Plastic film mulching often increases the yield of winter wheat in the Loess Plateau of China, but the physiological mechanisms are unclear, especially in response to the interaction between mulch and water supply. In this study, we investigated the interactive effects of initial soil water (dry, moderate, and wet), soil cover (plastic mulch, bare soil), and seasonal conditions on the dynamics of dry matter partitioning, water-soluble carbohydrates (WSC), and flag leaf senescence, and their relations with yield and its components. Plastic mulch increased dry matter accumulation at anthesis and maturity relative to bare soil, with no interaction with season or initial soil water. Allocation of dry matter to leaf, stem, and spike did not change with soil cover. Compared with bare soil, mulch increased WSC accumulation by 14% at anthesis and its translocation by 16%. Soil cover did not influence the senescence of flag leaf after anthesis as indicated by similar dynamics of the C:N ratio. Grain yield was higher under plastic mulch than bare soil in two out of three seasons, and was associated with a higher translocation amount of WSC and post-anthesis dry matter that linked grain weight, grain number, and harvest index.

Mitigating climate change necessitates a thorough understanding of soil organic carbon (SOC) decomposition and its response to warming. The overuse of synthetic fertilizers can alter SOC composition and affect carbon cycling, potentially changing the temperature sensitivity (Q₁₀) of SOC decomposition. This study evaluated the Q₁₀ of SOC decomposition after long-term (37-year) excessive fertilization in a loess soil. Four treatments were compared: control (no nutrient input, CK); recommended rates of synthetic nitrogen (N) and phosphorus (P) fertilizers (CF_r); excessive rates of N and P fertilizers (CF_h); and CF_h plus organic manure (MCF_h). The Q₁₀ of SOC decomposition was investigated via an incubation experiment at temperatures of 15 °C, 25 °C and 35 °C within 63 days. Compared with CF_r, long-term CF_h and MCF_h significantly increased SOC contents by 14% and 67%, and this increase was driven primarily by rises in mineral-associated organic carbon (MOC) of 28% and 62% and particulate organic carbon (POC) of 32% and 79%, respectively, under CF_h and MCF_h. While CF_h and MCF_h did not change the SOC composition, they increased the proportions of fine POC (fPOC) to SOC by 10% and 91%, and the ratio of light POC to SOC by 78% and 143%, respectively. Q₁₀ values ranged from 2.18 to 3.00 across all treatments, with a mean of 2.64. Both CF_h and MCF_h drastically enhanced the Q₁₀ values by 38% and 25% compared with CF_r at 15–25 °C. However, MCF_h significantly decreased the Q₁₀ value by 31% relative to CF_r at 25–35 °C. Partial least squares path modeling showed that soil physicochemical properties and labile carbon fractions differed significantly among treatments, with physical properties regulating labile carbon fractions. Fertilization significantly increased the Q₁₀ value at 15–25 °C owing to increased proportion of labile carbon fractions and decreased labile carbon content. Our results suggest that SOC gains from continuous addition of synthetic fertilizers are vulnerable to loss under warming. However, this loss could be alleviated by incorporation of organic manure. Thus, integration of organic manure into nutrient management practices could be an efficient way to counteract warming-induced SOC decomposition.