Resource recycling through biogas slurry topdressing reorganizes spatiotemporal dynamics of soil bacteria and carbon sequestration pathways

Organic constituents and nutrients present in biogas slurry are in a liquid state, which inevitably exert profound impacts on microbial processes and changes in environmental factors. However, existing studies have overlooked the reshaping effect of biogas slurry topdressing (BST) on the spatiotemporal dynamics of soil environmental factors and microbial communities. Based on this, this study, relying on a long-term continuous field experiment, selected three key crop growth stages and soil depths to explore the reshaping pathways and potential impacts of BST on soil microbial communities succession in agricultural ecosystems, compared with pure chemical fertilizer topdressing (CFT). Compared with CFT treatment, BST treatment consistently increased the total potassium permanganate oxidation carbon (TPOXC) content (13.44%) and soil quality index (SQI) (18.26%) across soil depths and growth phases and bacterial richness (7.83%) and diversity (1.86%) during the tasseling (VT) stage. Compared with the CFT treatment, the ratio of r/k bacterial phyla in BST treatment increased by 31.99% at the VT stage and decreased by 5.60% at the maturity stage. Additionally, BST treatment significantly enriched Firmicutes and other bacterial communities carried by the biogas slurry itself. The competitive relationship between soil environmental factors and bacterial communities in the CFT treatment was adjusted to a cooperative one in the BST treatment. Meanwhile, we propose that BST modulates the r/k strategy of bacteria by directly influencing SQI and POXC component, thereby affecting the vertical distribution and dynamic succession pathways of bacterial communities. Furthermore, BST treatment facilitated soil carbon sequestration primarily by augmenting the carbon fixation potential of the Wood-Ljungdahl and 3-Hydroxypropionate cycle pathways.