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STRUCTURE OF MICROBIAL COMMUNITIES IN NATIVE AND CONVERTED SAVANNA AREAS OF CENTRAL BRAZIL
Citation:
Viana, L., A. Pinto, M. Bustamante, M Molina, R G. Zepp, AND K. Kisselle. STRUCTURE OF MICROBIAL COMMUNITIES IN NATIVE AND CONVERTED SAVANNA AREAS OF CENTRAL BRAZIL. Presented at American Society for Microbiology Annual Meeting, Salt Lake City, UT, May 19-23, 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:
Brazilian savannas (Cerrado) have suffered drastic changes in land use with major conversion of native areas to agriculture since 1960. Burning, both due to natural conditions and as a human-induced practice, is a common event during the dry season (April to September) and plays a significant role in the conversion of areas. Although microorganisms have an important role in nutrient cycling and ecosystem functioning, the effect of land-use changes on microbial community structure and function is not well understood. We studied the effect of vegetation changes and fire regimes on the structure and dynamic of soil microbial communities using phospholipid fatty acid (PLFA) analysis. Soil samples (0-5cm) were collected from June/00 to June/01in two native areas subjected to different fire regimes (2 plots protected from fire since 1992 and 2 plots submitted to prescribed fires) and in an old, active pasture (Brachiaria brizantha). Total PLFA ranged from 0.21 to 27.82 ug/g wet weight with the lower values determined during the dry season. Principal component analysis (PCA) separated microbial communities by vegetation type (native vs. pasture) and seasonality (wet vs. dry), explaining 34% and 13%, respectively, of the total PLFA variability. No significant difference was observed in the communities extracted from the two native areas regardless of the difference in vegetation cover or between the burned and unburned plots. Gram negative bacteria (16:1w7c, 16:1w5, 18:1w7c) were in higher concentrations in the pasture than in native areas, which were dominated by lipids with an eukaryotic origin and a type of Gram positive bacteria. Cy19:0 and 10Me16:0 explained most of the variability during the dry season while eukaryotic lipids explained most of the variability during the wet season. The data indicate a strong effect due to land conversion and no effect due to burning regimes in the structure of soil microbial communities.