Effects of long-term fertilization on phoD-harboring bacterial community in Karst soils

Phosphorus (P) acquisition by plants from soil organic P mainly relies on microorganisms. Examining the community of functional microbes that encode phosphatases (e.g. PhoD) under different fertilization managements may provide valuable information for promoting soil organic P availability. Here, we investigated how the abundance and community diversity of phoD-harboring bacteria responded to long-term fertilization in Karst soils. Six fertilization treatments were designed as follows: non-fertilized control (CK), inorganic fertilization only (NPK), and inorganic fertilization combined with low- and high amounts of straw (LSNPK and HSNPK), or cattle manure (LMNPK and HMNPK). We found that soil available phosphorus (AP) content and the activity of alkaline phosphatase (ALP) were significantly higher in all combined inorganic/organic fertilization treatments, while the abundance of the phoD gene was only higher in the HMPNK treatment, compared to NPK. The combination of inorganic/organic fertilizations had no effect on the diversity of phoD genes compared to NPK alone, but the phoD gene richness was greater in these treatments as compared to the control. Only organic fertilization combinations with high amounts of organic matter (both HSNPK and HMNPK) significantly affected the phoD community structure. A structure equation model demonstrated that soil organic carbon (SOC), rather than P, greatly affected the phoD community structure, suggesting that organic P mineralization in soils is decoupled from C mineralization. Our results suggested that optimized combinations of inorganic/organic fertilizations could promote P availability via regulating soil phoD-harboring bacteria community diversity and ALP activity.