Straw alters the soil organic carbon composition and microbial community under different tillage practices in a meadow soil in Northeast China

Straw retention and tillage practices are the main ways to affect the contents and stocks of soil organic carbon (SOC) components as well as soil microbial traits in order to affect soil fertility and crop yield. Microorganisms are the links between SOC and tillage methods, but the mechanisms of these linkages remain unclear. We evaluated the changes in SOC components, soil microbial traits and crop yields under no-tillage (NT), shallow tillage (ST), deep tillage (DT), no-tillage with straw retention (NTS), shallow tillage with straw retention (STS) and deep tillage with straw retention (DTS) treatments in a 3-year field trial in a meadow soil in Northeast China. Straw retention increased the contents of both labile organic carbon (LOC, by 16.0 %) and recalcitrant organic carbon (ROC, by 19.5 %), while tillage practices increased the highly labile organic carbon (LOC-H) content from 0.4 to 0.6 g kg−1 and decreased the low-labile organic carbon (LOC-L) content from 1.6 to 0.8 g kg-1. The ANOVA and nonmetric multidimensional scaling (NMDS) results suggested that straw retention was the main factor regulating bacterial alpha diversity and reshaping the bacterial community composition. Straw retention also promoted the functions of Acidobacteria and Bacteroidetes in the network, thus influencing SOC component turnover. Structural equation modelling (SEM) revealed that the bacterial Shannon index, richness and community composition were correlated with crop yields due to their regulation of different SOC components, especially LOC-H and ROC. Overall, straw retention with no and shallow tillage increased the soil ROC and LOC contents by increasing the bacterial Shannon index and reducing the richness; thus, these practices improved crop yield, which is an important indicator of soil fertility. This study advances our understanding of the mechanisms underlying the relationships between soil microbial traits and SOC components under different straw management and tillage practices and provides information to support SOC transformation, C stock enlargement and soil fertility maintenance strategies.