Effects of multiple environmental factors on CO2 emission and CH4 uptake from old-growth forest soils

[摘要] To assess contribution of multiple environmental factorsto carbon exchanges between the atmosphere and forest soils, four old-growthforests referred to as boreal coniferous forest, temperateneedle-broadleaved mixed forest, subtropical evergreen broadleaved forestand tropical monsoon rain forest were selected along eastern China. In eachold-growth forest, soil CO₂ and CH₄ fluxes were measured from 2003to 2005 applying the static opaque chamber and gas chromatography technique.Soil temperature and moisture at the 10 cm depth were simultaneouslymeasured with the greenhouse gas measurements. Inorganic N (NH₄⁺-Nand NO₃⁻-N) in the 0–10 cm was determined monthly. From north tosouth, annual mean CO₂ emission ranged from 18.09 ± 0.22 to35.40 ± 2.24 Mg CO₂ ha⁻¹ yr⁻¹ and annual mean CH₄uptake ranged from 0.04 ± 0.11 to 5.15 ± 0.96 kg CH₄ ha⁻¹ yr⁻¹in the four old-growth forests. Soil CO₂ flux in theold-growth forests was mainly driven by soil temperature, followed by soilmoisture and NO₃⁻-N. Temperature sensitivity (Q₁₀) of soilCO₂ flux was lower at lower latitudes with high temperature and moreprecipitation, probably because of less soil organic carbon (SOC). SoilNO₃⁻ accumulation caused by environmental change was oftenaccompanied by an increase in soil CO₂ emission. In addition, soilCH₄ uptake decreased with an increase in soil moisture. The response ofsoil CH₄ flux to temperature was dependent upon the optimal value ofsoil temperature in each forest. Soil NH₄⁺-N consumption tended topromote soil CH₄ uptake in the old-growth forests, whereas soilNO₃⁻-N accumulation was not conducive to CH₄ oxidation inanaerobic condition. These results indicate that soil mineral N dynamicslargely affects the soil gas fluxes of CO₂ and CH₄ in theold-growth forests, along with climate conditions.

[学科分类] 地球化学与岩石