CARBON-MONOXIDE FLUXES OF DIFFERENT SOIL LAYERS IN UPLAND CANADIAN BOREAL FORESTS

Dark or low-light carbon:monoxide fluxes at upland Canadian boreal for est sites were measured on-site with static chambers and with a labora tory incubation technique using cores from different depths at the sam e sites. Three different upland black spruce sites, burned in 1987, 19 92 and 1995 and a control site, were chosen to determine the effects o f fire, temperature, soil structure and soil covers on CO fluxes. Thre e different surfaces were observed at the sites bare mineral soil with little living moss cover; burned feather mosses 5-30 cm deep; and unb urned, living, green feather mosses. The static chamber measurements i ndicated similar deposition velocities for the burned and unburned fea ther moss sites [(1.54+/-0.64) .10(-2) cm s(-1); (1.83 +/- 0.63).10(-2 ) cm s(-1)], but significantly lower rates for sites that had burned d own to the mineral soil [(1.08 +/- 0.53).10(-2) cm s(-1), excluding da ta with net CO emission]. This finding was confirmed by results from t he incubation measurements and shows that fire intensities determine t he long-term, post-fire effect on soil-atmosphere fluxes of CO. Temper ature studies with the cores showed that CO consumption rates increase d from (2 +/- 1)% at -15 degrees C to -13 degrees C to (43 +/- 20)% at 0 degrees C to 1.5 degrees C and (68 +/- 15)% at 4 degrees C to 5 deg rees C of the deposition velocity values obtained at 20 degrees C. Thi s temperature dependence was consistent with results obtained from the static chamber measurements. The temperature range studied and the da rk or low-light conditions were representative for the night-time of n early the whole six snow-free months in the boreal ecosystem. In nearl y all cases, deposition velocities determined for cores from the top 5 cm with the incubation technique were the same, within experimental e rrors, as those determined with the static chambers. Soil CO concentra tion profiles taken in situ, moreover, did not show any clear trend be low 5 cm. Thus we conclude that the top 5 cm of soils are determining the dark soil-atmosphere CO fluxes at these sites. The top 5 cm of soi l columns are most exposed to temperature (and probably moisture) vari ations and are most affected by fires as well.