2018 Winner: A Widespread Nitrogen-fixing Invader Experiences Negative Soil Feedbacks Despite Increased Root Nodulation and Mycorrhizal Colonization

Project Information
A Widespread Nitrogen-fixing Invader Experiences Negative Soil Feedbacks Despite Increased Root Nodulation and Mycorrhizal Colonization
Physical and Biological Sciences
BIOE195
Invasive species success can be inhibited or intensified by plant-soil feedbacks, in which plants modify the microbial community or abiotic environment of the soil in a way that in turn affects plant growth. Plant-soil feedbacks for introduced species can be either positive (favoring invasion) or negative (limiting invasion impacts). Cytisus scoparius (Scotch broom) is a globally invasive species that limits restoration and reforestation success through soil legacies. To better understand the success of C. scoparius, I investigated whether the invader exhibits positive or negative plant-soil feedback in its invaded range. I performed a greenhouse experiment using soils collected from a clearcut invaded by C. scoparius and nearby uninvaded forest. I compared C. scoparius above- and belowground biomass, root nodulation, and the abundance of roots colonized by arbuscular mycorrhizal fungi. Cytisus scoparius grown in invaded soils had 67% more root nodules than plants grown in uninvaded forest soil, suggesting that C. scoparius invasions into new areas may be limited by their nitrogen-fixing symbionts. Cytisus scoparius exhibited 72% greater AMF colonization in plants grown in invaded soils than in uninvaded forest soils, indicating a build up of fungal symbionts in invaded soils. Despite increased root nodulation and arbuscular mycorrhizal fungi, C. scoparius grew 21% smaller when grown in invaded soils than in uninvaded soils, indicating negative plant-soil feedback. Taken together, these results suggest that C. scoparius has not escaped soil enemies in its introduced range, but increased mutualistic interactions may contribute to C. scoparius’ persistence. Mutualistic soil biota may counteract negative effects of pathogen build up or nutrient depletion in C. scoparius invaded soils, leading to less negative plant-soil feedbacks which may help explain why C. scoparius persists in monospecific stands in invaded regions.
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Students
  • Elizabeth Jane Davis (Merrill)
Mentors