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SOIL EMISSIONS OF CO2 AND CO IN TROPICAL SAVANNAS OF CENTRAL BRAZIL UNDER DIFFERENT FIRE REGIMES
Citation:
Pinto, A., M. Bustamante, L. Viana, R G. Zepp, R A. Burke Jr., M Molina, AND K. Kisselle. SOIL EMISSIONS OF CO2 AND CO IN TROPICAL SAVANNAS OF CENTRAL BRAZIL UNDER DIFFERENT FIRE REGIMES. Presented at Large Scale Biosphere-Atmosphere Experiment in Amazonia Open Meeting, Atlanta, GA, February 12-14, 2001.
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:
The Cerrado is a tropical savanna in which herbaceous vegetation (mainly C4 grasses) coexists with trees and shrubs. It covers more than two million square kilometers and accounts for 22% of the total area of Brazil. In general, cerrado soils are old, deep, well drained, well structured, acidic, have low fertility, and high iron and aluminum contents. Mean rainfall is 1500 mm per year with well-defined wet and dry seasons. The term Cerrado represents three general physiognomic types of vegetation reflecting variation in degree of tree cover: campo sujo (open, grass-dominated), cerrado stricto sensu (ss) and cerrado (closed forest). In campo sujo <10% of the soil surface is shaded, whereas in the closed forest >90% of the soil surface is shaded. The degree of soil shading in cerrado ss ecosystems is intermediate between that of campo sujo and cerrado. Extensive areas of Cerrado have been converted to pastures and grasslands by frequent burning or clearing. Our objective was to assess the soil fluxes of CO2 and CO in Cerrado areas subjected to prescribed fires. Biological production of CO2 in soils is derived from the decomposition of soil organic matter and from root respiration. CO is produced by photodegradation of litter and it can be consumed by microbial activity. The studies are focusing on two classes of Cerrado, campo sujo and cerrado ss, located at the research and ecological reserve operated by IGBE, 35 km south of Brasilia (15o56'S, 47o53'W). The burned areas have been subjected to prescribed fires every two years since 1992 at the end of the dry season (late September). The unburned areas have been protected from fire for the last 26 years. A water addition experiment at unburned campo sujo was carried out in August 2000 (middle of dry season). The soil of the campo sujo areas is classified as Latossolo Vermelho-Amarelo (red-yellow Latosols, Brazilian Soil Classification) while Latossolo Vermelho-escuro (dark-red Latosols) are found in the cerrado ss. The measurements have been carried out since September 1999. The input of organic matter, microbial activity and soil moisture were pointed out as important variables affecting the soil respiration in Cerrado soils. The highest flux was found during the wet season (5.57 mol CO2 cm-2 s-1) and the lowest during the dry season (1.62 mol CO2 cm-2 s-1). On campo sujo plots, burned area showed high soil respiration on wet season (October 1999, April and September 2000) and on dry season there is no difference between burned and unburned areas. The grasses are more dominant in the burned area, and their roots could have an important contribution for soil respiration. The unburned cerrado showed higher soil respiration than burned cerrado and unburned campo sujo areas. The highest addition of organic matter on unburned cerrado could explain the higher soil respiration, and it contributes to higher activity of microorganisms. The addition of water during the dry season showed a stronger effect on soil respiration than the fire treatment. After 30 min of the water addition, the flux increased from 1.4 mol CO2 cm-2 s-1 to 6.6 mol CO2 cm-2 s-1, while no differences were observed before and after fire. The organic matter is also important for control of CO emissions. The unburned plots (high density of woody plants) showed the highest fluxes of CO. The main period of this production was on dry season, when the canopy was more open (higher UV incidence) and the amount of litter is high.