Arbuscular Mycorrhizal Fungi Boost Development of an Invasive <i>Brassicaceae</i>

Invasive plant growth is affected by interactions with arbuscular mycorrhizal fungi (AMF). AMF are mutualists of most land plants but suppress the growth of many plants within the Brassicaceae, a large plant family including many invasive species. Alliaria petiolata (garlic mustard) is a nonnative, nonmycorrhizal Brassicaceae distributed throughout North America in forest understories where native species rely on AMF. If AMF suppress growth of garlic mustard, it may be possible to inoculate AMF to manage invasions. Here, we show that in contrast to expectation, garlic mustard growth nearly doubled in response to AMF inoculation under both laboratory and field conditions. This effect was negatively linked to investments in glucosinolates, a class of defensive compounds. In contrast to typical symbiosis, AMF did not produce arbuscules where nutrient exchange occurs in roots, but AMF inoculation increased plant and soil nitrogen availability. Our findings reveal an adjacent pathway by which AMF promote invasive plant growth without classic symbiotic exchanges. Prior assumptions that garlic mustard suppresses AMF are inadequate to explain invasion success since it benefits from interactions with AMF. This study is the first to demonstrate extensive growth promotion following AMF inoculation in mustard plants, with important implications for invasion biology and agriculture.