| Abstract |
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.
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