A comprehensive understanding of rice straw (RS) and biochar (BC) addition affecting soil quality, enzyme activities, bacterial community structure and grain yield is crucial. The objective of this study was to examine the dynamics of the soil microbial community impacted by the application of rice straw and biochar, and to understand the relationship between the microbial communities, soil enzymes, nutrients and grain yield of paddies. We conducted a field experiment with organic amendments under the direct seeding of paddies. The bacterial community structure in the rhizosphere was characterized using high-throughput 16S rRNA sequencing. The results showed that RS amendment increased grain yields by 8.5 and 9.9% more than with BC and the control without organic amendment (CK), respectively (p < 0.05). The abundance of bacteria associated with nitrate reduction in RS was higher than that in BC and CK, which further showed the significance of the RS-treated soil bacteria in rice nutrient utilization. A cladogram plotted using linear discriminant analysis effect size showed that Proteobacteria (Alphaproteobacteria), Acidobacteria, Firmicutes, Verrucomicrobia and Epsilonbacteraeota in the RS-treated soil increased in comparison with CK. Pearson's correlation analysis showed that enzymes activities (cellulase activity and protease activity), soil nutrition content (soil hydrolyzable nitrogen), and bacterial phyla (Nitrospinae) were positively correlated with grain yield, suggesting that the RS-treated soil improved enzyme activities, soil nutrition content, and bacterial abundance, which in turn increased grain yield. The results indicated that RS-treated bacterial communities combined with soil enzymatic activities strengthen the transformation of nutrients, suggesting that the interactions play an important role in enhancing the grain yield of paddy rice. These results provide new insights and a theoretical basis for studying the changes in soil microbial communities with the application of RS and BC in Northeastern China.
