Response of bacterial communities to the application of sewage sludge biochar and Penicillium aculeatum in rhizosphere and bulk soil of wheat

The application of sewage sludge biochar (SSB) in agriculture is a promising solution for detoxifying and recycling the nutrient-rich sludge. However, knowledge is required on how SSB alone or in combination with biofertilizers influences the soil microbial communities. This work used a wheat pot experiment with a root free soil compartment to study effects of SSB and the phosphate-solubilizing Penicillium aculeatum on bacterial communities in wheat rhizosphere and bulk soil. Treatments were applied only to the root free soil compartment. Analysis by 16S rRNA gene amplicon sequencing showed that SSB increased the alpha diversity and induced taxon-specific shifts. These shifts occurred in both rhizosphere and bulk soil, and they were dominated by increased relative abundance of Gemmatimonadetes and Chloroflexi which were primarily explained by increases in soil P availability and soil pH, respectively. Application of P. aculeatum had smaller effects on bacterial communities and these effects occurred mainly in rhizosphere soil and were probably related to unidentified interactive rhizosphere processes. The combined application of SSB and P. aculeatum did not reveal any additive effects on the bacterial communities as compared to the sole application of SSB. Due to the different treatment effects on rhizosphere and bulk soil communities, the analysis of both soil compartments will provide a better understanding of interactions between biochar, soil, bacteria and plants.