Abstract

Forested ecosystems around the world are becoming increasingly vulnerable to non-indigenous plant invasions. Garlic mustard (Alliaria petiolata), a naturalized non-native plant species, has successfully invaded woodland habitats across much of the eastern United States because of its highly competitive abilities and the production of allelopathic compounds. The species can limit the growth of native understory species and tree seedling establishment thereby altering community composition and biodiversity by disrupting relationships with various mycorrhizal symbionts. However, the potential adverse effects of garlic mustard allelopathy on saprotrophic fungi have not yet been assessed. We experimentally tested the effects of garlic mustard on growth and fruiting of a widespread saprotrophic fungus, oyster mushroom (Pleurotus ostreatus). First year garlic mustard was planted in plastic bins with oyster mushrooms over a 16-week period and were monitored for fruiting body production. We also examined the potential allelopathic effects of garlic mustard on decomposition rates in heavily invaded and uninvaded areas in the Pisgah National Forest of western North Carolina. Forty pairs of litterbags were placed in the field in April 2015. A random subset of these were retrieved after six months and one year in the field and decomposition rates were calculated from mass lost over time. Fruiting body mass totals had no difference between the invaded microcosms and our controls (p = 0.8637). Fruiting body mass was significantly (p < 0.001) affected by time, however, there was no difference between invaded and control plots (p = 0.8243). Under field conditions, we found no significant difference in decomposition between garlic mustard in invaded and uninvaded plots in our six-month treatment (p = 0.21) and one-year treatment (p = 0.87). However, there was a nearly significant (p = 0.0596) decrease in decomposition with increasing garlic mustard stem density. Decomposition rates may have also been confounded by the abundance of an allelopathic tree species (p = 0.0726), black walnut (Juglans nigra) at the site.

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