Phosphorus depletion in forest soils shapes bacterial communities towards phosphorus recycling systems

Different microbial functional traits drive bulk and rhizosphere soil phosphorus mobilization in an alpine meadow after nitrogen input

Enhanced nitrogen (N) input is expected to influence the soil phosphorus (P) cycling through biotic and abiotic factors. Among these factors, soil microorganisms play a vital role in regulating soil P availability. However, the divergent contribution of functional microorganisms to soil P availability in the rhizosphere and bulk soil under N addition remains unclear. We conducted an N addition experiment with four N input rates (0, 5, 10, and 15 g N m-2 year-1) in an alpine meadow over three years. Metagenomics was employed to investigate the functional microbial traits in the rhizosphere and bulk soil. We showed that N addition had positive effects on microbial functional traits related to P-cycling in the bulk and rhizosphere soil. Specifically, high N addition significantly increased the abundance of most microbial genes in the bulk soil but only enhanced the abundance of five genes in the rhizosphere soil. The soil compartment, rather than the N addition treatment, was the dominant factor explaining the changes in the diversity and network of functional microorganisms. Furthermore, the abundance of functional microbial genes had a profound effect on soil available P, particularly in bulk soil P availability driven by the ppa and ppx genes, as well as rhizosphere soil P availability driven by the ugpE gene. Our results highlight that N addition stimulates the microbial potential for soil P mobilization in alpine meadows. Distinct microbial genes play vital roles in soil P availability in bulk and rhizosphere soil respectively. This indicates the necessity for models to further our knowledge of P mobilization processes from the bulk soil to the rhizosphere soil, allowing for more precise predictions of the effects of N enrichment on soil P cycling.

Phosphorus starvation response genes and function coupling: A mechanism to regulate phosphorus availability in a subtropical estuary

Phosphorus (P) plays an important role in regulating primary production in estuarine environments. However, knowledge of the P-functional gene composition of microbial communities and the mechanisms of microbial adaptation to changes in available P in estuaries remain limited. This study coupling 16 s rDNA and metagenomics sequencing was conducted to reveal the relationship between P cycling functional genes, microbial interactions, and P availability in the Jiulong River Estuary. The results showed that the relative abundance of P cycling functions genes was highest in winter, and lowest in summer. Spatially, the total relative abundance of P cycling functions genes was higher in the riverward than that in the seaward. P cycling functional microbial interactions and P cycling gene coupling were strongest in summer and in the seaward. Changes in both temperature and salinity had significant direct and indirect effects on P cycling function, and the influence of salinity on P cycling function was greater than that on the microbial community in the estuary. Salinity had significant direct negative effects on inorganic P-solubilization (IP), organic P-mineralization (OP), and P uptake and transport functions (PT). Whereas, salinity had a significant positive effect on P-starvation response regulation (PR) function. Thus, salinity and microbial communities regulate the soluble reactive phosphate concentrations in estuarine environments by strengthening internal coupling among P cycling functions, promoting PR function, and facilitating PT gene expression. PR is the most important predictors, PR, PT, and PR-PT together explained 38.56 % of the overall soluble reactive phosphorus (SRP) variation. Over 66 % of the explained SRP variations can be predicted by the PR, PT, and PR-PT functional genes. This finding improves the knowledge base of the microbial processes for P cycling and provides a foundation for eutrophication management strategies in the estuary.

Green manure incorporation enhanced soil labile phosphorus and fruit tree growth

Introduction

The incorporation of green manures substantially enhances the conversion of external phosphorus (P) fertilizers and soil-reserved P into forms readily available to plants. The study aims to evaluate the influence of green manure additions on soil phosphorus dynamics and citrus growth, considering different green manure species and initial soil phosphorus levels. Additionally, the research seeks to elucidate the microbiological mechanisms underlying the observed effects.

Methods

A citrus pot experiment was conducted under both P-surplus (1.50 g·P·kg-1) and P-deficient (0.17 g·P·kg-1) soils with incorporating legume (Leg), non-legume (Non-Leg) or no green manure residues (CK), and 18O-P labeled KH2PO4 (0.5 g, containing 80‰ δ18Op) was additionally introduced to trace the turnover characteristics of chemical P fertilizer mediated by soil microorganisms.

Results and discussion

In P-surplus soil, compared with the CK treatment, the Leg treatment significantly increased soil H2O-Pi (13.6%), NaHCO3-Po (8.9%), NaOH-Pi (9.5%) and NaOH-Po (30.0%) content. It also promoted rapid turnover of P sources into H2O-Pi and NaHCO3-Pi pools by enhancing the phoC (576.6%) gene abundance. In contrast, the Non-Leg treatment significantly augmented soil H2O-Pi (9.2%) and NaHCO3-Po (8.5%) content, facilitating the turnover of P sources into NaHCO3-Pi pools. Under P-deficient soil conditions, compared with the CK treatment, the Leg treatment notably raised soil H2O-Pi (150.0%), NaHCO3-Pi (66.3%), NaHCO3-Po (34.8%) and NaOH-Pi (59.0%) content, contributing to the transfer of P sources into NaHCO3-Pi and NaOH-Pi pools. This effect was achieved through elevated ALP (33.8%) and ACP (12.9%) activities and increased pqqC (48.1%), phoC (42.9%), phoD (21.7%), and bpp (27.4%) gene abundances. The Non-Leg treatment, on the other hand, led to significant increases in soil NaHCO3-Pi (299.0%) and NaHCO3-Po (132.6%) content, thereby facilitating the turnover of P sources into NaHCO3-Pi and NaOH-Pi pools, except for the phoC gene abundance. Both Leg and Non-Leg treatments significantly improved citrus growth (7.3-20.0%) and P uptake (15.4-42.1%) in P-deficient soil but yielded no substantial effects in P-surplus soil. In summary, introducing green manure crops, particularly legume green manure, emerges as a valuable approach to enhance soil P availability and foster fruit tree growth in orchard production.

Penicillium oxalicum augments soil lead immobilization by affecting indigenous microbial community structure and inorganic phosphate solubilization potential during microbial-induced phosphate precipitation

Phosphate-solubilizing microorganisms (PSMs) are critically important for increasing soil phosphate (P) and decreasing lead (Pb) bioavailability during microbial-induced phosphate precipitation (MIPP). However, their relative contributions to the indigenous soil microbial communities and P-cycling genes during the MIPP process remain unclear. In this study, inoculation of the PSM P. oxalicum in hydroxyapatite-cultured and Pb-contaminated soil increased soil phosphatase activities, available P (AP) concentrations and reduced available Pb levels. Metagenomics revealed a 3.9-44.0% increase in the abundance of P-cycling genes by P. oxalicum inoculation. No P-cycling genes were assigned to Penicillium. While P. oxalicum increased the complexity of microbial community co-occurrence networks, and improved the directly interrelationships between Penicillium and genera containing P-cycling gene. These results suggesting that P. oxalicum obviously positively affected the regulation of indigenous P-cycling functional communities during the MIPP process. Inorganic P solubilization genes (gcd, ppa, and ppx) have been shown to affect soil AP, suggesting that inorganic P solubilization is the major driver of Pb immobilization improvement following P. oxalicum inoculation. These results enhance our understanding of the significant ecological role of PSMs in governing soil P-cycling and alleviating Pb²⁺ biotoxicity during the MIPP process.

Effects of Polyethylene Microplastics and Phenanthrene on Soil Properties, Enzyme Activities and Bacterial Communities

Microplastics (MPs) or polycyclic aromatic hydrocarbons (PAHs) pollution has received increasing concern due to their ubiquitous distribution and potential risks in soils. However, nothing is known about the influences of PAHs-MPs combined pollution on soil ecosystems. To address the knowledge gap, a 1-year soil microcosm experiment was conducted to systematically investigate the single and combined effect of polyethylene (PE) /phenanthrene (PHE) on soil chemical properties, enzymatic activities and bacterial communities (i.e., diversity, composition and function). Results showed that PE and PHE-PE significantly decreased soil pH. The available phosphorus (AP) and neutral phosphatase activity were not considerably changed by PHE, PE and PHE-PE. Significant enhancement of dehydrogenase activity in a PHE-PE amended system might be due to the degradation of PHE by indigenous bacteria (i.e., Sphingomonas, Sphingobium), and PE could enhance this stimulative effect. PHE and PHE-PE led to a slight increase in soil organic matter (SOM) and fluorescein diacetate hydrolase (FDAse) activity but a decrease in available nitrogen (AN) and urease activity. PE significantly enhanced the functions of nitrogen cycle and metabolism, reducing SOM/AN contents but increasing urease/FDAse activities. There were insignificant impacts on overall community diversity and composition in treated samples, although some bacterial genera were significantly stimulated or attenuated with treatments. In conclusion, the addition of PHE and PE influenced the soil chemical properties, enzymatic activities and bacterial community diversity/composition to some extent. The significantly positive effect of PE on the nitrogen cycle and on metabolic function might lead to the conspicuous alterations in SOM/AN contents and urease/FDAse activities. This study may provide new basic information for understanding the ecological risk of PAHs-MPs combined pollution in soils.

Different mechanisms driving increasing abundance of microbial phosphorus cycling gene groups along an elevational gradient

Microbes play an integral role in forest soil phosphorus (P) cycling. However, the variation of microbial P-cycling functional genes and their controlling factors in forest soils is unclearly. We used metagenomics to investigate changes in the abundance of genes involved in P-starvation response regulation, P-uptake and transport, and P-solubilization and mineralization along the five elevational gradients. Our results showed the abundance of three P cycling gene groups increasing along the elevational gradient. Acidobacteria and Proteobacteria were the dominant microbial phyla determining the turnover of soil P-solubilization and immobilization. Along the elevational gradient, soil substrates are the major factor explaining variation in P-starvation response regulation genes. Soil environment is the main driver of P-uptake and transport and P-solubilization and mineralization genes. This study provided insights into the regulation of P-cycling from a microbial functional profile perspective, highlighting the importance of substrate and environmental factors for P-cycling genes in forest soils.

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P-cycling functional genes increased along the elevational gradient

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Acidobacteria and Proteobacteria are the key phyla for P cycle in forest soils

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Microbial functional gene groups for P-cycling were driven by different factors

Biotransformation of Tris(2-chloroethyl) Phosphate (TCEP) in Sediment Microcosms and the Adaptation of Microbial Communities to TCEP

Tris(2-chloroethyl) phosphate (TCEP), a typical chlorinated organophosphate ester (OPE), is an emerging contaminant of global concern because of its frequent occurrence, potential toxic effects, and persistence in the environment. In this study, we investigated the microbial TCEP biotransformation and the development of microbial communities in sediment microcosms with repeated TCEP amendments. The TCEP degradation fitted pseudo-zero-order kinetics, with reaction rates of 0.068 mg/(L h) after the first spike of 5 mg/L and 1.85 mg/(L h) after the second spike of 50 mg/L. TCEP was mainly degraded via phosphoester bond hydrolysis, evidenced by the production of bis(2-chloroethyl) phosphate (BCEP) and mono-chloroethyl phosphate (MCEP). Bis(2-chloroethyl) 2-hydroxyethyl phosphate (TCEP-OH), phosphoric bis(2-chloroethyl) (2-oxoethyl) ester (TCEP-CHO), phosphoric acid bis(2-chloroethyl)(carboxymethyl) ester (TCEP-COOH), and 2-chloroethyl 2-hydroxyethyl hydrogen phosphate (BCEP-OH) were also identified as microbial TCEP transformation products, indicating that TCEP degradation may follow hydrolytic dechlorination and oxidation pathways. Microbial community compositions in TCEP-amended microcosms shifted away from control microcosms after the second TCEP spike. Burkholderiales and Rhizobiales were two prevalent bacterial guilds enriched in TCEP-amended microcosms and were linked to the higher abundances of alkaline and acid phosphatase genes and genes involved in the metabolism of 2-chloroethanol, a side product of TCEP hydrolysis, indicating their importance in degrading TCEP and its metabolites.

Response of soil enzyme activities and bacterial communities to the accumulation of microplastics in an acid cropped soil

The ecological stress of microplastics (MPs) contamination in agroecosystems raise worldwide concerns. However very few studies concentrated on the effects of MPs exposure on soil microbial community. The alterations of enzymatic activities and bacterial communities were assayed by spiking 1% and 5% (w/w) of polyethylene (PE) and polyvinyl chloride (PVC) MPs in an acid soil. The results showed that both PE and PVC addition inhibited fluorescein diacetate hydrolase activity and stimulated urease and acid phosphatase activities, and declined the richness and diversity of the bacterial communities. More severe effects were observed in the PE treated soils compared to the PVC treated soils generally. The relative abundances of families Burkholderiaceae increased significantly (p < .05) after MPs addition, suggesting the bacteria associated with nitrogen fixation stimulated by the MPs input. Meanwhile, significant (p < .05) decline of Sphingomonadaceae and Xanthobacteraceae after addition of 5% PVC and 1% PE MPs, respectively implied that MPs might inhibit the biodegradation of xenobiotics in the soil. Mover, the PICRUSt analysis demonstrated that membrane transporter was a sensitive prediction functional gene of microplastics exposure in the soil. Future studies could be focused on the role of MPs on the regulation of nitrogen cycling and organic compounds degradation in soils.