Microbial community assembly and functional potential response driven by soil phosphorus gradients

Understanding how long-term phosphorus (P) fertilization reshapes soil microbiomes and their functional interplay with P cycling is crucial for sustainable agriculture. This study investigated the effects of different P levels on soil physicochemical properties, phosphatase activities, and the bacterial community across three geographically distinct tobacco-growing sites (YD, SH, and ZS) in Fujian Province, China. Our results revealed a significant positive correlation between soil available phosphorus (AP) and phytase (R = 0.92), challenging the classical P deficiency induction paradigm. Site-specific environment was the paramount factor overriding contemporary P levels in shaping the bacterial community structure and its P-cycling genetic potential. At the broadest scale, stochastic processes dominated the assembly of regional species pools, leading to distinct community templates across sites. Within each site, however, the local P levels acted as a deterministic filter, fine-tuning community composition primarily through species replacement rather than wholesale restructuring. Functional prediction revealed site-specific P-cycling strategies: the YD community showed a higher predicted genetic potential toward aggressive P acquisition (mineralization and solubilization), whereas SH and ZS communities exhibited a higher predicted potential for P scavenging, storage, and recycling (polyphosphate degradation and transport). Redundancy analysis linked these functional profiles to distinct local soil properties: organic matter (OM) at YD, a combination of OM and multiple nutrients at SH, and potassium at ZS. In conclusion, microbial-mediated P cycling in these soils may be governed by a hierarchical mechanism: site-specific context sets the community template, localized soil properties (OM, K) shape the functional repertoire, and current P management modulates the system through species sorting and likely transcriptional regulation. This underscores the need for site-specific, ecological precision management strategies that target dominant local environmental drivers to foster microbial communities capable of optimizing soil P efficiency.