Elevated CO 2 and plant species diversity interact to slow root decomposition

Abstract

Changes in plant species diversity can result in synergistic increases in decomposition rates, while elevated atmospheric CO 2 can slow the decomposition rates; yet it remains unclear how diversity and changes in atmospheric CO 2 may interact to alter root decomposition. To investigate how elevated CO 2 interacts with changes in root-litter diversity to alter decomposition rates, we conducted a 120-day laboratory incubation. Roots from three species ( Trifolium repens, Lespedeza cuneata, and Festuca pratense) grown under ambient or elevated CO 2 were incubated individually or in combination in soils that were exposed to ambient or elevated CO 2 for five years. Our experiment resulted in two main findings: (1) Roots from T. repens and L. cuneata, both nitrogen (N) fixers, grown under elevated CO 2 treatments had significantly slower decomposition rates than similar roots grown under ambient CO 2 treatments; but the decomposition rate of F. pratense roots (a non-N-fixing species) was similar regardless of CO 2 treatment. (2) Roots of the three species grown under ambient CO 2 and decomposed in combination with each other had faster decomposition rates than when they were decomposed as single species. However, roots of the three species grown under elevated CO 2 had similar decomposition rates when they were incubated alone or in combination with other species. These data suggest that if elevated CO 2 reduces the root decomposition rate of even a few species in the community, it may slow root decomposition of the entire plant community.