Soil emissions of N sub(2)O, NO, and CO sub(2) in Brazilian Savannas: Effects of vegetation type, seasonality, and prescribed fires

• Published in: Journal of Geophysical Research. D. Atmospheres Vol. 107; no. D20
• Main Authors: De Siqueira Pinto, A, Bustamante, MMC, Kisselle, K, Burke, R, Zepp, R, Viana, L T, Varella, R F, Molina, M
• Format: Journal Article
• Language: English
• Published: 27-10-2002
• ISSN: 0148-0227
• DOI: 10.1029/2001JD000342

Using closed chamber techniques, soil fluxes of NO, N sub(2)O, and CO sub(2) were measured from September 1999 to November 2000 in savanna areas of central Brazil (cerrado) subjected to prescribed fires. Our studies focused on two vegetation types, cerrado stricto sensu (20-50% canopy cover) and campo sujo (open, grass dominated), which were either burned every 2 years or protected from fire. Soil moisture and vegetation type were more important in controlling NO and CO sub(2) fluxes than fire regime (early dry season, middle dry season or late dry season burning). N sub(2)O fluxes, however, were very low and below detection limit in any of the vegetation-fire treatments. NO emissions increased after burning (1.0 ng NO-N cm super(-2) h super(-1)), but flux returned quickly to prefire levels and even lower. In comparison, NO emissions increased 100-fold (to 10.5 ng NO-N cm super(-2) h super(-1)) during a water-addition experiment in unburned campo sujo, and to 1.0 ng NO-N cm super(-2) h super(-1) in unburned cerrado and 1.9 ng NO-N cm super(-2) h super(-1) in burned cerrado with the first rains. Low NO and N sub(2)O emissions, low nitrification rates, and the majority of inorganic N in the form of NH sub(4) beta super(+) all indicate a conservative N cycle in the cerrado. CO sub(2) fluxes increased with the onset of the rainy season and after artificial water addition. The highest CO sub(2) measured in the wet season was 6.3 mu mol CO sub(2) m super(-2) s super(-1) in burned campo sujo. During the dry season, soil respiration in burned and unburned treatments were similar (average flux = 1.6-2.3 mu mol CO sub(2) m super(-2) s super(-1)). Differences between fire treatments of cerrado and campo sujo CO sub(2) fluxes are attributed to differences in relative litter production and root activity.