Long-Term Vineyard Cultivation Reshapes Soil Organic Phosphorus Speciation, Phosphatase Activities, and phoC- and phoD-Harboring Bacterial Communities

Organic phosphorus (OP) transformation in perennial vineyards is strongly influenced by long-term cultivation, fertilization, and associated changes in soil properties. However, the relationships among soil OP speciation, phosphatase activities, and phoC- and phoD-harboring bacterial communities remain poorly understood. In this study, soils from 20-year-old vineyards (Y20) and adjacent uncultivated reference sites (CK) in Penglai, China, were compared. Soil available P was significantly higher in Y20 than in CK, increasing from 15.83 to 40.50 mg kg−1, whereas total P, OP, and microbial biomass P did not differ significantly between treatments. The contents of soil orthophosphate and corrected monoesters (cMonoesters) were in the range of 15.34–97.45 and 6.90–24.49 mg kg−1, respectively, and were significantly higher in Y20 than in CK. Among the identified monoesters, the mean concentrations of myo-inositol hexakisphosphate (myo-IHP), scyllo-IHP, and choline phosphate in Y20 were 4.12, 0.69 and 0.69 mg kg−1, respectively, significantly higher than those observed in CK. The Y20 soils also exhibited 17.94% higher acid phosphomonoesterase (ACP) activity and 28.05% lower alkaline phosphomonoesterase (ALP) activity than the CK soils. Furthermore, the α-diversity of phoC-harboring bacteria was lower in Y20, whereas the composition of phoD-harboring communities differed significantly between the two land-use types. Correlation analyses showed that soil OP forms correlated positively with ACP activity and phoD community composition, but negatively with ALP activity. Overall, the differences between Y20 and CK suggest that long-term vineyard cultivation was associated with increased P availability through redistribution among soil P forms and with the accumulation of relatively stable cMonoesters. These patterns were closely related to phosphomonoesterase activities and the composition of phoD-harboring bacterial communities. These findings highlight the potential interactions among P speciation, phosphatase activities, and functional microbial communities in vineyard soils and provide hypotheses for further investigation of P transformation processes.