Intraspecific diversity mitigates the negative soil-legacy impacts of an invasive plant.

Elton's biotic resistance hypothesis predicts that biodiversity can resist the establishment of invasive plants. However, whether and how within-species diversity mediates the impacts of successfully established invaders is poorly understood, particularly in the face of climate change. We used an experimental system to test the effect of intraspecific diversity of a native foundation species, Scirpus mariqueter, on the soil-legacy impacts of a global plant invader, Spartina alterniflora, under well-watered and drought conditions. We found that more diverse populations of the native plant buffered against the negative soil-legacy impacts of the invader on the native plant. This intraspecific diversity effect was due to a complementarity effect triggered by invader-shaped soil biota, and emerged in both well-watered and drought conditions. Compared with the previous finding that intraspecific diversity of the native plant can reduce the performance of the invader through soil biotic feedbacks, this study provides further evidence that it helps to mitigate the negative soil-derived impacts of the invader. These findings together emphasize the need for management measures that promote and restore native intraspecific diversity in a changing world.