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University of Florida (2018)

THE EFFECTS OF PLANT INVASION AND DROUGHT ON PLANT-SOIL INTERACTIONS

Fahey Catherine

Titre : THE EFFECTS OF PLANT INVASION AND DROUGHT ON PLANT-SOIL INTERACTIONS

Auteur : Fahey Catherine

Université de soutenance : University of Florida

Grade : Doctor of Philosophy (PhD) 2018

Résumé
Plant-soil interactions are major drivers of plant community dynamics and are likely to be altered by anthropogenic global change with consequences for ecosystem structure and function. Interactions among global change factors have the potential to exacerbate ecological effects, but these interactions are notoriously difficult to predict. Plant invasions are accelerating worldwide with consequences for biodiversity, nutrient cycling, and disturbance regimes. Furthermore, plant invaders will experience shifts in abiotic conditions associated with climate change such as increased frequency and severity of drought. Here, I present research on the responses of plant and soil communities to interacting stressors and assess the potential consequences for ecosystem restoration. First, I assessed the response of longleaf pine forest plant communities to experimental invasion by Imperata cylindrica and experimental drought imposed with rainout shelters over four years. I found that invasion caused severe declines in diversity and shifts in composition of the native plant community, while drought had moderate effects on diversity and shifted the dominant functional groups. Soil moisture under drought conditions with the invader was higher than without the invader, and in combination the impacts of invasion and drought were lower than expected, indicating an ameliorating effect. Additionally, I evaluated the effects of invasion and drought and the consequent shifts in plant community on the soil microbial communities. On the whole, drought was a stronger driver of bacterial communities than invasion, whereas fungal communities were interactively affected by the treatments. Functional groups of importance for plant communities including plant pathogens, mycorrhizal fungi, and nitrifiers were affected by both invasion and drought. Finally, I assessed the impacts of these shifts in soil microbial communities in response to invasion and drought on growth and competition of the dominant plant species in this ecosystem (longleaf pine and wiregrass). Interestingly, the effect of soil microbes on plant growth varied with competitive context. Additionally, soil legacy of invasion decreased the growth of wiregrass but not pine. Collectively, my research provides an evaluation of the role of plant invasion and drought on interactions in the plant-soil system and addresses the implications for native ecosystems under future biotic and abiotic conditions

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