3e série de séminaires CLIMACT - Episode #6

Soils contain the largest dynamic stock of carbon (C) on the planet, with soil organic matter (SOM) containing approximately twice the amount of C stored in the surface oceans and three-times that in the atmosphere. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate and land use change. Recent analytical and experimental advances have undermined the long-standing theory that molecular structure alone controls SOM turnover; instead, SOM turnover is now considered an ecosystem property, rendering associated C stocks much more vulnerable to environmental change. In this talk, I will highlight how plants, microbes, and minerals interact to regulate SOM turnover within soil ecosystems. I will further show that explicit consideration of such ecosystem controls, together with climatic variables, is critical for improved predictions of soil carbon-climate feedbacks as well as management strategies aimed at sustaining soil health.

Electron transfer (redox) reactions are central to the transformation of energy in the environment and play an important role in the cycling of elements. In soils, one of the main drivers of carbon cycling is the activity of organisms that utilize the energy stored in soil organic matter by extracting electrons from organic carbon and transferring them to various electron acceptors. Yet, our understanding of this process is incomplete and the response of the soil carbon pool to climate change remains one of the primary sources of uncertainty in projections of atmospheric carbon dioxide concentrations. Here, I highlight the relevance of redox reactions in soils and, specifically, the role of redox-active minerals in soil carbon cycling under oxygen-limited conditions.