Despite a growing body of work that quantifies factors that drive biodiversity loss, accurate assessment and prediction of the impact of invasive species on native ecosystems remains controversial and challenging. Connecting small-scale mechanistic knowledge to regional invasion impact is crucial to addressing this shortcoming. One such invasion mechanism is the mutualism disruption hypothesis. For example, a non-mycorrhizal plant invader can gain a fitness advantage over native mycorrhizal plants because they destroy the beneficial native plant-fungal association. One such invader is garlic mustard (Alliaria petiolata), which produces chemical compounds that are toxic to mycorrhizal fungi. Disruption of mycorrhizal associations by garlic mustard is known to cause physiological stress in native plants, resulting in diminished plant growth and reproduction. There is strong support for this mechanistic process in individual native plant response, but it is unknown if mutualism disruption scales up to impact plant community metrics. To test the effects of mutualism disruption on plant communities, we combine an experimental manipulation of garlic mustard presence with regional plant abundance surveys. In both the manipulative experiment and the plant surveys, we expect garlic mustard presence to have a stronger negative effect on mycorrhizal herbaceous plant cover in comparison with non-mycorrhizal plant species.
Results/Conclusions
Over a 10 year period, experimental removal of garlic mustard resulted in a significant increase in mycorrhizal herbaceous cover, but not a similar increase in percent cover of non-mycorrhizal herbs. This suggests that the presence of garlic mustard selectively inhibits mycorrhizal plant species, consistent with the mutualism disruption hypothesis. Additional work will include assessing the impact of garlic mustard on mycorrhizal and non-mycorrhizal plant cover at a range of garlic mustard abundance across this invaders’ range in North America. Invasive species with novel weapons pose a threat to naïve native species and interactions. Garlic mustard’s chemistry harms mycorrhizal fungi in the soil, causing physiological stress in native plants that compounds over time and results in decreased biomass of plants that rely on mycorrhizal fungi.