Effects of biochar combined with nitrogen reduction on the soil microbial community of rapeseed

Excessive N critically depresses soil properties. Biochar has the potential to enhance soil health. A two-year field experiment was conducted to analyze the effects of biochar (0, 10, 20 and 40 t ha(-1), namely, B0, B10, B20 and B40) combined with N (180, 144 and 108 kg ha(-1), namely, N100, N80 and N60) on soil microorganisms. Results showed that B10 significantly promoted soil microbial biomass and had a strong correlation with most microbial groups, mainly reflected in a15:00, 10Me17:0, i18:0, i19:0, i16:0, 16:1w5c, 10Me18:0, 18:0 2OH and 18:00, while N60 decreased fungi and actinomycete content. Soil microbial functional activity was also significantly increased under B10 and B20 treatments and decreased under N80 and N60 treatments, compared to B0 treatment and N100 treatment, respectively. Microbial functional composition was also changed greatly by biochar, and B10 and B20 were closely related to most carbon sources. The combination of B10 and N80 significantly increased soil microbial biomass (total PLFA by 1.4 nM kg(-1)) and functional activity (Shannon index and Evenness index by 0.8%) compared with conventional N management (N100B0). Our findings reveal that biochar can achieve N reduction and enhance soil microbial diversity and community stability in purple soil regions of southwest China.