Changes of acid and alkaline phosphatase activities in long-term chemical fertilization are driven by the similar soil properties and associated microbial community composition in acidic soil

Acid and alkaline phosphatase (ACP and ALP), encoded separately by the bacterial phoC and phoD genes, participate in the mineralization of organic phosphorus (P) to inorganic P. However, the influence of chemical fertilization on soil phosphatase activities and associated bacterial communities in acidic soils remains unclear. Here, we conducted a 27 year continuous chemical fertilization experiment consisting of the no-fertilizer control (CK), N and P fertilizer (NP), N and K fertilizer (NK), P and K fertilizer (PK), and N, P and K fertilizer (NPK) treatments, in order to investigate phosphatase activities and phoC- and phoD-harboring bacterial communities. Results demonstrated that ACP and ALP activities increased significantly in the NP (198.70 and 35.46 μg pNP g−1 soil h−1, respectively) and NPK treatments (199.62 and 36.51 μg pNP g−1 soil h−1, respectively) compared to CK (143.81 and 22.49 μg pNP g−1 soil h−1, respectively), while ALP activity was reduced for the NK treatment (13.86 μg pNP g−1 soil h−1). The abundance and diversity index of phoC- and phoD-harboring bacteria differed among treatments. The two bacterial community structures exhibited similar trends in terms of the significant differences between N-free (CK and PK) and N-containing (NP, NK and NPK) treatments (Adonis, p < 0.01). Random forest model analysis revealed that the variations in ACP and ALP activities can be explained by microbial biomass P (MBP, 9.71% and 13.20%, respectively), soil total carbon (TC, 10.89% and 8.77%, respectively) and available P (AP, 9.10% and 7.15%, respectively), and microbial factors including community composition (5.94% and 4.48%, respectively) and network clustering coefficients (6.05% and 5.15%, respectively). Furthermore, the dominant genera Stenotrophomonas and Variibacter were positively correlated with ACP and ALP activities, respectively, with their members observed as keystone species in the community network. Overall, chemical N and P fertilization was generally observed to improve soil phosphatase activities in acidic soil, with soil TC and AP identified as the primary soil variables affecting phosphatase activities by altering the associated bacterial community composition and increasing MBP. These findings improve the understanding of how fertilization influences the community composition and function of phosphate-solubilizing microorganisms in acidic soils.