Biochar application enhances microbial interactions in mega-aggregates of farmland black soil

Abstract Soil microbial community diversity and composition are responsive to biochar application. However, the impacts of biochar application on soil microbial community structure and interactions in different aggregate fractions are poorly understood. We conducted a 3-year field trial involving biochar application to black soil in northeastern China. Four biochar treatments were applied: 0 (B0, control), 10 (B10), 30 (B30) and 50 (B50) t ha−1 biochar. Compared to the B0 treatment, biochar application significantly decreased the diversity of bacterial and fungal communities. In addition, biochar application significantly increased the relative abundances (RAs) of Bacteroidetes and Proteobacteria and significantly decreased those of Actinobacteria, Chloroflexi, Planctomycetes and Verrucomicrobia. Moreover, the B30 and B50 treatments significantly increased and decreased the RA of Nitrospirae, respectively. Moreover, the RA trends of Acidobacteria, Nitrospirae and Planctomycetes among different aggregate fractions was mega-aggregates (ME; > 2 mm) > macroaggregates (MA; 0.25–2 mm) > microaggregates (MI;