Grow-C · Tracing microbial carbon allocation to growth and survival strategies in soil

Soil is Earth’s largest organic carbon reservoir. A small shift in soil organic carbon (SOC) can profoundly impact global climate. At the heart of these processes are soil heterotrophic microbes, whose C allocation is a fundamental yet poorly quantified driver of SOC dynamics. Current studies focus almost exclusively on C allocated to replicative growth (cell division), overlooking two essential non-replicative growth processes: the synthesis of intracellular storage compounds (ISC) and extracellular polymeric substances (EPS). These processes are vital for microbial survival under environmental stress and can account for up to 3% of SOC. Critically, no method currently exists to simultaneously measure in situ C allocated to these processes, limiting our ability to predict their contribution to SOC dynamics. This is where Grow-C steps in. Grow-C will uncover in situ microbial C allocation patterns and how they shift under environmental stress and adapt to long-term climate change. It will pioneer a water-based stable isotope probing (D2O-SIP) method to quantify, for the first time, in situ rate-based C allocation to replicative growth, ISC, and EPS within a single incubation. With this methodological advance, Grow-C will reveal microbial C allocation strategies under short-term heat and drought stress in laboratory incubations and decipher long-term adaptive responses in field experiments (with >18 years of recurrent drought and >60 years of sustained warming). I hypothesize that stress shifts C allocation from replicative growth to survival strategies, with short-term stress favoring ISC and long-term adaptation promoting EPS production. By integrating non-replicative growth processes into C allocation, Grow-C will deliver a transformative framework and toolkit for better representing soil microbial processes in carbon–climate feedbacks. It will also enable more accurate predictions of future SOC stocks, addressing an urgent need in the face of climate change.