IBL Tropical Forest Research Program Microbiology One of the long-term goals of our research is to begin to understand the relationship between soil processes and the identity of the organisms carrying out those processes. Current measurements of biogeochemical variables (e.g., soil CO2 efflux) most often represent the net effect of the processes carried out by a suite of microorganisms. However relationships between the structure of the soil microbial community and specific biogeochemical processes are not well understood, especially in tropical ecosystems. Thus, one primary objective of our work is to study linkages between microbial community composition and specific biogeochemical processes. In collaboration with Dr. Diana Nemergut at INSTAAR, we are using molecular microbiological techniques to attempt to link the composition of the microbial community (i.e., phylogeny) to a specific functions (e.g., dissolved organic carbon (DOC) decomposition). Previous data from our site in Costa Rica suggest that both short term (diurnal) and long term (seasonal – annual) changes in soil resource availability drive changes in microbial community structure and function. Such information is critical for assessing the role of soil diversity in regulating ecosystem function. To promote interdisciplinary research linking biogeochemistry and microbiology, Dr. Nemergut has established a new microbiology and DNA lab at INSTAAR, and in collaboration with her, our group is helping to develop the Center of Microbial Biogeochemistry and Evolution (COMBE). Both this new lab and the new program will provide valuable resources for current and future students interested in developing research that combines biogeochemistry and microbiology. Another objective of our research is to begin to investigate how differences in tree diversity (reflected as differences in plant leaf chemistry) regulate soil microbial community structure and function. Our previous data suggest substantial between-species differences in the C and nutrient stoichiometry of litter leachate, and that variations in the nutrient content of leach dissolved organic matter (DOM) drive differences in the proportion of that DOM that is lost as CO2. We believe such differences occur via changes in microbial community composition resulting from differences in litter chemistry. To begin to address the links between above- and belowground species composition, we have established a set of litter manipulation plots in which we control litter composition. We are using several species that vary in C, N and P content, and are assessing the effect of tree diversity on DOM production and chemistry, belowground respiration and rates of nutrient cycling, and belowground community composition. This experiment is a useful first step in determining the connections between plant and soil diversity, and will provide insight into how belowground diversity regulates belowground ecosystem function.