Limits, controls, and vulnerability of mineral-associated soil organic carbon

Managing soils to increase organic carbon storage presents a potential opportunity to mitigate and adapt to global change challenges, while providing numerous co-benefits and ecosystem services. However, soils differ widely in their potential for carbon gains and losses, and advancing knowledge of biophysical limits to carbon accumulation may aid in informing priority regions for management. There is thus increasing interest in assessing whether soils exhibit a maximum capacity for storing organic carbon (i.e., carbon saturation), especially as mineral-associated organic carbon given its presumed greater persistence and the finite nature of reactive minerals in soils. In this award lecture, I will summarize my ongoing work on the controls and limits of mineral-associated organic carbon and its representation in process-based soil carbon models. First, I will provide an overview of the concept of soil carbon saturation at both micro- and macro-scales, address common misconceptions, and present a quantification of the maximum observed capacity of mineral-associated organic carbon globally. Next, I will show that organo-mineral associations can moderate the vulnerability of a soil to lose carbon under climate or land-use change. Finally, I will review the landscape of current ecosystem- to global-scale soil carbon models and highlight next steps for improving their structure and parameterizations in this context.