Biochar application improves ammonia oxidation microbial community and increases net nitrification in vegetable soils

Objectives Ammoxidation process is a rate-limiting step of nitrification and impacts the cycling of nitrogen in soil. By analyzing the changes of soil ammonia-oxidizing microbial communities under the input of biochar to reveal the influence of biochar input on soil nitrification and the biological mechanism.

Methods We set up biochar gradient (C₀, C_0.5, C_1.5, C_4.0) soil incubation experiments in northern meadow district. PCR and T-RFLP analysis technology were used for observation of ammonia oxidizing bacterial community dynamic under biochar input soil and analysis of the relationship among biochar, soil nitrification and ammonia oxidizing bacteria.

Results The addition of biochar significantly changed the ammoxidation microbial community structure and nitrogen nitrification process. Compared with C₀, the Shannon and Evenness indices of the soil ammonia oxidizing bacteria community were increased by 5.4%–18.8%, 26.2%–33.8%, and the Shannon index were decreased by 20.7%–34.2% in late stage. The biochar input had no significant effect on the AOA community. In the community of AOB, 256 bp and 58 bp represented species abundance were increased by 61.4%–56.0%, 60.6%–78.6%, and 488 bp represented species abundance decreased by 22.8%–26.9%. 21 bp represented species abundance increase at early stage and decrease at the later stage, which was contrary to the change of 491 bp represented species abundance. In biochar added soil, the abundance of AOB amoA gene were increased by 48.9%–53.2%. The content of NO₃^–-N were increased by 1.7%–25.6%, the content of NH₄⁺-N decreased by 13.4%–31.1%, and the net nitrification rate increased by 21.8%–70.2%.

Conclusions The input of biochar improved the structure of soil ammonia-oxidizing microbial community dominated by AOB and stimulates the activity of amoA enzyme. However, it has no significant effect on the microbial community structure of ammonia-oxidizing archaea. The influence of biochar on soil net nitrification rate is closely related to the influence of biochar on soil ammonia-oxidizing bacteria community composition.