Fig. 1: Map of sample locations including soil microbial carbon use efficiency (CUE) and soil heterotrophic respiration rates in incubation conditions.

a A total of 618 samples of surface soil microbial original CUE were collected from published references with information provided on substrates added and incubation temperature. These data were strictly screened from a larger database of CUE (n = 1145), whereby the soil microbial CUE without information on substrates added and incubation temperature, with soil depths out of surface (i.e., with sampling depths > 30 cm), and measured with ¹⁸O-H₂O method were not included. b A total of 1,251 soil heterotrophic respiration measurements (μg C-CO₂ g dry-weight soil⁻¹ h⁻¹) were used from published references by Bradford et al. (n = 591) and Dacal et al. (n = 660)^5,6. The Bradford dataset was located in North America and the Dacal dataset was distributed globally. The datasets have been previously used to examine the linear thermal adaptation of heterotrophic respiration, and here we focused on examining the nonlinear thermal response of heterotrophic respiration.