VOLATILE ORGANIC CARBON METABOLITES AS INDICATORS OF SOIL MICROBIAL COMMUNITY SHIFT IN MICROCOSM STUDIES

The use of environmental indicators in aquatic and soil ecosystems are important for both the prediction of future system behavior and the impact of natural and anthropogenic disturbances on the system. Frequently, soil and aquatic scientists utilize organic, inorganic and genetic biomarkers in the solid (e.g. lipids), liquid (e.g. porewater ions) or gaseous phases (e.g. CO2); their selection may depend upon the type of information that is required in regard to the carbon sources and/or microbial communities and the ease of sample analysis. For example, porewater and CO2 measurements although easiest to measure are limited in information quality, whereas lipids are very informative but are tied to rigorous extraction procedures. It is the aim of this research to pursue a methodology to utilize VOCs (volatile organic carbons) as useful, informative, and relatively easy to measure indicators of microbial community shift during perturbations of various environmental factors. The development of a laboratory microcosm method to measure VOC metabolites using gas chromatography and mass spectrometry (GC-MS) is presented in this research where the measurements of carbon dioxide via infra-red technology, microbial community with Biolog and fatty acid methyl ester (FAME) techniques, and microbial biomass using the Bradford protein assay are also conducted. Experiments with surface soils collected from the coastal margin region in southern Texas are performed where environmental factors such as soil water content and soil type are manipulated. Results indicate that over fifty identifiable VOC metabolites are produced from the soils, where several compounds are evidenced as direct indicators of shifts in microbial community and activity through principle component and regression analyses (p < 0.05). These findings are useful for soil and aquatic scientists alike, as shifts in dominant microbial communities are a common occurrence in both ecosystems. However, a distinctly proven, easy to measure, and relatively inexpensive method that requires small samples sizes and provides quality information about both the carbon sources and the microbial communities present in the system, such as the VOC microcosm analysis presented here, is not often available. Implications for in-situ and aquatic uses are discussed.