Altered microbial P cycling genes drive P availability in soil after afforestation.

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.

Changes in Soil Organic C Fractions and C Pool Stability Are Mediated by C-Degrading Enzymes in Litter Decomposition of Robinia pseudoacacia Plantations.

Litter decomposition is the main source of soil organic carbon (SOC) pool, regarding as an important part of terrestrial ecosystem C dynamics. The turnover of SOC is mainly regulated by extracellular enzymes secreted by microorganisms. However, the response mechanism of soil C-degrading enzymes and SOC in litter decomposition remains unclear. To clarify how SOC fraction dynamics respond to C-degrading enzymes in litter decomposition, we used field experiments to collect leaf litter and SOC fractions from the underlying layer in Robinia pseudoacacia plantations on the Loess Plateau. Our results showed that SOC, easily oxidizable organic C, dissolved organic C, and microbial biomass C increased significantly during the decomposition process. Litter decomposition significantly decreased soil hydrolase activity, but slightly increased oxidase activity. Correlation analysis results showed that SOC fractions were significantly positively correlated with the litter mass, lignin, soil moisture, and oxidase activity, but significantly negatively correlated with cellulose content and soil pH. Partial least squares path models revealed that soil C-degrading enzymes can directly or indirectly affect the changes of soil C fractions. The most direct factors affecting the SOC fractions of topsoil during litter decomposition were litter lignin and cellulose degradation, soil pH, and C-degrading enzymes. Furthermore, regression analysis showed that the decrease of SOC stability in litter decomposition was closely related to the decrease of soil hydrolase to oxidase ratio. These results highlighted that litter degradation-induced changes in C-degrading enzyme activity significantly affected SOC fractions. Furthermore, the distribution of soil hydrolases and oxidases affected the stability of SOC during litter decomposition. These findings provided a theoretical framework for a more comprehensive understanding of C turnover and stabilization mechanisms between plant and soil.