Partitioning biochar properties to elucidate their contributions to bacterial and fungal community composition of purple soil.

Although effects of biochar application on soil microorganism have been increasingly reported, the direct evidences for demonstrating the contributions of biochar chemical and physical properties to soil microorganisms are still lacking. Herein, we partitioned corn-straw biochar (BC) into three fractions, including aqueous extractable substances (AE), organic extractable substances (OE) and the remaining solid (EBC) after these two extractions. These fractions and BC were added to purple soil for a 30-day incubation. Soil properties, microbial α-diversity indices and microbial community compositions were analysed after the incubation. The results showed the obvious changes in soil properties, along with higher available P, available K and total organic C, as well as, lower pH and available N than those of soil without biochar, were observed in the BC-treated soil. Illumina Miseq sequencing displayed a distinct difference between responses of bacteria and fungi to biochar application, in which fungal richness and diversity were increased, and no significant changes happened in bacterial richness. Furthermore, biochar had apparent effects on bacterial and fungal community compositions at phylum level, which were most close to the influences of AE and EBC, respectively. These results suggested that AE, improving soil nutrients (e.g., total N), played a pivotal role in changing bacterial phylum community composition. The EBC, regarded as physical structure and relatively recalcitrant compounds of BC, had a dominant contribution to the influence of biochar on the fungal community composition.