Fig. 3: Nonlinear thermal response of soil microbial carbon usage efficiency (CUE) is linked or partially contributed by soil heterotrophic respiration.

Partial feature contributions of MAT to heterotrophic respiration rate at a standard incubation temperature (natural log-transformed, μg C-CO₂ g dry-weight soil⁻¹ h⁻¹) in global Dacal et al. (2019)⁵ (a) and regional Bradford et al. (2019)⁶ (b) datasets after controlling for effects of microbial biomass, substrates, incubation temperature, and soil properties. The percent of variance explained increased from 59% and 67% by multivariate linear regression in the original studies^5,6 to 75% and 91%, respectively, when using the Random Forest machine learning algorithm in this study. Microbial biomass is included in the analysis to represent the heterotrophic respiration rates at a controlled biomass.