Date of Award

Spring 2024

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

Serita D Frey

Second Advisor

Jessica Ernakovich

Third Advisor

Stuart Grandy

Abstract

Invasion of temperate forests by Alliaria petiolata (garlic mustard) may be affected by interactions with arbuscular mycorrhizal fungi (AMF). Although AMF are generally mutualists of land plants, they suppress the growth of close relatives of garlic mustard1–3. Garlic mustard produces indolic glucosinolates, a class of organic compounds known to suppress AMF4,5 and which may protect the plant from AMF antagonism. We would therefore expect a negative interaction between these organisms. Contrary to this expectation, we show that AMF inoculation promotes garlic mustard growth, and this effect is influenced by investments in plant defense. AMF inoculation and subsequent colonization increased plant growth in three geographically distinct garlic mustard populations, both in controlled laboratory conditions and in an in situ natural invasion. In contrast to typical arbuscular mycorrhizal symbioses, AMF did not produce arbuscules within garlic mustard roots where nutrient exchange occurs, but AMF inoculation did increase tissue N content and soil inorganic nitrogen availability. AMF inoculation also shifted glucosinolate production, with a strong negative correlation between glucosinolate production and plant growth. Our findings reveal a new phenotype of AMF symbiosis which lacks arbuscules but still promotes plant growth in the presence of an adjacent mycorrhizal symbiont. Prior assumptions that garlic mustard suppresses AMF are inadequate to explain the success of this invader since it clearly benefits from interactions with AMF. This study is the first to demonstrate simultaneous increases in plant biomass and tissue N with AMF inoculation in a mustard plant, with important implications for invasion biology and agriculture.

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