Exotic plants have the ability to modify soil seed banks and the soil biotic community in habitats they invade, but little is known about the legacy of invasion once an exotic plant has successfully been controlled. Natural areas previously invaded by leafy spurge in the northern Great Plains typically have one of two fates following control of spurge: a return of native plants, or a secondary invasion of other exotic plants. Furthermore, reduced native plant recruitment has been observed in areas where insect biocontrol has been used for leafy spurge control. It is unknown, however, if the reduced recovery of natives is due to a depauperate native plant seed bank, altered soil biotic communities, or interactions of leafy spurge with biocontrol organisms. To address the seed bank question, I monitored soil seed banks and standing vegetation for two years in mixed-grass prairies that were previously invaded by leafy spurge. I found that native plant seed banks were largely intact in areas previously invaded by leafy spurge, regardless of the current living plant community. I conducted a glasshouse experiment to investigate interactive effects of leafy spurge soil conditioning and flea beetle biocontrol insects on native plants. My results indicate that leafy spurge soil conditioning inhibits native plant germination and growth, and that flea beetles have similar inhibitory effects but only on particular native plant species. Lastly, I investigated the interactive effects of leafy spurge root exudates and fungal pathogens on native plant growth in a glasshouse, and the degree to which fungal pathogen growth varies with leafy spurge and native plant root exudates in petri dishes. I found that leafy spurge root exudates and fungal pathogens, when applied together, tended to enhance native plant germination and growth, and that fungal pathogen growth response to root exudates varied between fungal genera, and among native species, but that fungal growth did not respond strongly to leafy spurge exudates. Therefore, regardless of the relatively unaltered native plant seed banks, leafy spurge soil occupancy and fungal pathogens may have significant impacts on native plant recovery.
University of Minnesota Ph.D. dissertation. Major: Ecology, Evolution and Behavior. Advisors: Diane L. Larson and Linda L. Kinkel. 1 computer file (PDF); xiii, 240 pages, appendices 1-14.
Haines, Dustin F..
Invasive plants, herbivores and the underground: feedbacks with soil biota and their influence on grassland plant communities in the Great Plains.
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