High throughput sequencing analysis of biogeographical distribution of bacterial communities in the black soils of northeast China

Black soils (Mollisols) are one of the most important soil resources for maintaining food security of China and are mainly distributed in northeast China. To understand which environmental factors influence the microbial communities and how the communities are distributed in the black soils, we collected 26 soil samples with different soil carbon contents across the black soil zone in northeast China, and the soil bacterial community compositions were estimated using high resolution bar-coded pyrosequencing. A total of 355,813 bacterial 16S rDNA sequences were obtained, which were classified into at least 35 bacterial groups. The dominant groups across all samples (>5% of all sequences) were Acidobacteria, Actinobacteria, Proteobacteria, Bacteroidetes, Chloroflexi, Gemmatimonadetes and Planctomycetes. The composition and diversity of the soil bacterial community were dominantly affected by both soil pH and soil total carbon content, and the effect of soil pH was stronger than that of soil carbon content. Variance partitioning analysis showed that geographic distance contributed 14.75% of the bacterial community variation, and soil environmental factors explained approximately 37.52% of the variation. Pairwise analysis showed that a relatively higher diversity of the bacterial community was observed at lower latitudes, suggesting that a latitudinal diversity gradient of the bacterial community might be present in the black soil zone. In general, our results indicated that contemporary factors, such as soil pH and soil carbon content, were more important than the historical factor of geographic distance in shaping the bacterial community in the black soil zone in northeast China.