Invasive species are known to alter ecosystem processes, often by altering their microbial controllers. If these effects persist beyond removal of the invader and impede ecosystem recovery, they may impact long-term landscape trajectories. We have examined persistent effects of two non-native grasses, bahia grass (Paspalum notatum) and natal grass (Rhynchelytrum repens), in a central Florida scrub ecosystem. We removed grasses using herbicide and followed potential biogeochemical and microbial legacies important for reestablishment of the plant community. Specifically, over two years we measured the persistent effects of former vegetation on standing pools and gross transformation rates of soil nitrogen, as well as the abundance and composition of algae, bacteria, and fungi in soil microbial communities.

Results/Conclusions

Sites dominated by invasive grasses were significantly different from native scrub sites in all seasons, with more available nitrogen, fewer active algae, and more extensive fungal networks. Grass removal initially led to a pulse in available nitrogen and temporary reductions in active algae and soil fungi. The legacy of former vegetation could still be observed even 14 months post-removal, however, with nitrogen pools 103% greater, rates of microbial nitrogen fixation up to 60 times lower, and rates of mineralization and nitrification up to 300% greater compared to native scrub. In addition, plant community resilience was lower in formerly invaded sites, with germination and establishment of native seedlings reduced by a factor of 2-15. Resilience of the plant community from the impacts of invasive species is likely to be inextricably tied to recovery of biogeochemical and microbial properties of the ecosystem.