Phosphorus Mobilization Research Articles

Microbial recruitment and microbial ecological roles in soil nutrient cycling of Populus cathayana males and females

Soil nitrogen (N) availability influences plant production and soil nutrient cycling. However, how it influences sex-specific microbial community composition and rhizosphere nutrient cycling in dioecious plant species is poorly understood. We examined the rhizospheric bacterial and fungal community assemble and their influences on soil nutrient cycling under different N backgrounds in 30-year-old experimental stands and a soil microbial reshaping-controlled experiment. In comparison to male trees, female trees increased fungal community diversity, and the relative abundance of taxa related to nutrient availability; elevated phosphorus (P) mobilization by increasing acidic phosphatase activity and carboxylic acid release; and decreased the counts of denitrification nirS, nirK, and nosZ genes at high N supply. Males increased the nifH gene counts related to microbial N fixation at high N supply. Low N supply increased N fixation nifH gene counts in the rhizosphere of females. Males decreased bacterial and fungal diversity, increased enzymatic activities related to organic N and P mineralization, and elevated soil nitrate-nitrogen levels at low N supply. Our results indicate that sex-specific responses to N availability are associated with rhizospheric bacterial and fungal community composition and diversity and their effects on rhizospheric nutrient cycling, which may explain sex-specific resource utilization and niche differentiation.

Phosphate solubilization by rhizobacteria isolated from the rhizosphere of <i>Mimosa pudica</i>: an investigation into microbial mobilization of phosphorus

Phosphorus (P), in addition to nitrogen (N) and potassium (K), makes up the essential macronutrients needed by plants for growth and development. P is also one of the most abundant elements present in the Earth’s crust, and it occurs in both organic and inorganic forms. Although present in high concentrations, only a very minute amount is bioavailable to plants because of its poor solubility due to its high binding affinity to calcium, aluminium, and iron in the soil, forming insoluble calcium phosphate, aluminium phosphate, and ferrous phosphate, thereby becoming recalcitrant for plant utilization. In this study, bacteria isolated from the rhizosphere of Mimosa pudica from different locations at Nnamdi Azikiwe University, Awka, were screened for their ability to solubilize phosphate using point inoculation on Pikovskaya (PVK) media agar plates with tricalcium phosphate (Ca3(PO4)2) as a source of phosphate. The result showed that of the twenty-one (21) rhizobacteria screened, four (4) were able to solubilize phosphate with varying phosphate solubilizing index (PSI). The degrees of PSI were in the following order: isolate SVM5 and UBG13 > isolate UBG14> isolate FEA6. Isolate SVM5 and UBG13 had the highest PSI of 4.0, while isolate FEA6 had the lowest PSI of 3.1. The biochemical tests of the isolates revealed that the phosphate-solubilizing bacteria were members of Klebsiella spp. (FEA6, SVM5, and UBG14) and Pseudomonas sp. (UBG13). This study, therefore, suggests the need to include rhizobacteria as part of biofertilizer formulations to improve plant yield via the solubilization of phosphate into forms that are bioavailable for plant growth.

Mobility of Sediment and Phosphorus in a Small Stream During Artificial Flood Wave

This study investigates the dynamics of sediment and phosphorus transport in small streams affected by recurrent flood waves. The experiments were carried out in two streams with contrasting conditions: one in an agricultural headwater section, which serves as a sediment source, and the other in a mid-water section influenced by fish ponds. High-frequency data on suspended sediment and phosphorus concentrations were collected during several flood waves to assess how floods affect the transport regime, including the role of small reservoirs. The results showed that even initially clear water can mobilize significant amounts of sediment from the riverbed when discharge increases. Sediment mobilization was strongest at the beginning of the flood wave, with concentrations peaking early and then decreasing. Successive floods without additional sediment input led to a decrease in sediment concentrations, as the stream had already flushed out the available sediments. Hysteresis loops showed that most of the sediment transport occurred during the rising part of the flood wave, indicating that the sediment originated from the nearby streambed areas. Phosphorus was mobilized simultaneously with the sediment, and an almost linear relationship was observed between sediment concentration and total phosphorus (r = 0.979, p < 0.0001). However, only a fraction of the phosphorus was dissolved, so most of the phosphorus was bound to the sediment particles. Soluble reactive phosphorus showed a weaker correlation with sediment concentration (r = 0.272, p = 0.047). This shows how important it is to consider both sediment dynamics and phosphorus mobilization in event-based flood models.

Phosphorus Dynamics in Managed and Natural Soils: SEM-PLS Analysis of Vaccinium, Forest, and Grassland Ecosystems.

Phosphorus (P) availability in soils is often constrained by its accumulation in non-labile phosphorus (NLP) forms, limiting its accessibility to plants. This study examines how soil physical properties, chemical characteristics, and climatic conditions influence phosphorus fractionation and the transformation of NLP into plant-available labile phosphorus (LP). Utilizing global structural equation modeling (SEM), we found that silt content enhances organic phosphorus fractions, including NaHCO3-Po and NaOH-Po. In the upper 30 cm of soil, pH decreases the availability of NaHCO3-Po and NaOH-Po while stabilizing NLP, highlighting its essential role in phosphorus cycling under acidic conditions. In deeper soil layers, pH facilitates phosphorus mobilization from NLP pools, with effects varying across fractions. Long-term studies on Japanese Vaccinium soils reveal that pH and electrical conductivity (EC) management significantly promote NLP-to-LP conversion, primarily through NaOH-Po, thereby improving phosphorus use efficiency. These findings underscore the critical importance of prioritizing chemical property management over physical modifications to optimize nutrient cycling, preserve soil fertility, and reduce reliance on external phosphorus inputs in agricultural systems. Our study emphasizes the need for integrated approaches to achieve sustainable phosphorus management in both natural and managed ecosystems.

Mobilization and recycling of intracellular phosphorus in response to availability

Mobilization and recycling of intracellular phosphorus in response to availability

Combining sequential extractions with bulk and micro X-ray spectroscopy to elucidate iron and phosphorus speciation in sediments of an iron-treated peat lake.

In shallow lakes, mobilization of legacy phosphorus (P) from the sediments can be the main cause for persisting eutrophication after reduction of external P input. In-lake remediation measures can be applied to reduce internal P loading and to achieve ecosystem recovery. The eutrophic shallow peat lake Terra Nova (The Netherlands) was treated with iron (Fe) to enhance P retention in the sediment. This treatment, however, intensified seasonal internal P loading. An earlier study suggested that Fe addition led to increased P binding by easily-reducible Fe(III) associated with organic matter (OM), which readily releases P when bottom waters turn hypoxic. In this complementary study, bulk and micro Fe K-edge and P K-edge X-ray absorption spectroscopy and micro-focused X-ray fluorescence spectroscopy were applied to characterize the P hosting Fe(III) pool. Combined with sequential extraction data, the synchrotron X-ray analyses revealed that a continuum of co-precipitates of Fe(III) with calcium, phosphate, manganese and organic carbon within the OM matrix constitutes the reducible Fe(III) pool. The complementary analyses also shed new light on the interpretation of sequential extraction results, demonstrating that pyrite was not quantitatively extracted by nitric acid (HNO3) and that most of the Fe(II) extracted by hydrochloric acid (HCl) originated from phyllosilicate minerals. Formation of an amorphous inorganic-organic co-precipitate upon Fe addition constitutes an effective P sink in the studied peaty sediments. However, the high intrinsic reactivity of this nanoscale co-precipitate and its fine distribution in the OM matrix makes it very susceptible to reductive dissolution, leading to P remobilization under reducing conditions.

The Influence of Sanitary Infrastructure on Event Nutrient Dynamics in a Headwater Catchment

ABSTRACTMany low‐order streams are recipients of effluents from wastewater treatment plants (WWTPs) and combined sewer overflows (CSOs). Not only do these facilities have to meet fewer requirements compared to their bigger counterparts in more densely populated areas, but they also discharge into smaller, more vulnerable streams, with low dilution potential. Although these local point sources can dictate the local water quality and quantity dynamics, they are barely monitored and often not included in catchment‐wide analyses. In this case study we measured stream water quantity and quality in a first‐order, point source‐influenced stream. We have specifically addressed point sources in our monitoring programme, which included the installation of a low‐budget probe at the CSO outlet to monitor overflow timing. By clustering hysteresis loops and using Principal Component Analysis, we were able to identify hydro‐meteorological drivers and reveal seasonal patterns of discharge and nutrient export dynamics. Mobilisation of nitrate from agricultural sources clearly dominated event dynamics during periods with high soil moisture, while point source dynamics overlaid catchment responses during the rest of the time. Thus, the dilution potential of the stream was found to be a controlling factor for water quality dynamics. Groundwater infiltration into the sewer system probably increased the risk of CSO discharges, especially in winter and spring. In summer, CSO spillages occurred as a result of high‐intensity rainfall. These events were related to an increase of turbidity and a mobilisation of particulate phosphorus. With our novel approach, including urban point sources in our monitoring setup, we were able to show the close relationship between sanitary infrastructure in rural areas and stream nutrient dynamics. Including point sources more closely into monitoring and analysis is essential to improve the process understanding.

THE ROLE OF BACILLUS SPP. IN SUSTAINABLE AGRICULTURE AND BIOCONTROL

This work aims to explore the potential applications of Bacillus spp. in biological plant control and the promotion of sustainable agriculture, drawing insights from an analysis of literature data. Literature review. Plants that interact with plant growth-promoting rhizobacteria (PGPR) exhibit improved growth and enhanced resistance to stress. Among PGPR, Bacillus spp. are widely used in agriculture to boost crop yields and stress tolerance. However, their effectiveness varies under different conditions, emphasizing the need for further research to bridge the gap between laboratory and field results. Species such as Bacillus subtilis enhance nitrogen fixation, facilitate phosphorus mobilization, and increase iron uptake in plants. Additionally, Bacillus spp. produce phytohormones and other compounds that regulate the hormonal balance in plants. These bacteria protect plants from pathogens by producing antimicrobial substances such as lipopeptides and antibiotics. B. subtilis also modulates the expression of plant genes to support colonization. Biofilm formation on plant roots, regulated by quorum sensing, further promotes effective bacterial colonization. Conclusions. Studies on plant-bacteria interactions in the rhizosphere reveal that beneficial bacteria like Bacillus spp. enhance plant growth and resilience through hormone regulation, biofilm formation, modulation of plant immune responses, and improved nutrient availability and stress tolerance. B. subtilis and related species are particularly effective in increasing crop yields and combating plant diseases. Their ability to improve drought and salt tolerance is especially noteworthy, making Bacillus spp. promising candidates for sustainable agriculture.

Contrasted phosphorus mobilization strategies between upland and paddy soils: insights from phosphorus biologically factions and functional gene profiling

Contrasted phosphorus mobilization strategies between upland and paddy soils: insights from phosphorus biologically factions and functional gene profiling

Enhanced available phosphorus in paddy fields applying biochar and water-saving irrigation together: The role of alkaline phosphomonoesterase-harboring microorganisms

Organic phosphorus mineralization is one of the important pathways for phosphorus mobilization. However, the level of organic phosphorus mineralization in rice paddies under the coupling of water-saving irrigation and biochar has yet to be determined. To address this knowledge gap, we investigated the interplay between available phosphorus fractions, alkaline phosphomonoesterase activity, and bacterial communities encoding alkaline phosphomonoesterase in water-saving irrigated paddy fields subjected to different biochar applicated rates (0 t ha−1, 20 t ha−1, and 40 t ha−1), compared with a control (flooding irrigation with 0 t ha−1 biochar application). The findings revealed that changes in alkaline phosphomonoesterase activity were linked to variations in phoD gene numbers and the composition of phoD microbial communities. Water-saving irrigation, as opposed to flooding irrigation, notably enhanced the capacity of organic phosphorus mineralization in paddy fields. This enhancement was supported by a 27.94%–45.84% increase in alkaline phosphomonoesterase activity and a 23.00%–36.06% decrease in enzyme-extractable phosphorus in water-saving irrigated paddy fields vs. flooding irrigated paddy fields. Simultaneously, the important role of Firmicutes among phoD-harboring microorganism in water-saving irrigated rice paddies was detected. However, the increased capacity of microbes-mediated organic phosphorus mineralization under the condition of water-saving irrigation alone was insufficient to offset the resulting phosphorus depletion. Biochar could improve the available phosphorus content, which promoted competition among phoD-carrying microorganisms, raising the risk of phosphorus loss. The combined approach of water-saving irrigation and 40 t ha−1 biochar application enhanced the availability of phosphorus and simultaneously mitigated the risk of phosphorus loss, which is proved to be a more suitable field management strategy for paddy fields in southern China.

Modeling phosphorus transport in soil columns amended with polyaluminum chloride and anionic polyacrylamide water treatment residuals: implications for stormwater bioretention systems

ABSTRACT Understanding phosphorus transport in soil columns amended with polyaluminum chloride and anionic polyacrylamide water treatment residuals (PAC-APAM WTRs) is crucial for the effective recycling of PAC-APAM WTRs into traditional soil-based stormwater bioretention systems. Phosphorus transport in columns containing three distinct soil types amended with PAC-APAM WTRs under saturated steady-state flow conditions was effectively modeled using three different models: the convection-dispersion equation (CDE) model with linear isotherm, the CDE model with Langmuir isotherm, and the chemical non-equilibrium two-site model (TSM). In Soils 1 and 2, amended with PAC-APAM WTRs, the primary mechanism governing phosphorus transport transitioned from instantaneous adsorption to two-site adsorption as flow rate increased. In contrast, Soil 3 amended with PAC-APAM WTRs was predominantly governed by two-site adsorption throughout the experiments. An increase in flow rate reduced the solid–liquid distribution coefficient and the fraction of equilibrium adsorption sites, resulting in decreased phosphorus adsorption and increased phosphorus mobility. This study strongly recommends the selection of soil amended with PAC-APAM WTRs that exhibits higher instantaneous phosphorus adsorption. Additionally, this study emphasizes the importance of appropriately designing the depth of the ponding layer, utilizing the TSM model, and refining modeling techniques to optimize phosphorus retention and mitigate pollution risks in stormwater management.

Sedimentary geochemistry in P-limited freshwater drained marshes (Charente-Maritime, France): Original drivers for phosphorus mobilization

Phosphorus bioavailability is a major issue in aquatic environments, where it generally limits primary production. In this work, the analysis of the pore water and the solid phase of the sediment was carried out over a 9-month monitoring period between February 2020 and April 2021 in two drained marshes (Marans and Genouillé, France) distinct by their uses and management tools. Soluble reactive phosphorus (SRP) enrichment in the sediment was intimately controlled by iron oxide dissolution. The latter seemed highly controlled by seasonal nitrate inputs (winter and early spring) that favoured denitrification as a major benthic mineralization process promoting iron curtain development and stability. Following benthic mitigation of nitrate other anaerobic metabolisms developed such as iron dissolutive reduction promoting P recycling and planktic bioavailability. Surprisingly, sulphur cycle seemed to affect P dynamics, especially in the absence of nitrate. The absence of NO3− triggered high sulphate reduction rates in the two first centimeters depth, reaching −8.9 E−03 ± 0.5 E−03 and -5.0 E−03 ± 0.2 E−03 nmol cm−3 s−1 in August and July at Marans and Genouillé respectively. These values placed this process at higher rates than the denitrification (maximum in May at Marans with −5.0 E−03 ± 1.1 E−03 nmol cm−3 s−1) and reduced iron production (maximum in July at Genouillé with 0.5 E−03 ± 0.1 E−03 nmol cm−3 s−1). The rapidity with which process changes occur (monthly scale) testified to the dynamism of these systems. The similarity in geochemical patterns regarding NO3− pressure at both sites underlines the importance of diffuse pollution in coastal systems for nitrogen mitigation and phosphorus trapping. The results obtained in this study could lead to the development of a generalized diagenetic operating model for temperate systems with high agricultural pressure. This would enable to target management efforts to both optimize the purification function and limit eutrophication risks in these systems.

Potential phosphorus mobilization from riparian vegetation following freezing

Phosphorus (P) rich runoff from agricultural landscapes is a major contributor to freshwater eutrophication. Vegetated riparian zones are often employed to retain P from field runoff before it enters streams. In cold regions, vegetation has the potential to release P to runoff following freezing; however, it is unclear if this differs with winter frost severity, riparian zone local topography, vegetation type, and/or exposure to flooding/inundation. To explore the vulnerability of riparian vegetation to winter P losses, this study quantified soil and vegetation P concentrations from 8 riparian zones in Canada at different topographic positions within each riparian site (upper/field edge, lower/water edge) in both the fall and spring seasons and related this to observed surface temperatures and water levels throughout the non-growing season. This was complemented by two laboratory mesocosm experiments in which (1) plant samples were subjected to moderate (−40C) and severe (−250C) simulated winter frost treatments to quantify changes in their water extractable P (WEP) content, and (2) mesocosms were inundated with water to determine if dissolved P concentrations in flood water differed when plants were left intact, clipped but left on the soil surface, or harvested. Greater soil and vegetation P concentrations were observed at upper locations (field edge), and this remained consistent following freezing; however, vegetation WEP concentrations increased with greater simulated frost severity. In the field, temperatures were moderated by snow cover and although differences with riparian zone position were apparent between fall and spring collected samples, changes in P pools did not appear to be related to frost severity or inundation in the field. The mesocosm experiment revealed that harvesting vegetation considerably reduced dissolved P concentrations in flood water. This study shows that vegetated riparian zones can act as a source of P to streams during the winter non-growing season, and highlights the potential for riparian vegetation management in reducing P losses from riparian zones in cold climates.

Manganese(III) dominants the mobilization of phosphorus in reducing sediments: Evidence from Aha reservoir, Southwest China

Eutrophication has become one of the greatest threats to aquatic ecosystems. The release of phosphorus (P) from sediments exerts a critical role on eutrophication level. Both manganese (Mn) and iron (Fe), sensitive to redox conditions, own strong affinity for P. Numerous works have demonstrated that Fe was a key factor to drive P cycle in sediments. However, the role of Mn on P mobilization remains largely unexplored. Herein, the mechanism of P mobilization driven by Mn were investigated in a seasonal anoxic reservoir. Diffusive gradients in thin films (DGT) results, from both field investigations and laboratory incubations, showed P was synchronously distributed and significantly positive correlated (r2 ≥ 0.40, p < 0.01) with Mn, suggested that P cycle was associated with Mn. X-ray photoelectron spectroscopy (XPS) results showed that in the outer layers at the top 1 cm sediment pellet the contents of Mn and P occurred significantly synchronize changed, while that of Fe remains virtually unchanged when oxygen conditions changed. This demonstrated that Mn is likely to be the key factor affect P cycle. Most importantly, the relative content of Mn(III) changed the most (≈20 %) interpreted that Mn(III) is the key Mn species dominants the P mobilization. Furthermore, Dual-Beam scanning electron microscope (DB-SEM) maps clearly showed the co-enrichment of P and Mn in oxic sediments, confirmed P was mainly hosted by Mn minerals. In contrast, the random distributions and weak or negative correlations between P and Fe implied that P cycle was decouple with Fe, this resulted from that Fe was almost deposited as inert Fe fractions (>99.2 %) in reducing sediments. This study significantly expanded our knowledge on the geochemical behavior of P influenced by Mn in aquatic sediments.

Multimodal, microspectroscopic speciation of legacy phosphorus in two US mid‐Atlantic agricultural soils

AbstractTo understand phosphorus (P) mobility in agricultural soils and its potential environmental risk, it is essential to directly measure solid phase P speciation. Often, bulk P K‐edge X‐ray absorption near edge structure (XANES) spectroscopy followed by linear combination fitting (LCF) is utilized to determine the solid P phases in soil. However, this method may limit results to only a few major phases. Additionally, XANES spectra for different P species may have very similar features, leading to an over‐ or underestimate of their contribution to LCF. Here, an improved P speciation by pairing multimodal microbeam‐X‐ray fluorescence (µ‐XRF) mapping coupled with µ‐XANES (microbeam‐X‐ray absorption near edge structure) analysis to directly speciate major and minor P phases on the micron scale is provided. We combined maps of both tender (P, sulfur, aluminum, and silicon) and hard energy (calcium, iron [Fe], and manganese) elements to evaluate the elemental co‐locations with P. To better account for uncertainty assigning XANES peaks to individual compounds, a more quantitative fingerprinting by “spectral feature analysis” was completed. With this analysis, an R‐factor is reported for the fit. These results were compared to traditional LCF. Pre‐edge fitting results revealed the presence of a two‐component pre‐edge feature for phosphate adsorbed to ferrihydrite. Additionally, phytate co‐precipitated with ferrihydrite (Phytate‐Fe‐Cop) had a pre‐edge feature, indicating direct association with Fe. Lastly, a unique P species associated with manganese oxide was identified in the soil via multimodal mapping and µ‐XANES. These results allow for better prediction of P dissolution and mobility.

Study on Nano-Zn, Inorganic, and Organic Nutrient Management Practices and Their Impact on Nutrient Availability in Kharif Maize (Zea mays L.)

A study was conducted to assess the impact of Nano-Zn, inorganic, and organic nutrient management practices on the physico-chemical properties and nutrient availability in Kharif maize (Zea mays L.) grown during 2022 and 2023 at Chandra Shekhar Azad University of Agriculture &amp; Technology, Kanpur. The experiment followed a split-plot design, with organic manures (Control, FYM at 10 t/ha, and Vermicompost at 5 t/ha) as the main plot treatments and various nutrient management strategies (Control, 75% RDF, 75% RDF + ZnSO4 at 25 kg/ha, 75% RDF + Nano-Zn at 10 ml/litre, 100% RDF, 100% RDF + ZnSO4, and 100% RDF + Nano-Zn) as the subplot treatments. Results showed that combining 100% RDF with Nano-Zn and ZnSO4 significantly enhanced soil nutrient availability and improved physico-chemical properties compared to control treatments. The organic carbon content was highest in the 100% RDF + Nano-Zn treatment (0.492%), suggesting an increase in soil organic matter. Nitrogen availability was significantly higher in this treatment, with a pooled value of 151.167 kg/ha, compared to 143.443 kg/ha in the control. Phosphorus availability also increased in the 100% RDF + Nano-Zn treatment (16.337 kg/ha), indicating better phosphorus mobilization. Potassium availability was enhanced, with the highest recorded value (216.39 kg/ha) in the 100% RDF + Nano-Zn treatment, while the control treatment had 213.597 kg/ha. Zinc availability was markedly improved, with the 100% RDF + Nano-Zn treatment reaching 0.853 mg/kg, compared to 0.79 mg/kg in the control. This study demonstrated that integrating Nano-Zn and ZnSO4 with inorganic fertilizers significantly improved soil fertility, nutrient availability, and potentially enhanced crop performance in Kharif maize. These findings indicate that combining inorganic and nano-fertilizers could be an effective nutrient management strategy, contributing to sustainable agricultural practices and improved productivity in maize cultivation, alongside better soil health.

Mobilization of phosphorus in sediments of eutrophic lakes induced by elevated sulfate levels

Elevated sulfate levels in eutrophic lakes have been observed to induce the release of endogenous phosphorus. While previous studies have predominantly examined its impact on iron-bound phosphorus (FeP), the influence on organic phosphorus (OP), a crucial active phosphorus component in sediments, remains poorly understood. In this study, mesocosms were established with lactate supplementation and varying sulfate concentrations to explore sulfate reduction and its impacts on phosphorus mobilization in freshwater sediments. Lactate addition induced hypoxia and provided substrates, thereby stimulating sulfate reduction with a decline of sulfate levels, an increase of sulfide concentrations, and fluctuations of sulfate-reducing bacteria. Meanwhile, concentrations of total dissolved phosphorus and phosphate were dramatically promoted during lactate decomposition, with a higher sulfate concentration associated with greater phosphorus elevation, correlating with the decrease of total phosphorus in sediment. The increase in phosphorus of the overlying water was partly attributed to FeP release from the sediment, confirmed by a decrease in its sediment content. FeP release was ascribed to dissimilatory reduction of iron oxides or chemical reduction mediated by sulfides in anoxic sediments, leading to the desorption and subsequent release of phosphorus. Evidences included the proliferation of iron-reducing bacteria, a decrease in Fe(II) concentrations in sediment pore- water, and the continuous accumulation of solid iron sulfides in surface sediments. Furthermore, OP mineralization in sediment also contributed to the increase in phosphorus in water columns, confirmed by a reduction in its content and the abundance of fermentation bacteria in surface sediment. Notably, the decrease in OP content accounted for >80 % of the total phosphorus reduction in surface sediment in the end. Thus, sulfur cycling plays a critical role in iron and phosphorus cycling, significantly stimulating not only the mobilization of FeP but also OP in sediments, with OP mineralization potentially being the primary contributor to endogenous phosphorus release.

Single-cell exploration of the microbiota driving soil phosphorus mobilization.

Single-cell exploration of the microbiota driving soil phosphorus mobilization.

Effect of different microplastics on the mobilization of soil inorganic phosphorus by exomycorrhizal fungi

&lt;p&gt;Microplastics (MPs) can affect the phosphorus (P) cycle in soil by changing soil properties and the function of microbial communities, but their impact on soil P availability remains unclear. To explore the effects of different types of MPs on the mobilization of soil inorganic P by exomycorrhizal fungi, Lactarius delicious (Ld) was used as the test strain, and polystyrene microspheres (PS), polypropylene (PP) and poly(lactic acid) (PLA) were used as test materials. The soil was used as the only P source for the media. The effect of different types of MPs on the mobilization of soil inorganic P by exomycorrhizal fungi was studied using liquid culture method. The results showed that exposure to MPs at low to medium concentrations (10 or 100 mg L-1) activated inorganic P in soil by stimulating the secretion of additional organic acids and hydrogen ions by ectomycorrhizal fungi, improving the available P in soil. The effect of mobilizing inorganic P was more significant in the treatment groups exposed to low and medium concentrations of biodegradable PLA. This may be related to the fact that PLA stimulated the ectomycorrhizal fungi to secrete more organic acids, and the release of a large amount of lactic acid after PLA was biodegraded. However, when the exposure concentration of MPs further increased, the growth of ectomycorrhizal fungal mycelium may be inhibited, the secretion of organic acids and hydrogen ions may be reduced, and the mobilization ability of soil inorganic P may be limited. In addition, it should be noted that high concentrations of non biodegradable MPs (PS and PP) had significant limiting effects on the mobilization of soil inorganic P by exomycorrhizal fungi. Therefore, our study results provide evidence that the presence of MPs may reduce the availability of soil P. Further research should focus on maintaining or improving P availability in plant-microbe systems in MP-polluted soil.&lt;/p&gt;

Ten years of urea fertilization alter the pqqC‐harbouring community and increase soil inorganic phosphorus mobilization

AbstractThe bacterial communities that harbour the pyrroloquinoline quinone gene (pqqC‐harbouring bacteria communities) play a pivotal role in the mobilization of inorganic phosphorus (Pi). However, there is limited knowledge regarding the connection between soil pqqC‐harbouring bacterial communities and Pi fractions, as well as the factors that can regulate them, particularly under different fertilization strategies in the agricultural soil. High‐throughput sequencing was used to investigate the pqqC‐harbouring communities from the wheat (Triticum aestivum L.)–sweet potato (Ipomoea batatas L.) season in a 9‐year field experiment, including without fertilization (control), nitrogen (N) and potassium (K) fertilization (NK), NPK fertilization (NPK) and the combined application of chemical NPK and organic fertilizer (NPKM), and to explore their relationships with Pi fractions and their regulatory factors. Long‐term N fertilization and crop type substantially changed the community composition of pqqC‐harbouring bacteria but had no effect on their diversity. In two crop seasons, long‐term N fertilization significantly increased the content and proportion of moderately labile Pi (aluminium‐ and iron‐bound P) and available P (AP) and significantly decreased the proportion of recalcitrant Pi (calcium‐bound P) compared with the control. Specifically, AP increased by 79%–778%, Fe‐P by 64%–88%, and Al‐P by 71%–308%, while Ca‐P decreased by 10%–59%. N fertilization increased the relative abundance of Micromonospora, which was significantly positively correlated with moderately labile Pi and AP. Moreover, the relative abundance of some Streptomyces increased by 391% in the sweet potato season, and they were positively correlated with AP. Structural equation modelling revealed that the interplay between the pqqC‐harbouring community composition and Pi mobilization was mainly governed by pH, underscoring the role of pH in shaping the communities of Pi‐mobilizing microbes and their effect on Pi mobilization processes. This study emphasized how N fertilization and crops reshape Pi‐mobilizing microbial communities, which in turn affects Pi mobilization and P availability. Overall, these findings offer valuable insights into optimizing P cycles and availability through N fertilization strategies.