Effects of biochar addition on the microbial diversity of paddy soils under fertilizer reduction

We studied the effects of rice straw biochar addition on the microbial diversity of a paddy soil under fertilizer reduction. The MiSeq high-throughput sequencing analysis technology was used to analyze the microbial diversity of the rhizosphere and bulk soil under different levels of fertilization application（100%, 90%, and 80% of the conventional fertilization）and rice straw biochar addition（1%）. The results indicated that the microbial diversity of the rhizosphere was more abundant than that of the bulk soil. Proteobacteria was the dominant phylum of Gram-negative bacteria accounting for 34.85%~47.57%. Biochar addition could reduce the abundance of Proteobacteria in the bulk soil and promote it in the rhizosphere. However, the reduction of fertilizer had an opposite effect on the abundance of Proteobacteria, while the greater influence was evidenced with more fertilizer reduction. In addition, Acidobacteria accounted for 10.48%~19.42%, which had an opposite response to that of Proteobacteria. At the genus level, Unclassified Burkholderiaceae, Unclassified Subgroup 6, and Unclassified bacterium 126 accounted for a relatively high proportion or microorganisms in the rhizosphere and bulk soil. The results of the Canonical Correspondence Analysis（CCA）showed that the abundance of dominant bacteria was related to environmental factors such as sampling location, fertilizer treatment, and biochar addition. Our study showed that the different fertilizer reduction（80% or 90%）and rice straw biochar addition（1%）could influence the microbial diversity of the rhizosphere and bulk soil, which was closely related to sampling location, fertilizer reduction, and biochar addition.