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Soil Phosphorous (P) availability is a limiting factor for plant growth and regulates biological metabolism in plantation ecosystems. The effect of variations in soil microbial P cycling potential on the availability of soil P during succession in plantation ecosystems is unclear. In this study, a metagenomics approach was used to explore variations in the composition and diversity of microbial P genes along a 45-year recovery sequence of Robinia pseudoacacia on the Loess Plateau, as well soil properties were measured. Our results showed that the diversity of P cycling genes (inorganic P solubilization and organic P mineralization genes) increased significantly after afforestation, and the community composition showed clear differences. The gcd and ppx genes were dominant in inorganic P transformation, whereas phnM gene dominated the transformation of organic P. The abundance of genes involved in inorganic P solubilization and organic P mineralization was significantly positively correlated with P availability, particularly for phnM, gcd, ppx, and phnI genes, corresponding to the phyla Gemmatimonadetes, Acidobacteria, Bacteroidetes, and Planctomycetes. The critical drivers of the microbial main genes of soil P cycling were available P (AP) and total N (TN) in soil. Overall, these findings highlight afforestation-induced increases in microbial P cycling genes enhanced soil P availability. and help to better understand how microbial growth metabolism caused by vegetation restoration in ecologically fragile areas affects the soil P cycling.

Soil microbes have a great influence on the feedbacks of carbon (C)-climate, and their metabolic activities are limited by resource availability. Altitudinal gradients strongly affect soil microbial communities, but the effects on microbial resource limitation and their regulation for C dynamics remain unclear. In this study, we designed an altitudinal gradient experiment that included six altitudinal sites from 1308 m to 2600 m in the Qinling Mountains, China. The enzymatic stoichiometry was determined and modeled to investigate microbial resource limitations and major microbial metabolism processes (e.g., organic C decomposition rate and microbial respiration rate) along the elevation gradient. Other environmental variables including mean annual temperature (MAT) and mean annual precipitation (MAP), the C: nitrogen (N): phosphorus (P) ratio in soil total nutrients, available nutrients, and microbial biomass were also measured. The results showed that soil microbes suffered from N limitation in our study and microbial N limitation significantly increased with increasing elevation. But the rates of both organic C decomposition and microbial respiration greatly decreased with increased elevation. These trends suggest that warming induced by elevation change might relieve N limitation for microbes and lead to increased soil C release. Redundancy analysis (RDA) showed that MAT and soil nutrient stoichiometry, particularly for the DOC: TDN ratio, explained more variations for changes in microbial N limitation and major microbial processes. Collectively, our study demonstrated that the higher microbial N limitation at high elevation may be beneficial to soil carbon accumulation by changing the C: N ratio, which provided insights into microbially mediated soil carbon release under global warming.