Coupled Temperature Sensitivity of Microbial Carbon and Nitrogen Use Efficiencies in Forest Soils on a Continental Scale

Microbial carbon and nitrogen use efficiencies (CUE and NUE) are critical regulators of soil carbon and nitrogen cycling, with their temperature sensitivities playing a pivotal role in mediating biogeochemical feedbacks under global warming. However, how the temperature sensitivity (Q₁₀) of CUE and NUE varies at different temperature ranges and whether their thermal responses are coordinated remains poorly understood. Here, we quantified the Q₁₀ of CUE and NUE in 55 soil samples collected from a ~4000 km latitudinal forest transect in eastern China. We further identified key drivers that shaped Q₁₀ variability from climatic, edaphic, and microbial factors. On average, Q₁₀ was 1.22 ± 0.08 for CUE and 1.46 ± 0.13 for NUE. However, both efficiencies exhibited clear temperature-interval dependence: the mean Q₁₀ of CUE declined from 1.47 ± 0.14 at 12°C-20°C to 0.97 ± 0.08 at 20°C-28°C, while the mean Q₁₀ of NUE decreased from 2.00 ± 0.23 to 0.93 ± 0.09. The Q₁₀ values of CUE and NUE were strongly correlated across temperature ranges and positively associated with the Q₁₀ of microbial growth, indicating a coordinated thermal response governed primarily by growth-based processes. At lower incubation temperature interval (12°C-20°C), variation in the Q₁₀ of CUE was primarily explained by soil stoichiometry and microbial community attributes, whereas under warmer conditions (20°C-28°C), climatic and edaphic constraints, particularly precipitation and soil N/P ratio, became dominant. Although microbial community attributes consistently explained most of the variance in the Q₁₀ of NUE, their influence weakened at higher incubation temperatures, paralleling the pattern observed for CUE and indicating a shift from biotic to abiotic control. Overall, these findings highlight that the temperature sensitivities of microbial CUE and NUE are tightly coupled, growth-mediated, and strongly temperature-context dependent, providing novel insights for improving predictions of soil carbon-nitrogen turnover under climate warming.