Can an invasive African grass affect carbon and nitrogen stocks in open habitats of the Brazilian Cerrado?
Considering the emergence of ecosystems dominated by invasive species, there is growing interest in estimating the effect of biological invasions on ecosystem processes and provision of services. African grasses are the most invasive plants in the Cerrado (Brazilian savanna), but their impact on C and N stocks is poorly known. We compared patterns of C and N stocks in the aboveground biomass, root biomass and soil in open Cerrado (campo sujo) sites, both uninvaded and invaded by the African grass Urochloa decumbens. In both sites we estimated the aboveground biomass of U. decumbens and native grasses, as well as the root biomass up to 50 cm. We obtained C and N soil content and soil bulk density up to 1 m depth, which were used to obtain the overall soil C and N stocks; we also assessed the variation in soil δ13C and δ15N. Although invasion did not affect the aboveground biomass, it did affect belowground biomass, leading to more C stocked in fine roots and soil, higher N concentration close to soil surface, and also more C along the soil profile. C and N soil stocks, soil δ13C and δ15N values did not significantly differ between invaded and uninvaded site. Even a relatively low level of invasion by U. decumbens changed the root distribution pattern and increased C and N contents in the upper soil, which may promote ecosystem changes by altering nutrient dynamics. Although our study was conducted at a single site, it clearly shows effects of the invasive species on the belowground environment, and indicates the necessity of further studies.