From microbial temperature kinetics to soil carbon stocks under warming

Temperature is a major regulator of soil biogeochemistry, exerting a strong control over microbial growth and respiration, two core processes governing soil organic carbon (SOC) cycling. However, existing temperature dependence models fail to jointly describe growth and respiration, are inaccurate across the full biokinetic range, or require complex parameterisations, limiting their applicability and predictive power.

To overcome these limitations, we developed the Dual-Kinetics Ratkowsky model (Ratkowsky DK), a parsimonious framework that can simultaneously describe temperature dependences for microbial growth and respiration. Compared to established models, Ratkowsky DK shows superior performance and parsimony across soils spanning a broad climatic gradient. Despite its empirical formulation, the model provides robust estimates of microbial thermal traits and climate responsiveness, capturing warm- and cold-shifted adaptations, and offers a biologically meaningful interpretation of temperature-driven decoupling between anabolism and catabolism.

Temperature dependence models were then used to investigate the effects of warming (+5°C for 9 years) on CO₂ emissions and SOC stocks. Direct temperature effects initially increased emissions and projected substantial SOC losses, but the progressive optimisation of microbial thermal traits enhanced carbon use efficiency and reduced emissions over time, halving the projected SOC loss and closely matching observations. These findings indicate that microbial thermal trait optimisation can provide a parsimonious explanation for heat-induced carbon losses worldwide, highlighting the importance of integrating microbial dynamics into models.