Crop residue decomposition plays a critical role in soil organic carbon (SOC) sequestration. However, the interactive effects of tissue-specific quality, soil moisture, and nitrogen (N) fertilization on this process remain insufficiently understood. To address this gap, we conducted a 120-day incubation experiment using 13 C-labeled maize straw tissues (stem, leaf, and sheath) to monitor residue chemical evolution and microbial community dynamics under three soil moisture levels (45%, 65%, and 90% water-holding capacity WHC) and three N addition rates (0, 24, and 36 mg N per 100 g soil). The results demonstrated that residue quality regulated decomposition patterns. Leaf residues exhibited the greatest degradation extent and SOC contribution, exceeding those of stems and sheath by 23.88–82.11% and 8.91–99.38%, respectively, attributable to their lower lignin content and higher nutrient concentrations. Soil moisture exerted tissue-dependent effects. Leaf degradation increased linearly with rising moisture, driven by enhanced leaching of labile compounds and improved substrate–microbe contact. In contrast, sheath degradation responded non-linearly, with both drought and excessive moisture promoting greater decomposition than normal moisture conditions, albeit via distinct mechanisms— K -strategist dominance under drought and physical fragmentation under waterlogging. Nitrogen effects were dose-dependent across all tissues. Low N addition (24 mg N) stimulated decomposition by alleviating microbial N limitation and increasing the fungal-to-bacterial (F/B) ratio, whereas high N addition (36 mg N) suppressed decomposition due to microbial N saturation, pH-mediated community inhibition, and lignin–N complex stabilization. Under drought conditions, low N promoted stem degradation by increasing the F/B ratio by 93.00%, thereby selecting for K -strategist decomposers, yet suppressed leaf degradation by limiting labile carbon leaching. Conversely, high N reversed this pattern, suppressing stem degradation while enhancing leaf decomposition. Under excessive moisture, low N inhibited degradation of all tissues by reducing the F/B ratio, whereas high N enhanced decomposition through increased microbial biomass and improved substrate accessibility. A mixed-effects model revealed tissue-specific driver hierarchies: moisture explained the largest proportion of variance in stem (39.97%) and leaf (45.34%) decomposition, whereas N dominated sheath decomposition (69.31%). Random forest analysis further identified G - bacteria as the primary predictor of stem carbon transformation and actinomycetes as the key predictors of leaf decomposition. These findings underscore the pivotal role of water–N–microbe interactions in regulating tissue-specific residue decomposition, with microbial community composition acting as a central driver. The results provide a mechanistic basis for developing diversified residue return strategies tailored to tissue type and local hydro-nutrient conditions, thereby enhancing soil carbon storage and promoting the sustainability of agricultural systems under changing climatic conditions. • Water–nitrogen interactions drive tissue-specific decomposition of maize residues via microbial and chemical pathways. • Under drought, low N promotes fungal decomposition of stems, while under sufficient moisture, high N enhances bacterial degradation of leaves. • Leaves exhibit the highest contribution to soil organic carbon, with carbon sequestration efficiency being regulated by the combined effects of moisture and nitrogen on microbial activity and residue chemistry.
Zhang et al. (Tue,) studied this question.