Abstract: 【Objective】The objective of this study is to investigate the effects of fertilization on structure and composition of bacterial community in soybean continuous cropping in Chinese Mollisols, and the main environmental factors causing changes of bacterial communities, focusing on the analysis of the differences in the treatment of inoculated nodules. This study would provide a theoretical support for the efficient planting of soybean and the reduction of nitrogen fertilizer.【Method】Based on a 5-year fertilization experiment of soybean continuous cropping, four different fertilization treatments were sampled, including CK (no fertilizer), PK (phosphorus and potassium inorganic fertilizer), NPK (nitrogen, phosphorus and potassium inorganic fertilizer) and PK+5821 (phosphorus and potassium inorganic fertilizer with Bradyrhizobiumjaponicum 5821). High-throughput sequencing (Illumina Hiseq) and quantitative PCR of 16S rRNA gene were used to analyze bacterial communities in soil samples in different fertilization treatments. Correlation analysis of the bacterial community structure and environmental factors was followed.【Result】Compared with CK, fertilization significantly increased soybean yield and concentration of soil nutrients, it was found that single application of chemical fertilizer decreased soil pH. Inoculation with B. japonicum5821 significantly increased the gene copy number of soil bacteria, and soil bacterial abundance. The analysis of bacterial communities at phylum and class level showed that Proteobacteria, Actinobacteria and Acidobacteria were dominant bacteria, occupying more than 70% of all phyla; Fertilization significantly reduced the relative abundance of Actinobacteria in the phylum analysis, which is consistent with the level of class. Diversity analysis showed that the indexes (richness and diversity) of CK treatment were different from those in other three treatments. The principal coordinate analysis (PCoA) showed that the bacterial community structure in the 3 fertilization treatments (PK, NPK and PK+5821) clustered together on the PC1 axis, and the CK treatment was separated, which indicated that fertilization significantly changed the soil bacterial community composition. Redundancy analysis (RDA) showed that total nitrogen (F=3.2, P=0.002) had the greatest effect on the soil bacterial community structure, explaining 24% of the community changes. The order of contribution rate was total nitrogen＞available phosphorus＞available K＞organic matter＞pH. Spearman correlation analysis also showed that all the five soil physiochemical characteristics were closely related with different dominant bacteria.【Conclusion】Fertilization changed the bacterial community structure in continuous soybean cropping, and total nitrogen was the main environmental factor impacting the bacterial abundances and communities. Inoculation with B. japonicum 5821could not only significantly improve soil quality and increase soybean yield, but also reduce the application of chemical nitrogen fertilizer. This study could provide important information for the efficient planting of soybean and the reduction of nitrogenous fertilizer.

Key words: high-throughput sequencing, black soil, rhizobia, soil physiochemical characteristics, bacterial community structure