The shift of bacterial community composition magnifies over time in response to different sources of soybean residues

© 2019 The Authors The transformation of plant residues by soil microorganisms contributes significantly to soil carbon (C) sequestration. Although the contribution of different soybean residue sources (leaf, stalk and root) to soil organic C have been quantified in the highly productive Mollisols, the temporal dynamics of microbial community composition during the transformation has not. This study examined the effect of the soybean residues and incubation time on the bacterial community in a Mollisol during 150 days of incubation. Compared to the non-residue control, the presence of soybean residues increased abundances of Bacteroidetes, Actinobacteria and Firmicutes, but decreased those of Proteobacteria and Acidobacteria 15 days after residue amendment. The bacterial community composition differed between the residue sources after 60 days of incubation with the abundance of Niastella increasing in the leaf (from 4.5% to 19.1%) and stalk (from 6.5% to 25.7%) but not root treatments. The abundance of Bacillus significantly decreased in the stalk (from 12.2% to 2.2%) and root (from 4.0% to 1.6%) but not leaf-residue treatments. The abundance of bacterial genera was significantly associated with soil chemical variables including soil C, N, and pH. Overall, chemical variables drove the temporal response of the bacterial community succession, which provides insight into bacterial contribution to C turnover in soils.