| Among ecologists there is an increasing awareness and interest in the role of soil microbes in the distribution of plants and functioning of ecosystems. This dissertation relates soil microbial community composition to plant growth, habitat type, and decomposition with particular emphasis on invasive plants.; I examined growth, physiology and competitive ability of an invasive shrub, Ardisia crenata, in two greenhouse experiments. When grown singly, relative growth rates (RGR) and leaf area ratio (LAR) were higher for seedlings inoculated with mycorrhizal fungi isolated from Ardisia roots than those inoculated with single-spore isolates and nonmycorrhizal controls. In a second experiment, Ardisia was grown with a conspecific or heterospecific (Prunus caroliniana) competitor. While neither identity of competitor nor mycorrhizal status had a great effect on Ardisia growth, Prunus growth was significantly depressed in competition with Ardisia in the absence of mycorrhizal fungi.; In chapter 2, I examined soil microbial communities from five different habitats prone to invasion by an invasive plant using phospholipid fatty acids (PLFA) and Biolog substrate utilization. Habitat type had the largest effect on microbial community composition. Moisture content of soils and, to a lesser extent, carbon and nitrogen contents appeared to be driving differences in biomarker PLFAs. Although the largest differences in soil microbial community composition were found among habitats, invasion altered microbial community composition within habitats.; In chapter 3, I placed litters of 20 native and non-native plant species of varying decomposability in a common site and quantified their decomposition. The composition of microbial communities on 11 of the litters was examined by PLFA at 28, 56 and 238 days. Microbial communities at the early (low moisture) sampling dates were more similar to one another than to the late (high moisture) sampling date. In addition to moisture effects, litter quality had a significant effect on microbial community composition. Both decomposition and microbial community composition were correlated with leaf chemistry. The best single predictor of decomposition rate was microbial community composition.; These results suggest that plant-microbial interactions are important in plant invasion, and explicit examination of a potential positive feedback on invasion through the microbial community should be further explored. |
