Seminar: Hui Wang

Reliable predictions of dryland carbon fluxes require understanding the persistence and turnover of soil organic carbon (SOC). We measured radiocarbon in bulk SOC and respired CO2 from 97 dryland sites across six continents. Bulk SOC radiocarbon indicated that little stored C was fixed in the past 60 years, while respired CO₂ originated from both bomb-derived recent C and millennia-old C—challenging the idea that old C is chemically or physically protected. Radiocarbon of respired CO2 suggested a mean turnover time of c. 500 years, far longer than estimates from machine learning (<50 years) or Earth system models. Aridity, net primary productivity, and SOC content were dominant predictors for the age of bulk and respired C, with abrupt shifts occurring across an aridity threshold of ~0.87. Our findings underscore the need to incorporate the vulnerability of older carbon into ESMs and land management strategies.