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EFFECT OF MANAGEMENT PRACTICES ON THE SOIL MICROBIAL COMMUNITY IN AGRICULTURAL AND NATIVE SYSTEMS IN BRAZIL
Citation:
Molina, M, L. Viana, R A. Burke Jr., M. Bustamante, AND R G. Zepp. EFFECT OF MANAGEMENT PRACTICES ON THE SOIL MICROBIAL COMMUNITY IN AGRICULTURAL AND NATIVE SYSTEMS IN BRAZIL. Presented at American Society for Microbiology Annual Meeting, New Orleans, LA, May 23-27, 2004.
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:
Increase in agricultural practices in the Cerrado (tropical savannah) and Amazon regions in Brazil is causing drastic changes in the nutrient and carbon cycling of native areas. Because microorganisms play a key role in biogeochemical cycling, monitoring the shifts in the microbial community structure may provide information about the nutrient and carbon dynamics in these ecosystems. We compared microbial communities under a range of management practices which included different native areas (savannah and forest), a pasture site, and a Cerrado area subjected to fertilization treatments (N, P, N+P, Ca) using phospholipid fatty acid analysis (PLFAs) and fungal to bacterial ratios. Fertilizers were applied after 10, 20 and 40 days to four plots (15 x15m) per treatment in a completely randomized design. Although the total PLFA concentration did not show significant differences among the sites, principal component analysis indicated that the structure of the microbial community varied as a function of the fertilization treatment and management practice (p<0.0001). In the fertilization experiment, Ca and the control treatment exhibited basically the same community structure and had a higher concentration of Gram negative biomarkers, while N, P, and N+P treatments had a higher concentration of Gram positive biomarkers and similar microbial communities. P amendments produced a higher fungal:bacterial ratio after 10 days of fertilization and was the only treatment showing a significant difference in the ratios. Fungal:bacterial ratios were also significantly higher in the pasture site when compared to the ratios observed in the native savannah and Amazon soils. The higher ratio in the pasture site correlated with lower availability of nitrogen and was a function of a decrease in the % composition of bacterial PLFAs. The fungal biomarker (18:2w6) maintained the same % composition across sites. The results suggest a phosphorus limitation on the fungal community inhabiting native Cerrado soils, while in pastures, nitrogen seems to limit the bacterial community, but has no effect on the fungi. Addition of N and P shifts the microbial community, increasing the concentration of Gram positive bacteria.