ABSTRACT: To assess contribution of multiple environmental factors to actual carbon exchanges between the atmosphere and forest soils, four old-growth forests referred to as boreal coniferous forest, temperate needle-broadleaved mixed forest, subtropical evergreen broadleaved forest and tropical seasonal rain forest were selected along the eastern China. In each old-growth forest, soil CO2 and CH4 fluxes were measured for three years using the static chamber and gas chromatography technique. Soil temperature and moisture at the 10 cm depth were measured simultaneously with the greenhouse gas measurements. Inorganic N (NH4+-N and NO3--N) in the 0–10 cm was determined monthly. From north to south, annual mean CO2 flux ranged from 18.09±0.22 to 35.40±2.24 Mg CO2 ha−1 yr−1 and annual mean CH4 flux ranged from -0.04±0.11 to -5.15±0.96 kg CH4 ha−1 yr−1. Soil CO2 fluxes in the old-growth forests were mainly driven by soil temperature, followed by soil moisture and NO3--N. Based on the gradient theory of exchange of time and space, increase in air temperature in the future would promote soil CO2 emission in the old-growth forests. The responses of soil CH4 uptake to warming were dependent upon the critical temperature in forest. In addition, the NO3--N promotion to CO2 emission could partially attribute to the compound effects of high nitrate stimulation on soil microbe activities and increased decomposability of organic materials. The mechanism of NH4+ inhibition to CH4 uptake included both a competitive inhibition of CH4 mono-oxygenase enzyme and a toxic inhibition by hydroxylamine or nitrite produced via NH4+ oxidation. Overall, increasing in precipitation and nitrogen deposition in eastern China would increase soil CO2 emission, but decrease soil CH4 uptake in the old-growth forests.
Biogeosciences Discussions. 01/2009;