Forest Floor CO2 Flux From Two Contrasting Ecosystems in the Southern Appalachians
We measured forest floor CO2 flux in two contrasting ecosystems (white pine plantation and northern hardwood ecosystems at low and high elevations, respectively) in May and September 1993 to quantify differences and determine factors regulating CO2 fluxes. An automated IRGA based, flow through system was used with chambers inserted into the soil. This approach allowed quantification of diurnal flux patterns which were subsequently averaged to estimate daily mean flux rates (µmol m-2s-1). Mean flux rates were 60 percent greater in the white pine ecosystem (8.9 µmol m-2s-1) than in the northern hardwood ecosystem (5.6 µmol m-2s-1). Across ecosystems and sample dates, the most important regulating factor was soil temperature (r2 = 0.70; p < 0.0001). Mean (24-hr) soil temperature (at 5 cm depth) was 2.5°C lower in the northern hardwood stand relative to the white pine stand. All other parameters considered (i.e., soil C:N, root mass, root C:N, litter C:N, litter mass) did not explain the differences in flux rates between sites, but variation in fine root mass and litter C:N did explain spatial and temporal variation within the northern hardwood site. These results indicated that at large spatial scales, variation in soil temperature was more important in regulating forest floor CO2 flux than factors more closely associated with the species composition and productivity of the sites (e.g., litter and root mass and quality).