Plant species coexistence
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Plant soil feedbacks, specifically soil microbial communities, have been proposed to affect plant species’ relative abundances and stabilize coexistence within a community. Negative plant soil feedbacks, where plant species condition microbial communities detrimental to conspecifics, may promote coexistence and plant diversity within a community both by lowering overall fitness and creating negative frequency dependence, i.e. stabilizing niche differences. Positive plant soil feedbacks, where plant species condition communities beneficial to conspecifics, may promote the dominance of a species through increased overall fitness and reduced negative frequency dependence. Invasive species can disrupt coexistence and reduce resident species abundance and diversity in its invaded range, potentially due to a more neutral to positive interaction with the soil microbial community resulting from an escape from specialized pests and pathogens in its native range. However, a more antagonistic soil community could accumulate through time to reduce the dominance of the invader and promote coexistence between it and native plant species. We explored whether the propensity to coexist increased due to the presence of soil biota, as well as whether the likelihood of coexistence increased across invasion history for invasive Microstegium vimineum and native plants due to changes in the soil community. In an observational study across M. vimineum’s invasive range in the eastern United States, we found a decline in M. vimineum’s survival at low frequency and changes in its soil/root fungal community across invasion history. In a 2-year field experiment negative frequency dependence increased for M. vimineum across invasion history in conspecific conditioned soil. Finally, in a greenhouse experiment we found that the soil community promoted coexistence of M. vimineum and native Pilea pumila through increased stabilizing niche differences. These results combined show that the soil community promotes coexistence through stabilizing interactions and that the likelihood of coexistence between invasive M. vimineum and native plants is potentially increasing through invasion time due to an accumulation of an antagonistic soil community.