NO fluxes from savannas of Central Brazil (Cerrado) subjected to nitrogen and phosphorus fertilization
Alessandra
Rodrigues
Kozovits, Universidade de Brasília, kozovits@unb.br
(Presenting)
Laura
Tillman
Viana, Universidade de Brasília, lviana@unb.br
Danielle
Matias
Souza, Universidade de Brasília, daniellematias@yahoo.com.br
Alexandre
de S.
Pinto, Universidade de Brasília, alexandrep@ftb.br
Mercedes
Maria Cunha
Bustamante, Universidade de Brasília, mercedes@unb.br
The Cerrado biome covers 2 million km2, quite as large as Western Europe. It is a species rich wet tropical savanna classified as a hotspot of its large number of endemic species and the vulnerability of this ecosystem. The soils are generally highly weathered and trees and shrubs may present deep root systems. In spite of seasonal rainfall distribution part of the woody vegetation is evergreen. Therefore Cerrado has an important role regulating the regional hydrological cycle. The fragmentation of Cerrado areas and the rapid conversion into agroecosystems may lead to higher nutrient inputs in adjacent native areas. Our objective was to determine the effects of long-term nutrient addition (N and N+P) in native Cerrado area on N oxides fluxes from soil to the atmosphere. The experiment was established at Ecological Reserve of the IBGE, 35 km south of Brasília, Brazil. 12 plots of 15 m x 15 m were randomly delimited with 4 replicates per treatment: (Control): without fertilization, (+N): ((NH4)2SO4) = 100 kg N ha-1 year -1 and (+NP): 100 kg N ha-1 year -1+ 100 kg P ha-1 year -1. Plots were fertilized every year since 1998. Flux measurements of NO and N2O were taken in March 2004 before the fertilization of this year. High NO soil emissions were measured in the +N plots (6.5 ng NO cm-2 h-1), although the last fertilization occurred one year ago. Interestingly, NO emissions in the +NP plots were about 12 times lower than those of +N and similar to the values found in non-fertilized Cerrado areas (0.55 ng NO cm-2 h-1). Generally, N2O was under the detection limit (0.6 ng N2O cm-2 h-1). These results indicate that NO emissions from native cerrado areas are not only influenced by N availability but also by the P availability. The addition of P would enhance N assimilation and retention by plants and less nitrogen would be release by the ecosystem as NO.