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

Using closed chamber techniques, soil fluxes of NO, N 2 O, and CO 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 2 fluxes than fire regime (early dry season, middle dry season or late dry season burning). N 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 −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 N 2 O emissions, low nitrification rates, and the majority of inorganic N in the form of NH 4 + all indicate a conservative N cycle in the cerrado. CO 2 fluxes increased with the onset of the rainy season and after artificial water addition. The highest CO 2 measured in the wet season was 6.3 μmol CO 2 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 CO 2 m −2 s −1 ). Differences between fire treatments of cerrado and campo sujo CO 2 fluxes are attributed to differences in relative litter production and root activity.