| The concept of plant composition has played an important role in the development of ecosystem ecology, as both plant species and plant functional groups control important ecosystem processes, such as nutrient cycling and carbon storage. More recently, ecosystem ecologists are becoming aware that identifying and classifying the functional roles of groups of soil microorganisms has tremendous potential in predicting the impacts of global change on ecosystem processes. Unlike plants, the major challenge in developing a functional classification system for microorganisms is our present inability to identify the vast numbers of soil microorganisms and their potential functions. Despite the major gap in microbial identification, many important patterns and relationships can be discovered with existing methods and knowledge. In my dissertation research, I use microbiological and biogeochemical techniques to: (1) Examine the impacts of global change (plant invasions, elevated CO2, and N addition) on plant and soil microbial community composition and structure; and (2) Determine how changes in plant and microbial composition or structure influence ecosystem processes. I found that the impact of different global change factors on soil microbial community composition and function is highly dependent on plant composition, soil conditions, and site history. The interaction of global change factors, such as elevated CO2 and N addition, can also influence soil microbial community composition in different ways, which complicates predictions of how global change impacts soil processes. Functional groupings of plants and soil microorganisms showed distinct patterns in responses to global change. For example, methane emissions showed distinct patterns among plant functional types, while a specific group of acetoclastic methanogens was influenced by both plant species and CO 2. Developing an ecologically meaningful classification system for both plants and microorganisms could improve current ecosystem models that aim to predict how global change and disturbances will impact ecosystem processes. |
