Understanding the drivers and mechanisms underlying variations in autotrophic (Ra), heterotrophic (Rh), and total soil respiration (Rs) is essential for improving carbon management in croplands. In this four-year field study (2018-2021) conducted in a maize system, we compared practices without straw (NS) and with straw mulch (SM). Random Forest analysis identified bulk density, soil temperature, soil inorganic carbon, and urease activity as the primary determinants of Ra, Rh, and Rs. Straw mulch improved soil biodiversity, species richness, alpha-diversity, and evenness. Piecewise structural equation modeling further showed that soil microenvironmental changes regulate substrate availability by altering soil biological properties, which subsequently shape bacterial communities and microbial metabolism, ultimately controlling Rs. Compared with NS, on average over the fouryear study period, SM substantially enhanced Ra and Rh by 96.9% and 82.2%, respectively, and increased maize grain yield and aboveground biomass by 9.7% and 6.2%. Notably, SM shifted the net ecosystem carbon budget from negative to positive, indicating a pronounced carbon sink effect. Overall, our findings highlight the pivotal role of straw amendments in regulating Rs and its components and elucidating the pathways through which these effects occur. These results provide mechanistic evidence supporting SM as a climate-smart agricultural practice that can simultaneously enhance crop productivity and contribute to agricultural carbon sequestration strategies and carbon neutrality targets.