Invasive Plant Management Techniques Alter Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhizal (AM) fungi can improve restoration outcomes by facilitating establishment of native plants. Yet, we know little about the effects of restoration methods on AM fungi. We examined how using herbicide and mowing to remove invasive Brassica nigra (black mustard) might alter AM abundance in a coastal sage scrubland. Black mustard is a non-mycorrhizal plant that produces allelochemicals that inhibit AM fungi. Although black mustard removal could potentially improve AM growth, herbicide and mowing might harm AM fungi. We measured black mustard cover, AM hyphal abundance, and native plant cover from plots exposed to either herbicide or mowing versus untreated controls. We found that both herbicide and mowing reduced black mustard cover. Furthermore, herbicide increased AM abundance in one field site, potentially because herbicide killed black mustard roots and reduced allelochemical production. However, neither restoration treatment improved native plant abundance over the course of our study. Overall, herbicide can deter black mustard invasion and help re-establish the AM community in certain ecosystems, but without a corresponding increase in native plants.