Soil fauna may buffer the negative effects of drought on alien plant invasion

Abstract

Assessing how climate change affects the potential invasion risk of alien plants has garnered considerable interest in ecology. Although many studies have tested the direct effects of drought on alien plant invasion, less is known about how drought affects alien plant invasion indirectly via other groups of organisms such as soil fauna. To test for such indirect effects, we grew single plant of nine naturalized alien target species in pot mesocosms with a native community of five native grassland species under four combinations of two drought (well-watered vs drought) and two soil-fauna (with vs without) treatments. We found that drought decreased the absolute and the relative biomass production of the alien target plants, and thus reduced their invasion success in the native community. Inoculation with a soil fauna increased the biomass of the native plant community and thereby decreased the relative biomass production of the alien species. The increased invasion resistance due to soil fauna tended (p = 0.09) to be stronger for plants growing under well-watered conditions than under drought. Our multispecies experiment shows for the first time that soil fauna might help native resident communities to resist alien plant invasions, but that this effect might be diminished by drought.