| Traditionally, ecosystem scientists have focused on the role of abiotic factors such as temperature or water in controlling process rates while microbiologists have focused on the population ecology of microorganisms. More and more, however, we are seeing microbial ecology studies showing that microorganisms can be explicit determinants of soil function and nutrient availability. The impact of future global changes may best be addressed by research that integrates population and community ecology with process study.; My work was designed to further this integration. I addressed two questions: (1) How should we measure microbial community composition and function, in order to link microbiology and nutrient cycling at the ecosystem scale? (2) What is the relative importance of microbial community characteristics versus abiotic factors (such as temperature or soil water) in controlling nutrient cycles and ecosystem response to climate change or disturbance?; To make a quantitative link between measures of community characteristics (biomass, activity, diversity) and ecosystem processes, I combined a field manipulation of climate (reciprocal soil transplant between grassland and conifer ecosystems in the Sierra Nevada of California) with a suite of laboratory analyses to tease apart the relationships among changes in environment, microbial community characteristics, and soil processes. I worked extensively with two techniques for studying soil communities: phospholipid fatty acid analysis (PLFA), and substrate utilization patterns (BiOLOG assay). From this I gained an understanding of the temporal patterns of community change after disturbance and how this constrains process rates.; In addition to developing a quantitative framework for linking microbial community characteristics with nutrient cycles, I was interested in whether microbial communities from different ecosystems respond the same way to a given change in environment. I found that the grassland and conifer microbial communities I studied did not respond the same way to a change in climate. Further study indicated that these and other microbial communities (from Puerto Rico and Alaska) are adapted to their native climatic regime. This suggests that a soil community in an area of wide climatic fluctuation may respond to global changes and disturbance very differently than a community from a stable environment. |
