Legacy of pine invasion disrupts plant-soil feedback of native and non-native grasses.

Plant-soil feedback (PSF) is a standing concept helping to explain plant species coexistence. Accumulating evidence suggests that PSF depends on the environmental context. One particularly impactful disruption of the environmental context is the invasion of alien species into a community. While PSF between native and non-native species has been linked to invasion success, the effect of an invader on PSF between resident plants has received little attention. We explored how Pinus contorta (lodgepole pine) invasion impacts PSF between four resident grasses (two native and two non-native species). We grew the plants in live soil to condition species-specific soil communities, followed by a response phase where the plants were grown in conspecific and heterospecific soil. Both phases were performed with soil from uninvaded, invaded, or controlled invasion areas. Pairwise PSF between the species in uninvaded soil was negative and became neutral to positive in invaded soil. This effect persisted even after P. contorta removal. Our results suggest a destabilizing effect of P. contorta invasion on the coexistence of the resident grasses, benefitting non-natives over natives. This work exemplifies an overlooked mechanism by which an invader can alter interactions between resident species and adds a novel dimension to the context dependence of PSF.