EFFECTS OF MOISTURE AND BURNING ON SOIL-ATMOSPHERE EXCHANGE OF TRACE CARBON GASES IN A SOUTHERN AFRICAN SAVANNA

Soil fluxes of carbon dioxide (CO2), methane (CH4), and carbon monoxid e (CO) were measured during a period of extreme drought at semi-arid s avanna sites located in the Kruger National Park (KNP), South Africa, as part of the SAFARI-92 experiments (Sept., 1992). Soil respiration i n this savanna was little affected by burning, but was strongly stimul ated by addition of moisture. Mean soil respiration from the dry soil was 0.4 g C m(-2) d(-1) in open savanna plots that had been burned bie nnially and 0.5 g C m(-2) d(-1) in woody savanna plots. A light natura l rain (about 0.6 mm) increased the CO2 flux in the open savanna sites by 5-fold but the effect was short-lived. A simulated heavy rain (25 mm of added distilled water) increased CO2 fluxes by over an order of magnitude in both burned and control sites and the emissions remained over 5 times pre-wetting values during a week of drying. Over 65% of o ur measurements indicated no significant soil-atmosphere methane excha nge; most of the few non-zero measurements indicated a small (<1 mg CH 4-C m(-2) d(-1)) flux of methane to the atmosphere. Soil-atmosphere CH 4 exchange was not significantly affected by either burning the grass layer or by the addition of distilled water to the soil. The net soil CO fluxes, which generally increased with increasing soil temperature, were positive up to 356 x 10(9) molecules cm(-2) s(-1) with an averag e of 8.8 x 10(10) molecules cm(-2) s(-1) for the untreated open savann a plots. After burning, the fluxes rose by over an order of magnitude but dropped back to preburn levels within a few days. Observed CO flux es were higher than those previously reported for southern Africa sava nnas during non-drought conditions. Added moisture had little effect o n CO fluxes during the 3-week period of SAFARI-92.