Accelerated microbial turnover but constant growth efficiency with warming in soil

Rising temperatures are expected to reduce global soil carbon (C) stocks, driving a positive feedback to climate change^{1, 2, 3}. However, the mechanisms underlying this prediction are not well understood, including how temperature affects microbial enzyme kinetics, growth efficiency (MGE), and turnover^{4, 5}. Here, in a laboratory study, we show that microbial turnover accelerates with warming and, along with enzyme kinetics, determines the response of microbial respiration to temperature change. In contrast, MGE, which is generally thought to decline with warming^{6, 7, 8}, showed no temperature sensitivity. A microbial-enzyme model suggests that such temperature sensitive microbial turnover would promote soil C accumulation with warming, in contrast to reduced soil C predicted by traditional biogeochemical models. Furthermore, the effect of increased microbial turnover differs from the effects of reduced MGE, causing larger increases in soil C stocks. Our results demonstrate that the response of soil C to warming is affected by changes in microbial turnover. This control should be included in the next generation of models to improve prediction of soil C feedbacks to warming.