Date of Award
Master of Science
Ecology and Evolutionary Biology
Jennifer A. Schweitzer
Daniel Simberloff, Joseph K. Bailey, Charles Kwit
Anthropogenic global change is occurring today at a faster rate and larger scale than ever before. Understanding how plants will respond to such large-scale disturbance is critical for biodiversity conservation, yet the ecological and evolutionary mechanisms underlying these responses remain poorly understood. In this thesis, I investigated the mechanisms underlying plant response to two major drivers of global change, climate change and the widespread mortality of foundation species. First, I examined genetic and plastic plant trait responses to climatic variation using elevation gradients, which serve as space-for-time substitutions for climate change. Through field observations in three populations of the North American shrub Rhododendron maximum (rosebay rhododendron), I found that while several traits respond significantly to elevation, these trait responses typically occur in some, but not all, populations. A common garden experiment indicated that trait variation within and among populations was driven by plasticity and genetic divergence, respectively. These findings suggest that plasticity can be a viable climate change response, although the magnitude of this plasticity will likely differ among genetically distinct populations. Next, I examined whether plant-soil biota interactions and/or light variation associated with foundation tree decline mediate the expansion of R. maximum in southeastern US forests where Tsuga canadensis (eastern hemlock), a dominant foundation tree species, is declining due to non-native insect invasion. Using a controlled inoculation experiment, I found that, in high light (matching infested T. canadensis crowns), R. maximum seedling performance was highest in T. canadensis-conditioned soils, medial in R. maximum-conditioned soils, and lowest in interspace soils. Genomic sequencing indicated that such variation in performance can be attributed to variation in mycorrhizal and saprotrophic soil fungal guilds. In low light (matching healthy T. canadensis crowns), however, soil inoculation did not affect plant performance and plants performed worse on average. These findings suggest interactions with soil biota can act synergistically with altered light environments to mediate species’ responses to widespread foundation tree mortality, providing evidence for a novel mechanism of plant response to major disturbance. Overall, my work suggests that plant persistence in a changing world will depend on multiple mechanisms, including plasticity, genetic differentiation, and biotic interactions.
Pfennigwerth, Alix Ann, "Plasticity and biotic interactions mediate plant persistence in a changing world. " Master's Thesis, University of Tennessee, 2017.