Loss of faster-cycling soil carbon pools following grass invasion across multiple forest sites

It is established that invasive plant species can alter soil carbon cycling, although data are rare for late successional ecosystems. We examined effects of a grass invader (Microstegium vimineum) on soil carbon across eight sites in southeastern U.S. forests to establish which factors are related to these effects, by coupling isotopic and soil carbon fractionation approaches. Invasion was associated with declines in mass of faster-cycling, particulate organic matter (POM) carbon pools. This led to a significant decline (11% on average) in native-derived carbon in the surface 10 cm of the soil profile. Formation of soil carbon from the invader-derived inputs partially mitigated these losses (total carbon loss 6% on average). Our data suggest that Microstegium invasion of forest understories may accelerate carbon cycling and could result in a net loss of soil carbon from eastern U.S. forests.