Fixing invasions: The effect of non-native, nitrogen-fixing species on plant community structure in Northeastern open-meadow habitats



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Nitrogen-fixing species that colonize new habitats often initially sustain high growth rates by exploiting nitrogen resources unavailable to other plants. Their continued presence can alter soil chemistry and create artificially high-nitrogen environments that facilitate the success of other invasive species. European clovers (Trifolium spp.) are non-native, nitrogen fixing forbs ubiquitous in Northeastern meadows. I performed field and greenhouse experiments to assess the effect of Trifolium spp. on naturally occurring plant communities and elucidate the mechanisms by which Trifolium increases soil nitrogen concentrations and impacts plant competition. The presence of the nitrogen-fixer facilitated non-native growth at the expense of native plant communities in both the field and pot experiments. Invasive Rumex acetosella plants grown in Trifolium-treated soil also demonstrated higher densities of vesicular arbuscular mycorrhizal nodules. The increased density of VAM nodules in the presence of Trifolium indicates a relationship between active nitrogen fixation and the recruitment of mychorrizal associations on R. acetosella. The extra nodules on the invader may provide a phosphorus source for the nitrogen fixer, which returns an elevated nutrient supply for the invader, forming a positive feedback loop that facilitates the growth success of both non-natives.



Invasion ecology, Nitrogen-fixation