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ND-07 Abstract

Impacts of Land Use Change on Nutrient and Carbon Cycles and Trace Gas Exchange in Soils of Savannas of Central Brazil

Mercedes Bustamante — UnB - Universidade de Brasília (SA-PI)
Richard G. Zepp — US EPA (US-PI)


The proposed studies will focus on the effects of fire and land use change on the

composition and persistence of litter and soil organic carbon and nitrogen and related

changes in the soil-atmosphere fluxes of carbon dioxide, carbon monoxide, nitrous oxide,

and nitric oxide. The studies are proposed for a range of cerrado types and agroecosystems

in the area surrounding Brasilia. We will quantify rates of carbon and nutrient cycling

and characterize SOM at sites ranging from undisturbed cerrado to burned cerrado to

agroecosystems. These experiments will include measurements of the carbon and nitrogen

content and stable isotope ratios of the litter and SOM isolated by size and physical

fractionation. The lignin content and concentrations of UV-absorbing compounds of the

litter will also be measured. To determine the size and diversity of the soil microbial

community at the sites, we will measure the amount and composition of biomarker compounds

in the litter and SOM, particularly phosopholipid ester-linked fatty acids (PLFA) and

ergosterol. For ecosystems that have undergone a vegetation change (e.g., from C3

dominated closed canopy cerrado to C4 pasture) we will measure the carbon

isotopic composition of individual PLFAs to indicate the source(s) of carbon being

actively metabolized by the microbial community. To provide data and relationships needed

for regional trace gas models, we will measure soil-atmosphere fluxes of trace carbon and

nitrogen gases (CO2, CO, N2O NO) under various natural (e.g. along

transects) and manipulated conditions. Ancillary data relevant to these studies will also

be obtained, including changes in soil temperature, moisture, and incident solar radiation

that accompany land use change and subsequent agricultural uses of the cleared land.

Limited manipulations will be conducted during the dry season at the cleared sites, e.g.

pasture, to measure the effects of solar UV-B exclusion on fluxes of the trace gases from

the surface litter and dead grasses.

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