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USE OF FATTY ACID STABLE CARBON ISOTOPE RATIO TO INDICATE MICROBIAL CARBON SOURCE IN TROPICAL SOILS
Citation:
Burke Jr., R A. AND M Molina. USE OF FATTY ACID STABLE CARBON ISOTOPE RATIO TO INDICATE MICROBIAL CARBON SOURCE IN TROPICAL SOILS. Presented at 3rd Annual International Conference on Application of Stable Isotope Techniques to Ecological Studies, Flagstaff, AZ, April 28-May 1, 2002.
Impact/Purpose:
The overall objective of this task is to develop quantitative relationships for assessing the vulnerability of aquatic resources to global change. The task will contribute experimental and modeling tools for assessments of the interactions of global climate and UV changes with coral reefs and selected watersheds and estuaries in the U.S. These activities are contributing primarily to two APGs in the ecosystems component of the Global Change Research Multiyear Plan: the 2006 APG (APG 3) on building the capacity to assess global change impacts on coastal aquatic ecosystems, including coral reefs and estuaries and the 2004 APG (APG 2) on building capacity to assess and respond to global change impacts on selected watersheds. One major task objective is to assess interactions of global warming and UV exposure that are contributing to the observed coral bleaching and disease. Our lab is working with scientists at the NHEERL Gulf Ecology Lab to characterize UV exposure and effects at several coral reef sites. Other research in this task is examining the interactions between UV-induced breakdown of refractory organic matter in estuaries and coastal areas that enhance UV penetration into the water and concurrently form biologically-labile nitrogen-, phosphorus- and carbon-containing substances that stimulate productivity and microbial activity. This task also involves research in central Brazil that is part of the Large Scale Biosphere Atmosphere Experiment (LBA). The objectives of this project are to assess the impacts of land use and climatic changes on soil nutrient cycles and microbiota, trace gas exchange and water quality in the Brazilian cerrado. This work involves a close collaboration between EPA and a group of scientists from the Department of Ecology, University of Brasilia, Brazil. Other objectives of this task are to assess the interactions of land use and climate changes with the ecological functioning of streams in watersheds of the Piedmont region of the southestern U.S.
Description:
We use measurements of the concentration and stable carbon isotope ratio of individual microbial phospholipid fatty acids (PLFAs) in soils as indicators of live microbial biomass levels, broad microbial community structure, and microbial carbon source. For studies of soil organic matter (SOM) cycling, the PLFA d13C technique is easiest to apply in ecosystems that have undergone a vegetation change (e.g. from C3 to C4 photosynthetic pathway) at known times in the past. Using principal components analysis (PCA) of the PLFA profiles, we were able to detect differences in microbial community structure related to soil type (Oxisol vs Andisols), agricultural management (forest vs pasture vs sugarcane), and soil depth. The PLFA stable carbon isotope ratio measurements showed that the soil microbial community living in the very old, relatively carbon-poor Oxisol site switched over to C4 carbon under sugarcane cultivation much more quickly (half life about 10 years) than did the sugarcane soil microbial communities in the much younger, carbon-rich Andisol sites (half life about 40 years).