Soil emissions of N2O, NO, and CO2 in Brazilian Savannas: Effects of vegetation type, seasonality, and prescribed fires

Abstract

Using closed chamber techniques, soil fluxes of NO, N2O, and CO2 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 CO2 fluxes than fire regime (early dry season, middle dry season or late dry season burning). N2O 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−2 h−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−2 h−1) during a water‐addition experiment in unburned campo sujo, and to 1.0 ng NO–N cm−2 h−1 in unburned cerrado and 1.9 ng NO–N cm−2 h−1 in burned cerrado with the first rains. Low NO and N2O emissions, low nitrification rates, and the majority of inorganic N in the form of NH4+ all indicate a conservative N cycle in the cerrado. CO2 fluxes increased with the onset of the rainy season and after artificial water addition. The highest CO2 measured in the wet season was 6.3 μmol CO2 m−2 s−1 in burned campo sujo. During the dry season, soil respiration in burned and unburned treatments were similar (average flux = 1.6–2.3 μmol CO2 m−2 s−1). Differences between fire treatments of cerrado and campo sujo CO2 fluxes are attributed to differences in relative litter production and root activity.