Abstract: The temperature sensitivity (Q₁₀) of soil microbial respiration (Rs) is a critical parameter for predicting the response of microbially mediated decomposition of global soil organic carbon (SOC) to climate change. However, the variations in Q₁₀ across horizontal and vertical spatial gradients remain contentious. In this study, we conducted a simulated soil warming incubation experiment across temperature gradients of 5 °C, 15 °C, 25 °C, and 35 °C using soils collected from the southern subtropical forest (SSF), mid-subtropical forest (MSF) and temperate forest (TF) in China. Soil samples were obtained from four depth intervals along a 60 cm soil profile: 0–15 cm, 15–30 cm, 30–45 cm, and 45–60 cm. We measured soil microbial respiration, SOC fractions, soil chemical properties, microbial community structure and activity. Q₁₀ values were calculated, and the underlying mechanistic relationships among these variables were examined. Significant spatial variations in Q₁₀ were observed (P < 0.05): (1) in the 30–60 cm soil layers, Q₁₀ values in TF were significantly higher than those in SSF and MSF; (2) with in SSF, Q₁₀ in the topsoil (0–15 cm) was markedly greater than that in the deep soil (45–60 cm). Horizontally, the higher Q₁₀ values in TF appear to be influenced with higher-quality carbon substrates, a greater abundance of K-strategies microbial taxa, higher microbial activity and prolonged exposure to low temperatures. Vertically, in the SSF, the higher Q₁₀ in topsoil was primarily attributed to higher SOC content, the presence of more labile carbon substrates and enhanced microbial activity. These findings underscore the important roles of carbon quality, microbial life-history strategies (K-strategies) and microbial activity in mediating the Q₁₀ of Rs, especially in deep soils which are easily ignored. Based on these findings, it can be predicted that under global warming scenarios, temperate forests may experience accelerated SOC decomposition at horizontal spatial scales, especially in deeper soil layers. In subtropical forests, topsoil may exhibit more rapid carbon loss along vertical gradients.

Key words: Temperature sensitivity (Q₁₀), Carbon quality-temperature (CQT), Microbial life-history strategies, K-strategies, Soil organic carbon decomposition