Biochar application regulates organic phosphorus fractions and the release of available phosphorus in farmland soil.

BACKGROUND: The relationship between phosphorus (P) related enzymatic activity and organic P turnover remains unclear, particularly in the context of biochar application. Field experiments were conducted on Phaeozem and Luvisol soil types to investigate the effects of biochar application rates - 0 t ha-1 (CK), 22.5 t ha-1 (D1), 67.5 t ha-1 (D2), and 112.5 t ha-1 (D3) - on soil organic fractions using 31P nuclear magnetic resonance (NMR) spectroscopy and relevant phosphatase activity. RESULTS: The application of biochar increased the soil organic carbon (SOC), pyrophosphate (pyro), and orthophosphate (ortho) content, as well as the acid phosphomonoesterase (AcP), alkaline phosphomonoesterase (AlP), inorganic pyrophosphatase (IPP), and phosphodiesterase (PD) activities. Biochar application also increased soil organic P (OPa), the sum of inorganic P forms (IP), ortho, monoesters, and myo-IHP contents, the pH value, AlP and PD activities in Phaeozem, but it significantly reduced diesters, polyphosphate (poly) contents, and IPP and AcP activities compared to those in Luvisol. Acid phosphomonoesterase and PD activities also showed an opposite trend in Luvisol. The structural equation model showed that the potential mechanism of organic P turnover in response to biochar application differed depending on the soil types, potentially influenced by P availability. CONCLUSION: Overall, the findings of this study enhance the comprehension of the variation of P fractions and their availability in the context of biochar application for agricultural production in northeastern China. © 2024 Society of Chemical Industry.

Extraradical hyphae alleviate nitrogen deposition-induced phosphorus deficiency in ectomycorrhiza-dominated forests.

The continuous imbalance between nitrogen (N) and phosphorus (P) deposition is expected to shift many ecosystems from N- to P limitation. Extraradical hyphae of ectomycorrhizal (ECM) fungi play important roles in plant nutrient acquisition under nutrient deficiency. However, whether and how ECM hyphae enhance soil P availability to alleviate N-induced P deficiency remains unclear. We investigated the impacts of ECM hyphae on transformations among different soil P fractions and underlying mechanisms under N deposition in two ECM-dominated forests. Ectomycorrhizal hyphae enhanced soil P availability under N addition by stimulating mineralization of organic P (Po) and desorption and solubilization of secondary mineral P, as indicated by N-induced increase in positive hyphal effect on plant-available P pool and negative hyphal effects on Po and secondary mineral P pools. Moreover, ECM hyphae increased soil phosphatase activity and abundance of microbial genes associated with Po mineralization and inorganic P solubilization, while decreasing concentrations of Fe/Al oxides. Our results suggest that ECM hyphae can alleviate N-induced P deficiency in ECM-dominated forests by regulating interactions between microbial and abiotic factors involved in soil P transformations. This advances our understanding of plant acclimation strategies via mediating plant-mycorrhiza interactions to sustain forest production and functional stability under changing environments.

Resiliencies of soil phosphorus fractions after natural summer fire are governed by microbial activity and cation availability in a semi-arid Inceptisol.

The unintended impact of natural summer fire on soil is complicated and rather less studied than its above-ground impact. Recognising the impact of a fire on silvopastoral soils and their resilience can aid in improving the management of silvopastoral systems. We studied the immediate (after 1 week (W)) and short-term (after 3 months (M)) recovery of different soil biological and chemical properties after the natural fire, with specific emphasis on phosphorus (P) dynamics. Soil samples were collected from four different layers (0-15, 15-30, 30-45, and 45-60 cm) of Morus alba, Leucaena leucocephala, and Ficus infectoria based silvopastoral systems. In the 0-15 cm soil layer, soil organic carbon (SOC) declined by ∼37, 42, and 30% after the fire in Morus-, Leucaena-, and Ficus-based systems, respectively within 1W of fire. However, after 3M of fire, Morus and Leucaena regained ∼6 and 11.5% SOC as compared to their status after 1W in the 0-15 cm soil layer. After 1W of the fire, soil nitrogen (N), sulfur (S), and potassium availability declined significantly at 0-15 cm soil layer in all systems. Iron and manganese availability improved significantly after 1W of the fire. Saloid bound P and aluminium bound P declined significantly immediately after the fire, increasing availability in all systems. However, calcium bound P did not change significantly after the fire. Dehydrogenase and alkaline phosphatase activity declined significantly after the fire, however, phenol oxidase and peroxidase activity were unaltered. Resiliencies of these soil properties were significantly impacted by soil depth and time. Path analysis indicated microbial activity and cationic micronutrients majorly governed the resilience of soil P fractions and P availability. Pasture yield was not significantly improved after the fire, so natural summer fire must be prevented to avoid loss of SOC, N, and S.

Effects of different mulching and fertilization on phosphorus transformation in upland farmland.

In the present study, the impact of different soil surface mulching, fertilization on phosphorus mineralization and bio-availability of spring maize at various growth stages and soil layers (0-20 and 20-40 cm soil layer) were evaluated. The results indicated that the contents of total P and Olsen-Phosphorus (Olsen-P) in the soils of 0-20 cm soil layer were significantly higher than those in the 20-40 cm soil layer at different stages. The addition of organic fertilizer significantly increased the soil total P and Olsen-P content in the 0-20 cm soil layer. The different surface mulching, no mulching (NM), gravel mulching (GM) and film mulching (FM) were significantly affected by the content of Olsen-P in both soil layers during the critical growth period of spring maize. The Ca10-P contents in both soil layers were the maximum in terms of the inorganic phosphorus content in soils with different surface mulching and different fertilization. Surface mulching significantly affected the transformation of inorganic phosphorus in different soil layers of dry-land farmland, and accelerated the increase of Ca2-P content (first phosphorus source) in 0-20 cm soil layer by GM and FM. In addition, phosphorus combined with inorganic nitrogen fertilizer increased Ca8-P (second Olsen-P source) to a certain extent, and reduced the relative content of Ca2-P (first phosphorus source). Compared with phosphate (P), nitrogen and phosphorus (NP) treatments, manure and nitrogen and phosphorus (MNP) treatments increased the contents of Ca2-P (first phosphorus source) and Ca8-P (second effective phosphorus source), while it reduced the insoluble phosphorus source (O-P) content.

Organophosphorus mineralizing-Streptomyces species underpins uranate immobilization and phosphorus availability in uranium tailings.

Phosphate-solubilizing bacteria (PSB) are important but often overlooked regulators of uranium (U) cycling in soil. However, the impact of PSB on uranate fixation coupled with the decomposition of recalcitrant phosphorus (P) in mining land remains poorly understood. Here, we combined gene amplicon sequencing, metagenome and metatranscriptome sequencing analysis and strain isolation to explore the effects of PSB on the stabilization of uranate and P availability in U mining areas. We found that the content of available phosphorus (AP), carbonate-U and Fe-Mn-U oxides in tailings was significantly (P < 0.05) higher than their adjacent soils. Also, organic phosphate mineralizing (PhoD) bacteria (e.g., Streptomyces) and inorganic phosphate solubilizing (gcd) bacteria (e.g., Rhodococcus) were enriched in tailings and soils, but only organic phosphate mineralizing-bacteria substantially contributed to the AP. Notably, most genes involved in organophosphorus mineralization and uranate resistance were widely present in tailings rather than soil. Comparative genomics analyses supported that organophosphorus mineralizing-Streptomyces species could increase soil AP content and immobilize U(VI) through organophosphorus mineralization (e.g., PhoD, ugpBAEC) and U resistance related genes (e.g., petA). We further demonstrated that the isolated Streptomyces sp. PSBY1 could enhance the U(VI) immobilization mediated by the NADH-dependent ubiquinol-cytochrome c reductase (petA) through decomposing organophosphorous compounds. This study advances our understanding of the roles of PSB in regulating the fixation of uranate and P availability in U tailings.

Enhancing simultaneous nitrogen and phosphorus availability through biochar addition during Chinese medicinal herbal residues composting: Synergism of microbes and humus.

The disposal of Chinese medicinal herbal residues (CMHRs) derived from Chinese medicine extraction poses a significant environmental challenge. Aerobic composting presents a sustainable treatment method, yet optimizing nutrient conversion remains a critical concern. This study investigated the effect and mechanism of biochar addition on nitrogen and phosphorus transformation to enhance the efficacy and quality of compost products. The findings reveal that incorporating biochar considerably enhanced the process of nutrient conversion. Specifically, biochar addition promoted the retention of bioavailable organic nitrogen and reduced nitrogen loss by 28.1 %. Meanwhile, adding biochar inhibited the conversion of available phosphorus to non-available phosphorus while enhancing its conversion to moderately available phosphorus, thereby preserving phosphorus availability post-composting. Furthermore, the inclusion of biochar altered microbial community structure and fostered organic matter retention and humus formation, ultimately affecting the modification of nitrogen and phosphorus forms. Structural equation modeling revealed that microbial community had a more pronounced impact on bioavailable organic nitrogen, while humic acid exerted a more significant effect on phosphorus availability. This research provides a viable approach and foundation for regulating the levels of nitrogen and phosphorus nutrients during composting, serving as a valuable reference for the development of sustainable utilization technologies pertaining to CMHRs.

Practical strategies of phosphorus reclamation from sewage sludge after different thermal processing: Insights into phosphorus transformation.

In the context of circular economy and global shortage of phosphorus (P) fertilizer production, it is crucial to effectively recover P during the treatment and disposal of sewage sludge (SS). Although thermal treatment of SS has been widely applied, a targeted P reclamation route is not yet well established. This study has comprehensively investigated and compared the physicochemical properties of SS and solid residues (hydrochar (HC), biochar (BC), sewage sludge ash (SSA), hydrochar ash (HCA), and biochar ash (BCA)) after application of three typical thermal treatment techniques (i.e., hydrothermal carbonization (180‒240 °C), pyrolysis (400‒600 °C) and combustion (850 ℃). P speciation and transformation during thermal processes were extensively explored followed by a rational proposal of effective P reclamation routes. Specifically, thermal processing decomposed organic P and converted non-apatite P to apatite P. Orthophosphate-P was found to be the main species in all samples. Physicochemical properties of the resulting thermal-derived products were significantly affected by the thermal techniques applied, thereby determining their feasibility for different P reclamation purposes. In particular, ash is not recommended for agricultural use due to higher harmful metals content, while acid leaching can be an alternative solution to synthesize non-Fe-containing P products because of the lower co-dissolved Fe content in the leachate. HC and BC offer the option for synthesis of Fe containing products. Eventually, HC and BC demonstrate great potential for agriculture application, however, a comprehensive risk assessment should be conducted before their real-world applications.

Migration of phosphorus in pig manure during pyrolysis process and slow-release mechanism of biochar in hydroponic application.

Pyrolysis is an effective method for treating of livestock and poultry manure developed in recent years. It can completely decompose pathogens and antibiotics, stabilize heavy metals, and enrich phosphorus (P) in biochar. To elucidate the P migration mechanism under different pig manure pyrolysis temperatures, sequential fractionation, solution 31P nuclear magnetic resonance, X-ray photoelectron spectroscopy, X-ray diffraction, and K-edge X-ray absorption near-edge structure techniques were used to analyze the P species in pig manure biochar (PMB). The results indicated that most of the organic P in the pig manure was converted to inorganic P during pyrolysis. Moreover, the transformation to different P groups pathways was clarified. The phase transition from amorphous to crystalline calcium phosphate was promoted when the temperature was above 600 °C. The content of P extracted by hydrochloric acid, which was the long-term available P for plant uptake, increased significantly. PMB pyrolyzed at 600 °C can be used as a highly effective substitute for P source. It provides the necessary P species (e.g. water-soluble P.) and metal elements for the growth of water spinach plants, and which are slow-release comparing with the Hogland nutrient solution.

Changes in the transformation of nitrogen and phosphorus under different microbial communities in sewage pipes.

Microbial communities living in different environments can affect the transformation of nitrogen and phosphorus in sewage pipes. Two different environments were simulated to investigate the differences in the transformation of nitrogen and phosphorus under different microbial communities in the pipe. Results showed that the concentration of nitrogen and phosphorus changed greatly in the first 25-33 days and the first 21 days, respectively, and then remained stable. The decrease in amino acid nitrogen (AAN) concentration and the increase in ammonia nitrogen (NH4 + -N) concentration in the sediments were evident in the contrast group. The concentrations of total phosphorus (TP), dissolved total phosphorus (DTP), and dissolved reactive phosphorus (DRP) in the overlying water and interstitial water decreased, and that of TP in the sediment increased. Some microorganisms in the sediments of both groups are related to the transformation of nitrogen and phosphorus, such as Clostridium_sensu_stricto_1, Sporacetigenium, Norank_f__Anaerolineaceae, Norank_f__norank_o__PeM15, and Caldisericum. The relative abundance of these microorganisms was remarkably differed between the two groups, which partly caused the difference in nitrogen and phosphorus transformation among overlying water, interstitial water, and sediment in the two environments. PRACTITIONER POINTS: The concentration of N and P changed greatly in the first 20-30 days. AAN and NH4 + -N in sediments had greater concentration variation in contrast group. In two groups, TP, DTP, and DRP of water decreased, and TP of sediment increased. Microbe related to the transformation of N and P differed between the two groups.

Deciphering the crop-soil-enzyme C:N:P stoichiometry nexus: A 5-year study on manure-induced changes in soil phosphorus transformation and release risk.

Carbon:nitrogen:phosphorus (C:N:P) stoichiometry plays a vital role in regulating P transformation in agriculture ecosystems. However, the impact of balanced C:N:P stoichiometry in paddy soil, particularly regarding relative soil P transformation, remains unknown. This study explores the response of C:N:P stoichiometry to manure substitution and its regulatory role in soil P transformation, along with the associated release risk to the environment. Based on a 5-year field study, our findings reveal that replacing 30 % of chemical P fertilizer with pig manure (equal total NPK amounts with chemical P fertilizer treatment, named CFM) increased soil total C without altering soil total P, resulting in an elevated soil C:P ratio, despite the homeostasis of crop stoichiometry. This increase promoted microbial diversity and the accumulation of organic P in the soil. The Proteobacteria and Actinobacteria produced lower C:PEEA metabolism together, and enhanced in vivo turnover of P. Additionally, by integrating high-resolution dialysis (HR-Peeper), diffusive gradients in thin films (DGT), DGT-induced fluxes in the soil (DIFS), and sediment P release risk index (SPRRI) models, we observed that, in addition to organic P, CFM simultaneously increased soil Al-P, thereby weakening the diffusion and resupply capacity of P from soil solids to the solution. Consequently, this decrease in P release risk to the environment was demonstrated. Overall, this study establishes a connection between crop-soil-enzyme C:N:P stoichiometry, soil microorganisms, and soil P biogeochemical processes. The study further evaluates the P release risk to the environment, providing a novel perspective on both the direct and indirect effects of manure substitution on soil P cycling.

Genomics and metabolic characteristics of simultaneous heterotrophic nitrification aerobic denitrification and aerobic phosphorus removal by Acinetobacter indicus CZH-5.

This study provides for the first time a systematic understanding of Acinetobacter indicus CZH-5 performance, metabolic pathway and genomic characteristics for aerobic nitrogen (N) and phosphorus (P) removal. Acinetobacter indicus CZH-5 showed promising performance in heterotrophic nitrification aerobic denitrification and aerobic phosphorus removal. Under optimal conditions, the maximum ammonia-N, total nitrogen and orthophosphate-P removal efficiencies were 90.17%, 86.33%, and 99.89%, respectively. The wide tolerance range suggests the strong environmental adaptability of the bacteria. The complete genome of this strain was reconstructed. Whole genome annotation was used to re-construct the N and P metabolic pathways, and related intracellular substance metabolic pathways were proposed. The transcription levels of related functional genes and enzyme activities further confirmed these metabolic mechanisms. N removal was achieved via the nitrification-denitrification pathway. Furthermore, CZH-5 exhibited significant aerobic P uptake, with phosphate diesters as the main species of intracellular P.

Slow release of attapulgite based nano-enabled glyphosate improves soil phosphatase activity, organic P-pool and proliferation of dominant bacterial community.

Glyphosate (Glp) was encapsulated onto the dopamine-modified attapulgite to develop an attapulgite-based nano-enabled Glp (DGlp) in this study with comparable weed control effects to pure Glp and commercial Glp solutions. Within 24 hours, the active Glp molecule was slowly released from DGlp at a maximum remaining rate of over 90%, and then degraded similarly to Glp solution in soil. The addition of DGlp improved soil available phosphorus (P) contents, phosphatase activity, and enzyme extractable P fraction. However, compared to Glp solution, DGlp addition had no effect on the transformation of soil inorganic P fractions. The 16S rRNA sequencing and co-occurrence network results revealed that DGlp had no significant effect on the soil bacterial diversity but diminished the complexity of soil bacterial network. According to the Mantel test, DGlp addition stimulated soil phosphatase activity and proliferation of dominant bacterial taxa (Proteobacteria and Firmicutes) capable of degrading Glp. Proteobacteria and Firmicutes that had been extensively recruited and enriched for their phosphatase activities may have mobilized reactive enzyme-P, significantly enhancing the transformation of reactive organic P and P-pool in soil. These results contributed to our understanding of the ecotoxicity and environmental impacts of nano-enabled Glp prior to its successful and sustainable application in agriculture.

Transformation trend of nitrogen and phosphorus in the sediment of the sewage pipeline and their distribution along the pipeline.

Microorganisms transform nitrogen and phosphorus in the sediment of sewage pipelines. When the sediment was scoured by water flow, these elements migrate. This work studied the changes in biofilm morphology and microbial community structure, and focused on the differences in the transformation of nitrogen and phosphorus along the pipeline. The results showed that the nitrogen and phosphorus concentrations varied systematically with time and space (the front, middle, and posterior segments of the pipe). With time, amino acid nitrogen (AAN) concentration in the sediment gradually decreased, NH4+-N concentration slowly increased, NO3--N concentration began to increase after 25 days, and TP concentration continued to increase after 9 days. The AAN, NH4+-N, and TP concentrations were highest in the posterior segment of the pipe and lowest in the front segment. However, NO3--N showed two stages: its concentration was highest in the front segment and lowest in the posterior segment during the first 17 days, after which the opposite was observed. Changes in the nitrogen and phosphorus concentrations were related to the microbial communities in the sediments. The abundances of Rhodobacter (0.001

[Functional Genomics Analysis of Nitrogen and Phosphorus Transformation in Maize Rhizosphere Microorganisms].

Fertilizer reduction and efficiency improvement is an important basis for ensuring the safety of the agricultural ecological environment. Microorganisms are the key driving force for regulating the soil nitrogen and phosphorus cycle. Studying the nitrogen and phosphorus transformation function of rhizosphere microorganisms can provide a microbiological regulation approach for further improving the use efficiency of soil nitrogen and phosphorus. Based on the field micro-plot experiments of three typical farmland soils(phaeozem, cambisol, and acrisol), metagenomic sequencing technology was used to study the differences in functional genes and regulatory factors of maize rhizosphere microorganisms during soil nitrogen and phosphorus transformation. The results showed that the functional diversity of maize rhizosphere microorganisms was affected by soil type. The functional diversity of rhizosphere microorganisms in phaeozem and cambisol was mainly affected by water content and nutrient content, and that in acrisol was affected by total phosphorus(TP) and available phosphorus(AP). For soil nitrogen transformation, the gene abundance of related enzymes in the pathway of nitrogen transformation was the highest in the urease gene(ureC) and glucose dehydrogenase gene(gdh), which were 7.25×10-5-12.88×10-5 and 4.47×10-5-7.49×10-5, respectively. The total abundance of assimilatory nitrate reduction functional genes in acrisol was higher than that in phaeozem and cambisol, and the total abundance of functional genes related to other processes was the highest in cambisol. The abundance of functional genes encoding enzymes related to nitrogen metabolism was mainly driven by soil bacterial richness, total potassium(TK), and TP. For soil phosphorus transformation, the number of alkaline phosphatase genes(phoD) catalyzing organic phosphorus mineralization was 1093, and the number of acid phosphatase genes(PHO) was 42. The abundance of phoD was two orders of magnitude higher than that of PHO. In addition, fertilization had no significant effect on the abundance of phoD and PHO in the same soil type. Random forest analysis showed that the abundances of phoD and PHO were significantly affected by soil moisture, organic matter(OM), and total nitrogen(TN), but AP content had the greatest impact on PHO abundance. These results clarified the nitrogen and phosphorus transformation characteristics of maize rhizosphere microorganisms at the functional genomic level and enriched the molecular biological mechanism of the microbial nitrogen and phosphorus transformation function.

Crop fertilisation potential of phosphorus in hydrochars produced from sewage sludge.

Sewage sludges are a rich underused source of phosphorus (P) which contributes to environmental degradation, yet if recaptured, could return significant amounts of P to agricultural systems. Hydrothermal carbonisation (HTC) can efficiently recover P, with the added ability to transform P species into potentially more desirable forms for direct application to crops. P dynamics in hydrochars have primarily examined P speciation and chemical extractability as indicators of P bioavailability, but few studies directly evaluate the agronomic effectiveness of hydrochars as P fertilisers. As such, there is a clear need to assess the suitability of hydrochar as a source of bioavailable P in plant systems and the influence of HTC synthesis conditions. Response Surface Modelling of HTC synthesis conditions (pH, temperature and time), revealed initial pH significantly influence P distribution. Mild conditions of 180 °C for 30 min at pH 8.0 maximised P recovery (99%) along with carbon (62%) and nitrogen (43%) in hydrochars. Systematic characterisation of hydrochar P by chemical extraction and P L2,3-edge X-ray absorption near edge spectroscopy revealed H2O, NaHCO3 and NaOH- P fractions were significantly (p < 0.05) reduced in all hydrochars, while HCl-P fraction increased with HTC temperatures at pH 7. In contrast, P L2,3-edge XANES spectra were remarkably similar in raw sludges and corresponding hydrochars, regardless of HTC temperature or pH, revealing P was predominantly present as ferric phosphate with some hydroxyapatite. Multiple linear regression modelling suggested a significant relationship between chemical extractability and P bioavailability to wheat present in the raw sludges and hydrochars. This research provides further insight into the potential to use hydrothermal treatment for recovery and agricultural reuse of P, the importance of operational conditions on P transformation and the relationship between P speciation and bioavailability. The value of sewage sludge in a more sustainable global P cycle is also highlighted.

Insights into enzyme activity and phosphorus conversion during kitchen waste composting utilizing phosphorus-solubilizing bacterial inoculation.

The main objective of this research was to investigate the effects of Phosphorus-Solubilizing Bacterial (PSB) inoculant on the bacterial structure and phosphorus transformation during kitchen waste composting. High throughput sequencing, topological roles, and multiple analysis methods were conducted to explain the links between phosphorus fractions, enzyme contents, and microbial community structure and function. The findings indicated that bacterial inoculant improved environmental parameters and increased the concentration of total phosphorus, Olsen phosphorus, citric acid phosphorus, OM decomposition, and bacterial diversity. Network analysis concluded that the inoculation treatment was more complex (nodes and edges) and contained more positive links than the control, implying the inoculation effect. The structural equation model also displayed that pH and enzyme activity directly enhanced the phosphorus conversion and bacterial structure. Overall, these results suggest that bacterial inoculation may considerably increase enzyme activity, thus improving biological phosphorus transformation and nutrient content in composting products.

Animal manures promoted soil phosphorus transformation via affecting soil microbial community in paddy soil.

Animal manures are reported as good substitutes for chemical fertilizers to mobilize soil phosphorus (P). However, the mechanisms on how different types of manures regulate microbial biomass involved in P mobilization remain unclear. In this study, we conducted a two-year field experiment to investigate variations in soil microbial biomass carbon (MBC) and P (MBP) and P fractions after 30% animal manures substitution (pig manure (PM), chicken manure (CM), and dairy manure (DM)) in paddy soil. Furthermore, a 30-day incubation experiment was used to explore the mechanisms of soil P transformation induced by 100% manures addition. Two-year field experiment results showed that, compared to the chemical NPK fertilizer, 30% manure substitution didn't influence rice and wheat yields significantly but decreased soil total P loss from runoff by 3.2%. However, 30% manure substitution significantly enhanced MBC and MBP by 11.3-18.4% and 57.1-81.2%, respectively, which also promoted the transformation of moderately labile P (M-P) to labile P (L-P). Moreover, the incubation experiment also convinced that all manures caused higher MBC than chemical P fertilizer. Meanwhile, compared to the no P fertilizer, manures increased L-P and organic P by 2.7%-14.7% and 6.4%-20.0%, respectively. Redundancy analysis indicated that soil MBC/MBP ratio was the main factor to soil L-P and M-P, indicating that animal manures can improve soil microbial abundance and thus promote M-P to L-P in soil. Among three animal manures, PM could improve the mobilization potential of P mostly, due to the highest C source activity by 13C NMR analysis. Our study indicated that animal manures especially PM can be considered as a good candidate for agricultural P management in paddy soils because of their capacity to promote soil P transformation.

Distribution of Culturable Phosphate-Solubilizing Bacteria in Soil Aggregates and Their Potential for Phosphorus Acquisition.

Deciphering distribution patterns of phosphate-solubilizing bacteria (PSB) and phosphorus-cycling-related genes in soils is important to evaluate phosphorus (P) transformation. However, the linkage between PSB number and P-cycling-related gene abundance in soils, especially soil aggregates, remains largely unknown. Here, we estimated the numbers of PSB and abundances of P-cycling-related genes (i.e., gcd and bpp) in soil aggregates under different fertilization regimes as well as P-solubilizing performance and plant-growth-promoting ability of PSB. We found that tricalcium phosphate-solubilizing bacteria, phytate-degrading bacteria, and gcd and bpp abundances were more abundant in silt plus clay (silt+clay; <53 µm) than in macroaggregate (250 to 2000 µm) and microaggregate (53 to 250 µm). Fertilization treatment and aggregate fractionation showed distinct effects on PSB number and P-cycling-related gene abundance. We found significantly negative correlation between gcd gene abundance and tricalcium phosphate-solubilizing bacterial number (Col-CaP) and dramatically positive correlation between bpp gene abundance and phytate-degrading bacterial number (Col-Phy). P fractions were responsible for PSB number and P-cycling-related gene abundance. The isolated Pseudomonas sp. strain PSB-2 and Arthrobacter sp. strain PSB-5 exhibited good performances for solubilizing tricalcium phosphate. The inoculation of Pseudomonas sp. PSB-2 could significantly enhance plant fresh weight, plant dry weight, and plant height. Our results emphasized distinct distribution characteristics of PSB and P-cycling-related genes in soil aggregates and deciphered a close linkage between PSB number and P-cycling-related gene abundance. Our findings might guide the isolation of PSB from agricultural soils and provide a candidate plant-growth-promoting bacterium for agro-ecosystems. IMPORTANCE Phosphate-solubilizing bacteria are responsible for inorganic P solubilization and organic P mineralization. Elucidating the linkage between phosphate-solubilizing bacterial number and P-cycling-related gene abundance is important to isolate plant-growth-promoting bacteria for agro-ecosystems. Our findings reveal differentiating strategies of phosphate-solubilizing bacteria in soil aggregates, and the deciphered P fractions show strong effects on distribution patterns of phosphate-solubilizing bacteria and P-cycling-related genes. Additionally, we isolated phosphate-solubilizing bacteria with good plant-growth-promoting ability. This study enriches our knowledge of P cycling in soil aggregates and might guide the production and management of farmland.

Effects of consecutive culture of Penaeus vannamei on phosphorus transformation and microbial community in sediment.

Phosphorus (P) is highly related to water quality during shrimp culture. Recognizing P transformation in pond-based cultures is crucial for sustainable and healthy aquaculture. However, P transformation remains unclear in the sediment of Penaeus vannamei cultures, although commercial species have been pervasive worldwide. To determine P transformation, samples with different culture years were collected from Zhejiang province, China. Sequential chemical extraction was applied to reveal the composition of inorganic P, while phosphatase activity was used to evaluate the biomineralization of organic P. The results indicated that the consecutive culture of Penaeus vannamei promoted the dissolution potential of sedimentary P. This was attributed to anoxic iron reduction that increased the formation of loosely bound P and Fe (II)-P. However, this phenomenon was dominated by biomineralization, which transformed the organic P to inorganic P. The results suggested that consecutive culture changed the microbial community structure in the sediment as well as the gene functions. The Shannon Wiener index showed that increasing the culture duration significantly decreased the stability of the microbial community. Overall, this study suggests that long-term consecutive culture of Penaeus vannamei may increase the P release potential of the sediment, which increases the risk of pond eutrophication.

Drought promotes soil phosphorus transformation and reduces phosphorus bioavailability in a temperate forest.

Drought can substantially alter ecosystem functions, especially biogeochemical cycles of key nutrients. As an essential but often limiting nutrient, P plays a central role in critical ecosystem processes (i.e. primary productivity). However, little is known about how drought can affect the soil phosphorus (P) cycle and its bioavailability in forest ecosystems. Here, we conducted a four-year field drought experiment using throughfall reduction approach to examine how drought can alter soil P dynamics and bioavailability in a warm temperate forest. We found that the P held in calcium phosphate was significantly decreased under drought, which was accompanied by the increases of inorganic and organic P bound with secondary minerals (Fe/Al oxides). These drought-induced P transformations can be well explained by the soil pH. The significant decline in soil pH under drought can drive the solubilization of P held in calcium phosphate. Our study further showed that drought directly decreased soil P bioavailability and altered the potential mechanisms of the replenishment of inorganic P into the soil solution. The potential of the inorganic P release driven by protons was reduced, while inorganic P release potentials driven by enzyme and organic acid were increased under drought. Therefore, our results strongly suggested that drought can significantly alter the soil P biogeochemical cycles and change the biological mechanisms underlying P bioavailability.