Linking temperature sensitivity of soil CO₂ release to substrate, environmental, and microbial properties across alpine ecosystems

Our knowledge of fundamental drivers of the temperature sensitivity (Q₁₀) of soil carbon dioxide (CO₂) release is crucial for improving the predictability of soil carbon dynamics in Earth System Models. However, patterns and determinants of Q₁₀ over a broad geographic scale are not fully understood, especially in alpine ecosystems. Here we addressed this issue by incubating surface soils (0–10 cm) obtained from 156 sites across Tibetan alpine grasslands. Q₁₀ was estimated from the dynamics of the soil CO₂ release rate under varying temperatures of 5–25°C. Structure equation modeling was performed to evaluate the relative importance of substrate, environmental, and microbial properties in regulating the soil CO₂ release rate and Q₁₀. Our results indicated that steppe soils had significantly lower CO₂ release rates but higher Q₁₀ than meadow soils. The combination of substrate properties and environmental variables could predict 52% of the variation in soil CO₂ release rate across all grassland sites and explained 37% and 58% of the variation in Q₁₀ across the steppe and meadow sites, respectively. Of these, precipitation was the best predictor of soil CO₂ release rate. Basal microbial respiration rate (B) was the most important predictor of Q₁₀ in steppe soils, whereas soil pH outweighed B as the major regulator in meadow soils. These results demonstrate that carbon quality and environmental variables coregulate Q₁₀ across alpine ecosystems, implying that modelers can rely on the “carbon-quality temperature” hypothesis for estimating apparent temperature sensitivities, but relevant environmental factors, especially soil pH, should be considered in higher-productivity alpine regions.