Biogas slurry strategy reshapes biochar-mediated greenhouse gas emissions via soil bacterial sub-communities

Abstract Biochar addition (BA) has been considered a promising strategy for mitigating soil greenhouse gas (GHG) emissions. However, it is essential to assess whether the benefits are retained under different water and fertilizer strategies (WFSs), particularly under the biogas slurry strategy (BSS), and the specific effects of different BA ratios on GHG emissions must also be assessed. This study examined the effects of two WFSs on soil GHGs emissions and bacterial sub-communities under different BA ratios and investigated their potential mechanisms using soil column experiments. Under the conventional chemical fertilizer strategy (CFS), BA reduced CO 2 emissions by 29.19–36.51%, but simultaneously increased CH 4 emissions by 21.62–135.08% and N 2 O emissions by 48.16–51.31%. Transitioning from CFS to BSS led to a 14.89% reduction in CO 2 emissions and a 71.83% reduction in N 2 O emissions, whereas the CH 4 emissions increased by 101.72%. Concurrently, BA concentrations of 4% and 6% intensified the modulatory effect of BSS on these GHGs, whereas a 2% BA concentration had an opposing regulatory effect. Both BSS and BA were also found to enhance the abundance of rare bacterial sub-communities within the soil. Furthermore, this study revealed that BSS reshaped the GHG emission pathway regulated by BA through bacterial sub-communities, emphasizing the ''priority effect'' of these communities in controlling GHG emissions. This study has also highlighted the integral role of carbon and nitrogen turnover processes within bacterial sub-communities for the regulation of GHGs emissions. In conclusion, this study demonstrates that the effectiveness of BA in reducing soil GHGs emissions depends on the WFS. Graphical Abstract