Soil organic carbon response to climate warming depends on its distribution between particulate and mineral-associated organic matter pools

Abstract:

It is not yet clear how soil carbon (C) dynamics will feed back to climate warming. Part of this uncertainty may be due to studying the soil C pool as a whole, rather than separating it into its diverse components. To gain a greater mechanistic understanding of soil C dynamics, we performed a systematic meta-analysis on the response of soil organic carbon (SOC), mineral-associated organic carbon (MAOC), and particulate organic matter carbon (POC) to warming, and other global change factors. We found that warming reduced POC by 10.05%, suggesting reduced plant structural inputs and/or increased microbial activity, but had no effects on MAOC, which is less vulnerable to disturbance. Given the higher relative abundance of MAOC, we observed no overall effects of warming on SOC. Moderating effects on POC responses to warming suggested that it is crucial to contextualize SOC responses with microbial and plant responses. The response of POC to warming was moderated by degree of warming but the relationship changed from negative to positive when soil and air were warmed, respectively. This indicates that when soil is warmed, rather than air, there is a weaker plant response that modifies the soil response, cautioning against the assumption that soil and air warming experiments provide comparable data. In addition, POC decreased more under warming at higher latitudes, suggesting microbial decomposition is more strongly temperature limited than plant input in those regions. Moderating influences of climate and soil variables on other global changes evaluated in our study further imply that MAOC and POC can provide indication of whether plant and microbial inputs or destabilization and microbial decomposition processes are driving the total SOC response to global change. By incorporating SOC fractions into models and management plans, we will be able to better understand the feedbacks of SOC to warming and gauge whether promoting SOC storage can help mitigate the climate crisis.