Oxalic Acid Enhances Soil Microbial Phosphorus Mobilization Under Phosphorus Deficiency: Evidence from a Soil Microcosm Experiment

Oxalic acid is a key root exudate released by plants under phosphorus (P) deficiency and plays a direct role in solubilizing fixed soil P. However, its specific effects on soil microbial community assembly and ecological functions remain less clear. In this study, based on an ex planta soil microcosm incubation experiment, the impacts of oxalic acid input on soil bacterial and fungal community assemblage and functional profiles involved in P mobilization were explored. The results showed that oxalic acid input significantly changed soil bacterial and fungal community composition, decreased their diversity, and enriched bacterial taxa involved in P mobilization and fungal taxa associated with plants, showing the selective effects of oxalic acid on soil microorganisms. Further community assembly analyses (βNTI and NST) showed that oxalic acid input promoted a shift in bacterial community from a stochastic-process-dominated community to a deterministic-process-dominated community, while the fungal community exhibited a converse pattern. These findings reveal the important role of oxalic acid in shaping soil microbial community assembly and ecological functions under P deficiency, broadening our understanding of the role of oxalic acid in plant responses to low-P stress.