Abstract:
Soil organic carbon (SOC) plays a critical role in the global carbon cycle, yet its response to climate change remains uncertain. SOC exists in two distinct fractions—particulate organic carbon (POC) and mineral-associated organic carbon (MAOC)—which differ in their formation, stabilization, and loss mechanisms. While the current global distribution of POC and MAOC has been characterized, their vulnerability under future climate scenarios is poorly understood. Here, using 3,286 topsoil (0-30 cm) observations across six continents, we identify land cover and mean annual temperature as the primary determinants of POC and MAOC stocks. Under a high-emission scenario (SSP585), we project substantial POC losses in tundra and boreal forest soils by 2100, accounting for 89 ± 3% and 91 ± 5% of the predicted SOC losses in these land covers, respectively. These declines are attributed to the high proportion of SOC stored as POC (fPOC) and amplified warming at high latitudes. We show that fPOC is a robust indicator of SOC vulnerability to climate change. Globally, the projected decline in POC could result in a cumulative CO2 release of 224 Pg CO2e by 2100—equivalent to five times current annual anthropogenic CO2 emissions. These findings highlight the critical importance of preserving POC to mitigate climate feedbacks and safeguard soil carbon stores.

Bio:
Dr. Ji Chen received his Ph.D. from Chinese Academy of Sciences in 2016. After a short period of postdoc in the University of Exeter, he works as a tenure track in Aarhus University from 2018. His research aims to identify the mechanisms driving ecosystem carbon, nitrogen, and phosphorus dynamics in responses to global change drivers and anthropogenic disturbances. During my Ph.D., I explored the responses and underlying mechanisms of ecosystem CO2 exchange to experimental warming, herbivory grazing, and prescribed fire. During my postdoc, I investigated the microbial and extracellular enzymes mediated soil carbon, nitrogen, and phosphorus dynamics to nitrogen addition, drought and altered precipitation. During my current work, my work deals with the effects of farmland managements on ecosystem carbon, nitrogen, and phosphorus dynamics, as well as the extracellular enzyme mechanisms. Multiple research methods are widely used in my research, including field manipulative experiments, lab incubation, meta-analysis, data-assimilation and data-driven modelling. The overarching purpose is to make our world more resilient, resource-efficient and sustainable.