Biochar application under low phosphorus input promotes soil organic phosphorus mineralization by shifting bacterial phoD gene community composition

Biochar has the potential to enhance microbial-mediated phosphorus (P) cycling in soils, but the underlying mechanisms remain largely unknown. We hypothesized that biochar amendment could enhance the production of acid and alkaline phosphomonoesterase, phosphodiesterase and P mineralization, which may vary depending on the P input. To test this hypothesis, we assessed the impacts of rice straw biochar application (0 and 4%) under different P-input rates (0,30 and 90 kg P ha(-1)) on the relationships among P fractions, phosphatase activities and alkaline phosphomonoesterase-encoding bacterial (phoD gene) communities in an acidic soil. Biochar application under low P input (< 30 kg P ha(-1)) significantly increased the activities of phosphodiesterase and alkaline phosphomonoesterase but not that of acid phosphomonoesterase and depleted organic P. The results from the structural equation model revealed a dominant role of alkaline phosphomonoesterase in P mineralization. The increase in alkaline phosphomonoesterase activity was not related to an increase in phoD gene abundance but was due to a shift in community composition, which was primarily driven by the soil C:P ratio. Microbial network analysis demonstrated a more complex phoD gene community with more functionally interrelated groups as a result of biochar application under low P input than under high P input. Moreover, the specific enrichment of Micromonosporaceae under C-rich and P-poor conditions may play a critical role in alkaline phosphomonoesterase production and potential P mineralization. In conclusion, we demonstrated that biochar application under low P input supports a more organized phoD gene community and preferentially enriches taxa in terms of their capacity for P mineralization, which in turn may enhance P bioavailability and plant P acquisition. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The application of biochar under low phosphorus input conditions enhances phosphodiesterase and alkaline phosphomonoesterase activities, while reducing organic phosphorus content. The increase in alkaline phosphomonoesterase activity is not due to an increase in phoD gene abundance, but rather a shift in community composition driven by the soil C:P ratio.