Getting to the root of soil carbon sequestration: tracking fine root carbon losses and soil carbon gains

First Author's Department

Biological Sciences

Third Author's Department

Biological Sciences



Document Type



Fine roots of woody plants are the greatest terrestrial source of carbon (C) to soils, hence represent a major flux of C out of the atmosphere. While the decomposition rates of many tree species’ roots have been measured in other experiments, such information doesn’t address how much root C is ultimately incorporated into microbial biomass, respired, leached to dissolved organic C pools, or stabilized as soil particulate organic matter (POM). We explored two different pathways by which plant litter becomes stabilized in soil: a physical pathway, where root fragments are protected from decomposition by microorganisms in soil aggregates, and a biochemical pathway, where labile plant tissues are utilized by microorganisms that, in turn, bond with minerals to form stable soil C. In two two-year long decomposition experiments with four tree species’ roots that had contrasting chemical and morphological properties, we monitored losses of root C and gains of C in various soil C pools. Preliminary results suggest that root morphology strongly affects which decomposition pathway predominates. Roots with smaller diameter and specific root length lose more C to fragmentation, becoming occluded in POM, while thicker roots contribute more C to microbial and dissolved organic pools, which have faster C turnover rates. Overall, more root C was stabilized in soil from roots with thin, highly-branched roots. Understanding which plant traits affect a tree’s potential as a C sink is important for improving our accounting of carbon in forests in a changing climate.