Seasonal soil fluxes of carbon monoxide in burned and unburned Brazilian savannas

Soil-atmosphere fluxes of carbon monoxide (CO) were measured from September 1999 through November 2000 in savanna areas in central Brazil (Cerrado) under different fire regimes using transparent and opaque static chambers. Studies focused on two vegetation types, cerrado stricto sensu (ss) (20-50% canopy cover) and campo sujo (open, scrubland), which were either burned every 2 years or protected from fire (for 26 years). CO emissions in transparent chambers varied seasonally, with highest fluxes during the late dry season and transition to wet season (August-October) and lowest fluxes late in the wet season (February-April). Daytime fluxes in the transparent chambers were always higher than in the opaque chambers. Similarly, a diurnal study showed negative fluxes for all nighttime measurements and positive measurements for all daytime measurements made with transparent chambers. Deposition velocities observed in the opaque chambers during the night fell in the 0.002-0.0014 cm s(-1) range, which is at the lower end of the range that has been observed in tropical, temperate, and high-latitude regions. No significant differences were found between the daytime annual average fluxes from unburned cerrado and unburned campo sujo (160 x 10(9) and 190 x 10(9) molecules cm(-2) s(-1), respectively). Fire increased soil surface CO emissions significantly in the burned cerrado plot. Measurements made 30 days after the fire showed daytime CO production over 10 times higher than that of the unburned cerrado ss (812.8 x 10(9) versus 76.8 x 10(9) molecules cm(-2) s(-1)). Postfire CO emissions were greater than prefire emissions for both opaque and transparent chambers. However, the fire-induced increase was greater in the transparent chambers. This suggests that the fire created both photochemically and thermally reactive precursors. Removal of litter and standing, dead plant material from plots in unburned campo sujo and a pasture was shown to dramatically decrease CO emissions. CO production in burned plots (using opaque chambers) was similar to previous measurements from Venezuelan and African savannas.