Elevated CO₂ and Plant Species Diversity Interact to Slow Root Decomposition

<p> <p id="x-x-x-x-x-x-abspara0010"> 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 ( <em> Trifolium repens </em> , <em> Lespedeza cuneata </em> , and <em> Festuca pratense </em> ) 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 <em> T. repens </em> and <em> L. cuneata </em> , 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 <em> F. pratense </em> 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. </p></p>