Dissertation Research: The Effect of Plant Community Composition and Land-use Change on Soil Microbial Community Composition and Function

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PROJECT SUMMARYLand-use change and alterations of plant diversity and composition have been shown toinfluence ecosystem processes. Until recently, however, there has been little evaluation ofthe role of microbial community changes in mediating process change. Shifts in land-useand plant diversity may alter the composition, and thus collective physiology, of soilmicrobial communities, leading to differences in process rates. To understand more fullythe factors that influence microbial communities and their functioning, our researchaddresses the following questions: 1) Does plant diversity and/or land-use influence soilmicrobial community composition? 2) Do these changes in microbial compositioninfluence nutrient cycling rates? We are addressing these questions using an experimentin Costa Rica that manipulates plant community composition and diversity as well as aset of land-use sites, including forest and pasture. To address the first question, we areexamining microbial community composition using phospholipid fatty acid analysis(PLFA) and terminal restriction fragment length polymorphisms (T-RFLP). PLFA datasuggest that microbial communities differ significantly across plant diversity and land-use gradients. We request funds to proceed to the crucial second question and test, usingcontrolled laboratory experiments, whether soils with distinct microbial communitiesdiffer in two critical ecosystem functions: nitrification and litter decomposition.