Microbial regulation of phosphorus cycling under soil amendments and shrub selection in arid limestone mine...

Phosphorus (P) limitation constrains ecological restoration in arid limestone mine regions, where inorganic P is predominantly present in recalcitrant forms. We examined whether soil amendments and drought-tolerant shrub species are associated with shifts in inorganic phosphorus (IP) fractions through modifications of soil properties and microbial community structure during early-stage restoration. A field experiment combining four substrate amendment strategies and seven drought-tolerant shrub species was conducted under microsite-based planting conditions in degraded calcareous soils. Our results demonstrate that organic amendments increased available P by 10.73% relative to the control and were associated with higher soil water content (SWC) and microbial biomass. Partial least squares structural equation modeling (PLS-SEM) revealed that SWC was positively associated with labile P (LP), whereas microbial biomass indicators showed statistical associations with recalcitrant P (RP) pools. Microbial community analyses revealed that Actinobacteriota and Bacteroidota were significantly correlated with LP and RP fractions, while Proteobacteria were linked to moderate-cycling P (MP), suggesting potential functional differentiation among microbial groups. We therefore propose a conceptual framework of "functional specialization-dynamic equilibrium", in which soil physicochemical conditions and microbial community composition jointly influence IP distribution patterns at the microsite scale. These findings highlight how localized amendment strategies and shrub selection may contribute to improving P availability during early restoration stages, while longer-term and multi-season validation is required to assess temporal stability and field-scale generalizability.