Accelerated microbial turnover but constant growth efficiency with warming in soil

Whether rising temperatures will reduce global soil carbon stocks and enhance climate warming remains uncertain, in part because of a poor understanding of the mechanisms of soil microbial response to warming. Research now shows that microbial growth efficiency is insensitive to temperature change and that the response of microbial respiration to warming is driven by accelerated microbial turnover and enzyme kinetics. Rising temperatures are expected to reduce global soil carbon (C) stocks, driving a positive feedback to climate change1,2,3. However, the mechanisms underlying this prediction are not well understood, including how temperature affects microbial enzyme kinetics, growth efficiency (MGE), and turnover4,5. 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 warming6,7,8, 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.