Effects of long-term irrigation on soil phosphorus fractions and microbial communities in Populus euphratica...

Irrigation has been demonstrated to be effective in managing Populus euphratica plantations, but its impacts on phosphorus (P) availability and the soil microbiome have not been fully elucidated. In this study, we compared soil properties, P fractions, phosphatase activities, and microbial communities in the surface soil (0-20 cm) of P. euphratica plantations under both drought and irrigation conditions. We found that total P, labile P and moderately labile P all increased significantly under irrigation by 12.3%, 70.1%, and 3.0%, respectively. The increased levels of labile P were primarily driven by higher levels of NaHCO₃-Pi, which increased from 1.9 to 12.3 mg·kg^-1. Furthermore, irrigation markedly altered labile P composition and the relative levels of resin P, NaHCO₃-Pi, and NaHCO₃-Po were all impacted. Improved soil moisture increased soil phosphatase activity, suggesting that soil organic P (Po) mineralization was positively affected by irrigation. Moreover, we observed that bacterial diversity, fungal diversity, and alkaline phosphatase gene communities, rather than total microbial biomass carbon or total phospholipid fatty acids, were most explained in the dynamics of soil P fractions. Furthermore, we found positive correlations among inorganic P (Pi) and Bradyrhizobiaceae, Nocardiaceae, and Sphingomonadaceae, whereas negative correlations were found between Burkholderiaceae and Pi, highlighting the diverse functional bacteria involved in P cycling. Our study demonstrates that irrigation can increase soil P availability and supply capacity, with shifts in P composition closely linked to changes in soil microbial characteristics. Water management strategies that target the restoration of soil microbial communities may therefore improve soil quality and enhance soil P cycling.