can be recommended to under-resourced farmers in sub-Saharan preferentially over both NT and CT-ANNUAL, because it does not require advanced technology and equipment and it sustains an average soil fertility.

Over the past decade, scientific studies have increasingly concentrated on the effects of global phosphorus (P) scarcity on food security. A comprehensive strategy that considers demand reduction and recycling possibilities is needed to address the global P scarcity. Reduced tillage along with crop residue retention could decrease fixation of P in soil, improve labile P content and enhance organic-P (Po) buildup and its mineralization by phosphatases; this could be an extra benefit of conservation agriculture (CA) in soils. To study the impact of long-term CA on soil organic and inorganic P fractions and their distribution, a long-term field trial was conducted under a maize-based cropping system with different tillage (zero tillage (ZT), permanent bed (PB) and conventional till (CT) and cropping system (maize–wheat–mungbean (MWMb), maize–chickpea–sesbania (MCS), maize–mustard–mungbean (MMuMb) and maize–maize–sesbania (MMS)). Phosphorus dynamics were studied through sequential fractionation (organic and inorganic P) at 0–5 and 5–15 cm soil depth. The findings showed that a higher amount of soluble and loosely bound P (SL-P) was detected in ZT among the inorganic P fractions, whereas iron-bound P (Fe-P), aluminum-bound P (Al-P), reductant soluble P (RES-P) and calcium-bound P (Ca-P) were found higher in CT in both soil depths. Among Organic-P fractions, moderately labile and non-labile Po was found higher in PB and ZT but, in the case of labile Po, it was found insignificant with respect to tillage operations. Significant synergistic effects of winter legume (chickpea) with summer legumes (sesbania and mungbean) in crop rotation were observed on SL-P, Labile Po, Humic acid-Po, Alkaline phosphatase and MBP at 0–5 and 5–15 cm soil depths. Given the potential relevance of understanding P dynamics for efficient P management in long-term conservation agriculture practices, our findings offers critical new insight for the P management for sustainable development.

Most plants living in tropical acid soils depend on the arbuscular mycorrhizal (AM) symbiosis for mobilizing low-accessible phosphorus (P), due to its strong bonding by iron (Fe) oxides. The roots release low-molecular-weight organic acids (LMWOAs) as a mechanism to increase soil P availability by ligand exchange or dissolution. However, little is known on the LMWOA production by AM fungi (AMF), since most studies conducted on AM plants do not discriminate on the LMWOA origin. This study aimed to determine whether AMF release significant amounts of LMWOAs to liberate P bound to Fe oxides, which is otherwise unavailable for the plant. Solanum lycopersicum L. plants mycorrhized with Rhizophagus irregularis were placed in a bicompartmental mesocosm, with P sources only accessible by AMF. Fingerprinting of LMWOAs in compartments containing free and goethite-bound orthophosphate (OP or GOE-OP) and phytic acid (PA or GOE-PA) was done. To assess P mobilization via AM symbiosis, P content, photosynthesis, and the degree of mycorrhization were determined in the plant; whereas, AM hyphae abundance was determined using lipid biomarkers. The results showing a higher shoot P content, along with a lower N:P ratio and a higher photosynthetic capacity, may be indicative of a higher photosynthetic P-use efficiency, when AM plants mobilized P from less-accessible sources. The presence of mono-, di-, and tricarboxylic LMWOAs in compartments containing OP or GOE-OP and phytic acid (PA or GOE-PA) points toward the occurrence of reductive dissolution and ligand exchange/dissolution reactions. Furthermore, hyphae grown in goethite loaded with OP and PA exhibited an increased content of unsaturated lipids, pointing to an increased membrane fluidity in order to maintain optimal hyphal functionality and facilitate the incorporation of P. Our results underpin the centrality of AM symbiosis in soil biogeochemical processes, by highlighting the ability of the AMF and accompanying microbiota in releasing significant amounts of LMWOAs to mobilize P bound to Fe oxides.

Most plants living in tropical acid soils depend on the arbuscular mycorrhizal (AM) symbiosis for mobilizing low-accessible phosphorus (P), due to its strong bonding by iron (Fe) oxides. The roots release low-molecular-weight organic acids (LMWOAs) as a mechanism to increase soil P availability by ligand exchange or dissolution. However, little is known on the LMWOA production by AM fungi (AMF), since most studies conducted on AM plants do not discriminate on the LMWOA origin. This study aimed to determine whether AMF release significant amounts of LMWOAs to liberate P bound to Fe oxides, which is otherwise unavailable for the plant. Solanum lycopersicum L. plants mycorrhized with Rhizophagus irregularis were placed in a bicompartmental mesocosm, with P sources only accessible by AMF. Fingerprinting of LMWOAs in compartments containing free and goethite-bound orthophosphate (OP or GOE-OP) and phytic acid (PA or GOE-PA) was done. To assess P mobilization via AM symbiosis, P content, photosynthesis, and the degree of mycorrhization were determined in the plant; whereas, AM hyphae abundance was determined using lipid biomarkers. The results showing a higher shoot P content, along with a lower N:P ratio and a higher photosynthetic capacity, may be indicative of a higher photosynthetic P-use efficiency, when AM plants mobilized P from less-accessible sources. The presence of mono-, di-, and tricarboxylic LMWOAs in compartments containing OP or GOE-OP and phytic acid (PA or GOE-PA) points toward the occurrence of reductive dissolution and ligand exchange/dissolution reactions. Furthermore, hyphae grown in goethite loaded with OP and PA exhibited an increased content of unsaturated lipids, pointing to an increased membrane fluidity in order to maintain optimal hyphal functionality and facilitate the incorporation of P. Our results underpin the centrality of AM symbiosis in soil biogeochemical processes, by highlighting the ability of the AMF and accompanying microbiota in releasing significant amounts of LMWOAs to mobilize P bound to Fe oxides. [ABSTRACT FROM AUTHOR]

Increasing cropping intensity may affect phosphorus (P) recycling through crop residue inputs, which may differ in soils with different productivity, P adsorption capacity, and P fertilization level. In three crop sequences: Soybean (Glycine max L. Merr.) monoculture (S–S), Maize (Zea mays L.) monoculture (M-M), and Wheat (Triticum aestivum L.)/Soybean as a double crop (W/S) in a Vertisol and a Mollisol; we assessed the long-term effect of the crop sequences on soil inorganic P (Pi) and organic P (Po) fractions, and the short-term effect of P fertilization on soil Pi and Po fractions, P uptake, and grain yield. Two P fertilization levels (50 kg P ha−1, and control) were established in 2016 on long-term experiments that included S–S, W/S, and M-M. Bray1-P, as well as total P, Po, and Pi in both the coarse soil (> 53 μm) fraction (CF) and the NaHCO3 extract, and accumulated yield and P uptake were measured. In the long-term, the crop sequences did not change soil P fractions, but Po-CF and Pi-CF showed similar values in both soils, suggesting less soil-type dependence than in other labile P fractions. In the short-term, the P fertilization only increased the extractable Pi fractions (16% in the Mollisol and 25% in the Vertisol), suggesting that P in the CF was not a sink of P fertilizer. Our study showed that P fertilization in different crop sequences may increase labile P fractions and P recycling depending on soil type, a useful tool to develop P fertilization strategies at the crop sequence level. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an essential nutrient, but European forest ecosystems are experiencing widespread declines in soil P concentrations. To clarify the roles of ectomycorrhizal (EM) and saprotrophic (SAP) fungi in P cycling in forest soils that differ in inorganic and organic P availability, we conducted an ingrowth tube (IGT) experiment over 18 months of exposure in five beech (Fagus sylvatica L.) forests in Germany. To separate the contributions of both fungal guilds in situ, two different types of IGTs were used: (i) open IGTs with micromesh windows to allow EM fungi to regrow into the tubes, and (ii) closed IGTs (without mesh windows) in which recolonization by EM hyphae was restricted. We then measured phosphomonoesterase, phosphodiesterase, peroxidase, and phenoloxidase activities in EM (open IGTs) and SAP (closed IGTs) dominated fungal assemblages. Shifts in fungal assemblages occurred over time, but the speed and extent of those shifts differed between the five forest sites. In three forest sites fungal community composition shifted toward greater dominance of EM fungi in open IGTs than in closed IGTs after a period of 18 months, but these changes were not apparent in two other sites. Although shifts in fungal community composition were noticeable between treatments, we found no effect on phosphomonoesterase activity. Since phosphomonoesterase is present in both fungal guilds, this indicates functional redundancy of fungi. Phosphodiesterase activity was slightly reduced in SAP dominated IGTs, indicating that SAP fungi contribute to phosphodiesterase activity to a lesser extent than do EM fungi. P cycling enzymes did not appear to have been influenced by the total P stocks of the forest sites but may have been affected by additional abiotic factors. Contrary to our expectation, phenoloxidase activity was unaffected by fungal community composition, and only peroxidase activity was higher in SAP dominated IGTs, indicating that the contribution of EM fungi to degradation of complex organic material is driven by the need to obtain nutrients in addition to C. Overall, the results of this study contribute to a better understanding of the roles of EM and SAP fungi in P cycling in forest soils.

The purpose of this study was to evaluate how the different phosphorus fractions in soils contribute to plant uptake, based on the combination between the sequential P fractionation developed by Hedley and path analysis. Successive crops were grown on soil samples with different P legacies, taken from the 0.00–0.10 m layer of an untilled Latossolo Vermelho (Rhodic Hapludox). The experimental treatments consisted of three annual P rates (0 kg P ha−1–P0; 157 kg P ha−1–P157; 314 kg P ha−1–P314). In a greenhouse, 15 successive crops of millet, black oat, corn, soybean, crotalaria and rye were grown in pots, with six replications. Phosphorus fractions in the soil were evaluated before the first crop and after the third and 15th crop. At the beginning of cultivation, the labile P fractions were buffered by the less labile P fractions in soils fertilized with the highest P rate (P314). After the 15 crop cycles, labile P was buffered, mainly by labile and non-labile organic P fractions. In soils without previous P fertilization and intermediate fertilizer rates, there was a significant contribution of organic P fractions to the moderately plant-available inorganic P pool. The organic P fraction only contributed to plant nutrition in soils fertilized with high P rates after depletion of the inorganic P pool. The conclusion was drawn that all soil P fractions can potentially provide plants with P, whereas the contribution of these P fractions depends on the P fertilization history. [ABSTRACT FROM AUTHOR]

Long‐term P Fertiliser application increases soil phosphorus (P) labile fractions, which can be associated with crop P uptake and grain yield and are useful to improve fertilizer recommendations. Research aims were to evaluate in long‐term experiments with different P Fertiliser application in a Mollisol and a Vertisol: (a) the changes of soil P fractions and (b) the relationship between soil P fractions with long‐term P Fertiliser application, with accumulated apparent P budget, grain P, total P uptake, soybean (Glycine max L.Merr.) and maize (Zea mays L.) grain yield. Soil P fractions were measured after 1 and 9 year since the beginning of the long‐term experiments. Experiments included an initial Fertiliser application rate of 200 kg P ha−1 and annual P Fertiliser application rate of 36 kg P ha−1. Bray1‐P, total, organic, and inorganic P in fine (<53 μm) and coarse (>53 μm) (CF) soil fractions, and in NaHCO3 extract were measured. Initial P Fertiliser application increased inorganic and total P fractions. However, Bray1‐P, total P in NaHCO3 extract and in the CF were the fractions that most increased with continuous long‐term P Fertiliser application in both sites. In the Mollisol, maize grain yield was unrelated to long‐term P Fertiliser application. In the Vertisol, total P in NaHCO3 extract, and total and organic P in the CF were more closely related to soybean grain yield than Bray1‐P. We proposed soil P indices of labile inorganic and organic P that showed close relationships with soybean grain yield and may be useful to improve the diagnosis of P soil fertility. [ABSTRACT FROM AUTHOR]

Background: Land-use change and forest management may alter soil organic matter (SOM) and nutrient dynamics, due in part to alterations in litter input and quality. Acacia was introduced in eucalypt plantations established in the Congolese coastal plains to improve soil fertility and tree growth. Eucalypt trees were expected to benefit from N2 fixed by acacia. However, some indicators suggest a perturbation in SOM and P dynamics might affect the sustainability of the system in the medium and long term. In tropical environments, most of the nutrient processes are determined by the high rates of organic matter (OM) mineralization. Therefore, SOM stability might play a crucial role in regulating soil-plant processes. In spite of this, the relationship between SOM quality, C and other nutrient dynamics are not well understood. In the present study, OM quality and P forms in forest floor and soil were investigated to get more insight on the C and P dynamics useful to sustainable management of forest plantations. Methods: Thermal analysis (differential scanning calorimetry (DSC) and thermogravimetry (TGA)) and nuclear magnetic resonance (solid state 13C CPMASS and NMR and 31P-NMR) spectroscopy have been applied to partially decomposed forest floor and soils of pure acacia and eucalypt, and mixed-species acacia-eucalypt stands. Results: Thermal analysis and 13C NMR analysis revealed a more advanced stage of humification in forest floor of acacia-eucalypt stands, suggesting a greater microbial activity in its litter. SOM were related to the OM recalcitrance of the forest floor, indicating this higher microbial activity of the forest floor in this stand might be favouring the incorporation of C into the mineral soil. Conclusions: In relation with the fast mineralization in this environment, highly soluble orthophosphate was the dominant P form in both forest floor and soils. However, the mixed-species forest stands immobilized greater P in organic forms, preventing the P losses by leaching and contributing to sustain the P demand in the medium term. This shows that interactions between plants, microorganisms and soil can sustain the demand of this ecosystem. For this, the forest floor plays a key role in tightening the P cycle, minimizing the P losses. [ABSTRACT FROM AUTHOR]

Soil samples (from Czech and German long term field experiments) were used for estimating soil phosphorus (P) fractions. More then 100 topsoil (0-30 cm) samples from different fertilizing treatments were taken. These were analysed for P in soil solution (PCaCl2), exchangeable sorbed P (Pex) and bioavailable P. The methods used were 0,01M CaCl2 extracts, anion exchange (AE) membranes, Doppel-Lactat (PDL) and Mehlich 3 (PM3). Other fractions analysed were total inorganic (Pin), total (PM-tot) and organic (Porg) P estimated with Marks (1977) fractionation, P sorbed on Fe and Al (PFeAl) and residual P (Par). Comparison of medians appeared to be better for evaluating extraction abilities. Phosphorus fractions increased in the following order: [Par =100%]; PCaCl2 (0.1%) < Pex (10%) < PDL (12%) < PM3 (17%) < Pin (25%) < Porg (38%) < PM-tot (60%) < PFeAl (62%). Low amounts of Pin, Porg and PM-tot did not verified the applicability of Marks fractionation for the set of studied soils. Close correlations at α

An incubation study with fresh, frozen, and dried clover and rye-grass shoots gathered in autumn was performed in the laboratory (43 days). The aim was to study inorganic and organic phosphorus (P) release from plant material during decomposition without soil. Plant materials (2 cm size) were mixed with small glass beads and placed in large syringes for consecutive water extractions on 7 occasions. Leachates were analysed for inorganic and total P. At the first leaching event, 8% of total crop P was released from fresh, 24% from frozen and 27% from dried plant material. During decomposition, both inorganic and organic P was released following first order kinetics, with grass releasing mostly inorganic P and clover mostly organic P. After 43 days, 42%–50% of total crop P from fresh, 49%–51% from frozen and 57%–69% from dried material was released, with significant differences between treatments. Using the results in calculations on field scale showed that P released from overwintering crops under cold climate conditions can amount to several kg P ha−1. Thus, senescence of overwintering aboveground biomass can be a significant source for P leaching from soils.

Tree species establish mycorrhizal associations with both ectomycorrhizal (EM) and arbuscular mycorrhizal fungi (AM), which play crucial roles in facilitating plant phosphorus (P) acquisition. However, little attention has been given to the effects of EM and AM species on soil P dynamics and the underlying mechanisms in subtropical forests, where P availability is typically low. To address this knowledge gap, we selected two EM species ( Pinus massoniana - PM and Castanopsis carlesii - CC) and two AM species ( Cunninghamia lanceolata - Chinese fir, CF and Michelia macclurei - MM) in a common garden established in 2012 in subtropical China. We investigated soil properties (e.g., pH, soil organic carbon, total nitrogen, and dissolved organic nitrogen), soil P fractions, phospholipid fatty acids (PLFAs), enzyme activities, foliar manganese (Mn) concentration, and foliar nutrients and stoichiometry. Our findings revealed that soils hosting EM species had higher levels of resin P, NaHCO 3 -Pi, extractable Po, total P, and a greater percentage of extractable Po to total P compared to soils with AM species. These results indicate that EM species enhance soil P availability and organic P accumulation in contrast to AM species. Moreover, EM species exhibited higher P return to soil (indicated by higher foliar P concentrations) when compared to AM species, which partly explains higher P accumulation in soils with EM species. Additionally, resin P showed a positive correlation with acid phosphatase (ACP) activity, whereas no correlation was found with foliar Mn concentration, which serves as a proxy for the mobilization of sorbed soil P. Such findings indicate that organic P mineralization has a more substantial impact than inorganic P desorption in influencing P availability in soils hosting both EM and AM species. In summary, our study contributes to a more comprehensive understanding of the effects of mycorrhizal associations on soil P accumulation in subtropical forests and provide valuable insights into plant-soil interactions and their role in P cycling in regions with limited P availability., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Lian, Xu, Yang, Yue and Peñuelas.)

Important tools for the investigation of phosphorus (P) in soil are the acid digestion in aqua regia (AR) for total P, the sequential P fractionation (SF), 31P nuclear magnetic resonance (31P-NMR) spectroscopy and P K-edge X-ray absorption near-edge structure (P K-edge XANES) spectroscopy. The objective of the present study was to critically compare the outcomes of these methods in order to improve the data evaluation and interpretation. For this purpose, we analyzed total P (Pt) and the P speciation of three groups of soil samples (extremely P-rich, P-poor acidic, P-poor to P-rich alkaline). The recovery of the extracted P between the different methods depended on the soil characteristics, resulting in recommendations for improving the P extraction. The 31P-NMR spectra were calibrated to a monoester standard which provided a better consistency of the peak position in comparison to the shifting of the orthophosphate peak to 6.0 ppm. The SF and 31P-NMR agreed in the inorganic P (Pi) and Po proportions, especially in the alkaline fraction. The correlation between Po from P K-edge XANES and diesters from 31P-NMR indicated that P K-edge XANES detected rather diesters than monoesters in soils. Correlations between SF and P K-edge XANES results confirmed the presence of specific Pi species in the sequentially extracted fractions. However, the SF is still relatively unspecific for interpreting Po species from a certain fraction. A more specific description of the Po composition in fractions from the SF requires investigation of these fractions by 31P-NMR and P K-edge XANES. [ABSTRACT FROM AUTHOR]

Aims: Phosphorus (P) is a limited nutrient in highly weathered subtropical or tropical forest soils and it is unclear how both the cycling and availability of P will respond to future global warming and nitrogen (N) deposition. This study aims to evaluate the influence of soil warming and N deposition on soil P fractions in relation to plant growth and P uptake. Methods: We carried out a field mesocosm bioassay experiment with a soil warming and N addition treatment in a factorial design and measured soil Hedley P fraction and P uptake of the Chinese fir (Cunninghamia lanceolata) seedlings. Results: Soil warming significantly increased soil easily-available and moderately-available inorganic phosphorus (Pi) but had no effect on soil easily-available and moderately-available organic P (Po), or on plant growth or plant biomass P, and decreased soil microbial biomass P (MBP). Nitrogen addition increased plant growth and leaf biomass P, but had no effect on soil Pi and MBP, and decreased soil moderately-available Po and leaf P concentration. There were no interactions between soil warming and nitrogen on Hedley P fractions. None of the Hedley P fractions had correlated with plant height and diameter growth or with plant P uptake. Conclusions: Our results suggest that the Hedley P fractions do not reflect soil P availability and that the growth of the Chinese fir is not limited by soil P availability in this subtropical Ultisol, rather it is most likely limited by N and water availability based on the results from this bioassay experiment. [ABSTRACT FROM AUTHOR]

Understanding soil P transformation is critical to optimizing P supply to crops while minimizing P loss to water. Nitrogen application in agricultural fields can cause acidification, changing soil chemistry and altering P cycling. In a calcareous vegetable field in China, 13 years of N application (1172 kg N ha−1 year−1) significantly decreased soil pH, CaCO3, and Mehlich-3 extractable (M3) Mg and increased M3-Fe and M3-Al. Nitrogen addition also increased microbial biomass C (MBC), decreased alkaline phosphomonoesterase (ALP) activity, and changed the total bacterial and phoD-harboring bacterial community composition. Soil total P, Olsen-P, and M3-P were not affected by N fertilization, but there were significant increases in soil total organic P (Po), NaOH-extractable Po, and the proportion of orthophosphate diesters. Redundancy analysis showed that soil pH, organic C, CaCO3, and ALP activity had significant effects on the compositions of soil P form (P < 0.05) and could explain 36.4, 13.3, 27.5, and 10.6% of the total variances observed in the composition of P forms. This suggests that soil acidification from N application in this P-rich calcareous soil altered soil abiotic P cycling processes through increasing the chemical adsorption of Po by Fe and Al. It also altered biotic P cycling processes by increasing microbial P uptake and immobilization and decreasing P biochemical mineralization, resulting in Po accumulation. [ABSTRACT FROM AUTHOR]

The efficient use of phosphorus (P) in agriculture should rely on accurate soil P tests (SPT). Organic P contributes to P supply to plants; however, it is not usually taken into account in assessing P fertilizer requirements. We hypothesized that there would be an increased accuracy of bicarbonate extraction as SPT in predicting P uptake by plants if total P (TP) in this soil extract is taken into account. We conducted a soil P depletion experiment with 36 soils involving four consecutive crops in pots. Molybdate‐reactive P (MRP) and total P were determined in extracts centrifuged at 19,000 g (Bic‐MRPC and Bic‐TPC) or not (Bic‐MRP and Bic‐TP). MRP in extracts explained <47% of the variance in the cumulative P uptake, while total P (centrifuged at 19,000 g or not) provided the most accurate estimation of P uptake (59% with Bic‐TP) and threshold values for fertilizer response (R2 = 0.58 with Bic‐TPc). When soils were separated in two groups according to their Ca carbonate equivalent to clay ratio, the variance in the cumulative P uptake explained by Bic‐MRP was above 63%, and that explained by Bic‐TP was above 73%. This separation also enabled more realistic estimation of the threshold values for fertilizer response. It can be concluded that the use of total P instead of MRP in bicarbonate extraction was promising in terms of improving its accuracy in assessing P fertilizer requirements. [ABSTRACT FROM AUTHOR]

Highlights • The high eucalyptus productivity indicates a high P scavenger efficiency by accessing successfully the stable P in the soil. • Organic phosphorus comprise an important pool of eucalyptus nutrition in highly weathered soils. • Hedley fractionation was a good indicator of potentially bioavailable P pools for the plant, as well as the citrate + oxalate method. • The available P pool was dependent on inorganic and occluded pools and the organic pool acted predominantly as a sink of P on available and inorganic pools. Abstract Phosphate fertilizers play an important role in plant nutrition. Different P fertilizer sources such as high-solubility (simple superphosphate, SSP), low-solubility (rock phosphate, RP) and complex superphosphate (CSP) are available for plant supplementation. The objective of this study was to investigate the short- and long-term redistribution of soil P after application of different P sources at establishment of an Eucalyptus forest stand. We carried out two experiments to identify the short- and long- term changes in a Brazilian Oxisol. To property identify the P pools in different times, Hadleýs fractionation methodology was applied to a long-term studies and citrate and oxalate to short-term. From zero to 180 days, the soluble P fractions were not altered in the non-fertilized treatment. Under SSP, a slight increase in this P fraction was found until 30 days, followed by a decrease in later evaluations. During the same period, a slight reduction in Pi extracted by citrate and oxalate was found under the control and a large reduction (approximately 50%) under the SSP treatment. Intermediate behavior was observed under the CSP and RP treatments, whereas there was an increase in P-citrate and P-oxalate until 30 days followed by a reduction afterwards. These results suggest that this pool comprises a potential bioavailability of P to plants. Different fertilizer sources did not increase the most recalcitrant P pool. However, different sources increased the organic P pool, mainly organic moderately labile P at long-term evaluations. Organic labile pools showed a fertilizer-specific response where CSP and RP increased respectively by 43% and 41% during the first year, and decreased to 39% in CSP treatment and 50% in RP treatment during the third year. Available P pool was highly dependent on inorganic and occluded pools and the organic pool acted predominantly as a sink of P on available and inorganic pools. The results reinforce the high level of recalcitrance of the organic pool and the fact that Eucalyptus plants must access pools of residual P in order to maintain their nutritional demands. [ABSTRACT FROM AUTHOR]

Purpose: Stream bank erosion is one of the main sources of suspended sediments in stream water, and it often carries phosphorus with it. With a controlled laboratory study, we investigated the changes in different forms of P in stream bank sediments at varying redox potentials. We hypothesized that there could be increases in labile forms of solid-phase P under low redox conditions.Materials and methods: Sediment samples representing four major stratigraphic units were collected from alluvial banks of Walnut Creek in Jasper County, Iowa: Camp Creek, Roberts Creek, and Gunder members of the Holocene-age De Forest Formation and pre-Illinoian till, a glacial deposit that is older than 500,000 years. We compared three treatments: no anaerobic incubation, anaerobic incubation, and anaerobic incubation with addition of glucose. After each treatment, soil P fractions were determined and classified as water-extractable P, labile P, slowly cycling P, stable P, and residual P. Labile P is extractable with 0.5 M NaHCO3, slowly cycling P is extractable with 0.1 M NaOH or 1 M HCl, stable P is extractable with concentrated HCl, and residual P is associated with acid-insoluble compounds in the soil.Results and discussion: Redox potential of the equilibrated systems was significantly less when sediments were incubated anaerobically than when they were not incubated, especially when glucose was added to the anaerobic incubation. Variations in redox potential did not significantly affect the total P, organic or inorganic stable P, or residual P in the sediments. In contrast, we found that the amount of inorganic labile P tended to increase at the same time that slowly cycling P associated with Fe decreased.Conclusions: The younger sediments, higher in the stratigraphic profile and with more organic matter, had greater labile P and slowly cycling P that was associated with Fe, reflecting a greater potential to contribute to elevated levels of P in the stream water if subjected to low redox potential in the stream environment. The forms of P in the four bank sediments were redistributed among the fractions by reducing conditions. There was an increase in the concentration of inorganic labile P, which coincided with a decrease in slowly cycling P associated with Fe, especially in the Holocene-age sediments. These sediments appear to have a greater potential to contribute to elevated levels of P in the stream water when they are subjected to low redox potential in the stream environment. [ABSTRACT FROM AUTHOR]

Phosphorus (P) K‐edge X‐ray absorption near‐edge structure (XANES) spectra of orthophosphate (oPO4) bound to soil FeIII minerals (e.g. ferrihydrite, goethite) show a pre‐edge signal at 2148–2152 eV. It is unknown whether organic P bound to FeIII oxyhydroxides also show this feature. Otherwise, Fe‐bound soil P may be underestimated by P K‐edge XANES spectroscopy, because a large portion of Fe oxyhydroxide‐bound P in soils is organic P. K‐edge XANES spectra were obtained for different organic P compounds present in soils [inositol hexaphosphate (IHP), glucose‐6‐phosphate (G6P), adenosine triphosphate (ATP)] after sorption to ferrihydrite or goethite and compared with spectra of oPO4 adsorbed to these minerals. P sorption to ferrihydrite increased in the sequence IHP ≪ G6P < oPO4 < ATP. P sorption to goethite increased in the sequence G6P < oPO4 ≪ ATP = IHP. Pre‐edge signals in P K‐edge XANES spectra of organic P adsorbed to Fe oxyhydroxides were markedly smaller compared with those of oPO4 adsorbed to these minerals and absent for FeIII oxyhydroxide‐bound ATP as well as goethite‐bound IHP. Linear combination fitting (LCF) performed on spectra of IHP, G6P or ATP adsorbed to ferrihydrite or goethite, using only spectra of FeIII oxyhydroxide‐bound oPO4 as reference compounds for Fe‐bound P, erroneously assigned >93% (ferrihydrite) or >41% (goethite) of Fe‐bound P to non‐Fe‐bound P species. Inclusion of FeIII oxyhydroxide‐bound IHP as reference compounds markedly increased the recovery of oxyhydroxide‐bound organic P. Thus, Fe‐bound soil P has probably often been underestimated by LCF in soil XANES studies where IHP adsorbed to ferrihydrite and to goethite were not included as reference compounds. Fe‐bound soil phosphorus (P) is probably often underestimated by LCF (linear combination fitting) conducted on P K‐edge X‐ray absorption near‐edge structure (XANES) spectra, unless inositol hexaphosphate (IHP) adsorbed to ferrihydrite and IHP adsorbed to goethite are included as reference compounds. [ABSTRACT FROM AUTHOR]

Agriculture significantly affects phosphorus (P) availability, thereby modifying P equilibrium. The objective of this study was to evaluate the effect of different crop sequences on the dynamics of soil P forms under no tillage. Soil samples were collected from a system of five sequences initiated in 1998. The agricultural sequences followed the scheme crop diversity (CD), crop-pasture (CP, without grasses), traditional crops 1 (TC1, for limited soils), traditional crops 2 (TC2), and traditional crops 3. TC3). The available P (Pe) was determined and soil P was fractionated. Organic P extracted with NaOH (PoNa) was analyzed by spectrometry UV–visible and IR. Under CP, the available P decreased in both organic and inorganic labile forms, whereas PoNa values increased. Higher Pe was observed in TC1and TC3. The E4/E6 rates showed that the systems with the lowest degree of aromaticity were CP, TC1 and TC3. These three management sequences presented high PoNa values and, from these values, CP showed lower values for Pe, indicating differences in the chemical quality of the molecule. The 1050/1260 spectra, which relates an aliphatic ester to an aromatic ester, indicated that the CP and TC3 ratios were 1.3 and 0.94, respectively. In other words, the predominant type of ester in CP is aliphatic and in TC3 predominant esters would be of the aromatic type. Crop rotations can produce changes in organic P forms, which will modify the predominant functional group and the way this nutrient interacts with the soil matrix. Inclusion of pastures in a rotation maintains plant-available P at lower levels. However, this is the sequence that keeps moderately labile P (PoNa) at higher levels. [ABSTRACT FROM AUTHOR]

Phosphorus (P) in soil exists both in organic and inorganic forms and their relative abundance could determine P supplying capacity of soil. Differential input of exogenous and plant-mediated phosphorus and carbon in soil under different land-uses could influence P availability and fertilizer P management. While the effect of land-use on soil organic carbon (SOC) is fairly well-documented, its effect on soil P fractions is relatively less known. We investigated the effect of different land-uses including rice-wheat, maize-wheat, cotton-wheat cropping systems and poplar-based agroforestry systems on soil P fractions and organic carbon accrual in soils. Total P concentration was the highest under agroforestry (569 mg P kg−1) and the lowest under maize-wheat (449 mg P kg−1) cropping systems. On the contrary, soils under rice-wheat had significantly higher available P concentration than the agroforestry systems, probably because of higher fertilizer P application in rice-wheat and prevailing wetland conditions during rice growth. In soils under sole cropping systems viz. rice-wheat, maize-wheat and cotton-wheat, inorganic P was the dominant fraction and accounted for 92.2-94.6% of total P. However, the soils under agroforestry had smaller proportion (73%) of total P existing as inorganic P. Among soil P fractions, water soluble inorganic P (0.13-0.26%) represented the smallest proportion inorganic P in soils under different land-uses. Agroforestry showed significantly (p < 0.05) higher concentrations of SOC than the other land-uses. Soil organic C was significantly correlated with soil P fractions. It was concluded that poplar-based agroforestry systems besides leading to C accrual in soil result in build-up of organic P and the P supplying capacity of soil. [ABSTRACT FROM AUTHOR]

Purpose: The effect on P uptake by plants after inoculation with P-mobilizing microorganisms may be modulated by soil properties, including natural microbiota. However, to put this theory into practical use, research is needed to shed new light on the soil factors which affect the capability of improving P nutrition in plants. The aim of this study was to assess how two P-mobilizing microorganisms, Trichoderma asperellum T34 and Bacillus subtilis QST713, influence P uptake by wheat plants in different soils; this will allow us to identify the soil properties which affect the efficiency of P nutrition in plants.Materials and methods: In a completely randomized experiment, wheat was grown in pots in a growing chamber in soils with Olsen P values ranging from 4.8 to 8.7 mg kg−1. The plants were inoculated with three treatments: T34, B. subtilis, and a non-inoculated control.Results and discussion: Overall, B. subtilis was more effective in increasing plant P uptake and in mobilizing soil P (measured as Olsen P values) than T34. In some soils, B. subtilis was the only treatment which increased Olsen P in the rhizosphere after cultivation. However, the effect of both microorganisms differed depending on the soil. For B. subtilis, phytase hydrolysable P, Olsen P, carbonates, the Feca/Fecbd ratio, and citrate-soluble P accounted for 92% of the variation in P uptake in inoculated plants (compared with the non-inoculated control). Most of these soil properties also accounted for 87% of the variation in the levels of shoot dry matter (DM) in B. subtilis-inoculated plants compared with shoot DM in the control plants. In addition, Olsen P, the Feca/Fecbd ratio, and phytase hydrolysable P in the NaOH extracts accounted for 82 and 74% of the variation in the effect of T34 on P uptake and shoot DM, respectively. Overall, the lower the initial Olsen P in the soil, the higher the P uptake caused by microorganisms.Conclusions: The initial availability of P and organic P in soil, in addition to other properties affecting P dynamics in the soil, may explain the triggering and efficiency of the P-mobilizing mechanisms in microorganisms. These are crucial in explaining the potential benefits to crops and, as a result, their practical use as a bio-fertilizer. [ABSTRACT FROM AUTHOR]

Marine basins with oxygen-depleted deep waters provide a natural laboratory to investigate the consequences of anoxic and sulfidic (i.e. euxinic) conditions for biogeochemical processes in seawater and sediments. In this study, we investigate the dynamics of the key nutrient phosphorus (P) and associated elements such as manganese (Mn), iron (Fe) and calcium (Ca) in the euxinic deep basin of the Black Sea. By examining water column particles with scanning electron microscope – energy dispersive spectroscopy and synchrotron-based X-ray absorption spectroscopy, we show that Mn(III/IV)-P is the key form of particulate P in the redoxcline. Other forms of particulate P include organic P, Fe(III)-P, and inorganic polyphosphates. Most inorganic P particles that are formed in the redoxcline subsequently dissolve in the underlying sulfidic waters, with the exception of some particulate Fe(III)-P that accounts for <1% of all P settling onto the seafloor. Organic P is the dominant source of P to the sediment. Most of this organic P is degraded in the upper 2 cm of the sediment. Results of sequential extractions and a 33 P radiotracer experiment point towards the formation of labile Ca-P and P adsorbed onto calcium-carbonate and clays and a role of these phases as a major sink of P in the sediment. The total P burial efficiency in the sediments is ∼27%, which is relatively high when compared to estimates for sediments in other euxinic basins such as the Baltic Sea (<12%). We suggest that the abundant presence of calcium carbonate may contribute to the more efficient sequestration of P in Black Sea sediments. [ABSTRACT FROM AUTHOR]

Increasing human population placed stress on the environment, as well as shifting in land use pattern to increase food production, significantly influence the dynamics of soil organic matter and associated nutrients (phosphorus) in terrestrial ecosystems. This review is based on the published work carried out in recent years and critically examines how the P cycling occurs within different terrestrial ecosystems, possible mechanisms involved in its transformation from one form to another and gaps to be investigated. In terrestrial ecosystems P mainly occurs as phosphate ion; generally precipitated with Ca, Al and Fe under varying pH conditions and become relatively immobile in soils. In agricultural fields, change in inorganic (Pi) and organic (Po) phosphorus are attributed due to fertilization and tillage while in forest and grasslands it is the matter of litter addition and its decomposition by microbes. Afforestation of grassland enhances the mineralization of organic matter and P availability through higher microbial activity, production of low molecular weight organic acids and root associations of mycorrhizae. Phosphorus losses primarily occur due to export in the form of erosion and product removal from ecosystem. Heavy export of P from terrestrial ecosystem accelerated the problem of eutrophication. Future studies should be focused on efficient practices to increase the use of accumulated surface P, estimating P bioavailability in soil and improved methods of runoff control to control P export into aquatic ecosystems. Optimization of practices and exploring novel approaches for sustainable production will maintain the enduring supply of this globally limited nutrient and reduce environmental consequences. DOI: http://dx.doi.org/10.5281/zenodo.854681