A Pimary Study On Methane Consumption By Forest Soils From Different Zones And Its Controlling Factors

Anthropic activity has result in the increase of atmohpheric methaneconcentration and greenhouse effect.Forest soil is a great methane sink andcontributes significantly to the atmospheric methane budget. It is important to studythe methane consumption by forest soil and its influence factors for the purpose ofbalancing the methane in atmpsphere and taking measures for increasing the uptakecapability.Forest surface and profile soils were sampled under temperate, sub-tropical andtropical forests, which were respectively located in Changbai Mountain, DinghushanMountain and Xishuangbanna district in China. A series of laboratory incubationswere done to study the methane (CH₄) consumption by the soils at atmospheric andhigh concentration (about 40μL L^-1 CH₄) methane, and the differences in soilatmospheric CH₄ consumption in the presence and absence of approximately 20μLL^-1 C₂H₄ in the headspace. In addition, N fertilization was applicated in forest soil toassessing the effect of N fertilization on methane consumption in forest soils.Temperate forest soils showed a greater methane uptake potential than tropicaland subtropical forest. There was a larger consumption potential of CH₄, and a largermaximum oxidation rate of CH₄ (V_max) in surface temperate forest soils than insubtropical and tropical forest soils. The variation of a half saturation constant (K_m)for CH₄ oxidation in all the forest soils was much great, indicating that the CH₄oxidation characteristics are different under different sites and under differentvegetations at each site. Both factor analysis and regression analysis showed that soilwater/salt extractable organic carbon and nitrogen, and microbial biomass were themain factors influencing CH₄ consumption in the soils.Tree species, landuse and distance from the bole affect the methaneconsumption. The Korea Pine forest in Changbai Mountain showed a highconsumption rate both in atmospheric and high-concentration methane,and its V_maxand K_m indicated its great potential. Otherwise, rainforest surface soils showedhigher consumption rate than rubber forest and tea garden soils.Methane consumption by Upper soils (0-10cm) in Temperate forest profiles declined sharply.The maximum consumption rate in Korea Pine foest is at 0-2.5cmdepth, while birch forest and spruce forest are at 2.5-7.5cm depth.In the presence of ethylene (about 20μL L^-1 C₂H₄), the soil atmospheric CH₄consumption was inhibited by 83-100ï¼…, along with a maximal inhibition in tropicalsoils. In the presence of ethylene (about 20μL L^-1 C₂H₄), the soil atmospheric CH₄consumption in profile soils was inhibited by 77-100ï¼…, along with a maximalinhibition (100ï¼…) in tropical soils.Streptomycin sulfate inhibited methane consumption in tropical and temperateforest soil, while it promoted methane consumption in subtropical forest. Incomparison with the Changbai Mountain soils, Xishuangbanna forest surface soils aremore sensitive to the Streptomycin sulfate.Incubation of N fertilized surface (0-5.0cm) soils indicated that (NH₄)₂SO₄ andNH₄Cl inhibited both atmospheric and high-concentration methane consumption, andKNO₃ only inhibited the high-concentration methane consumption in pine forest soils.After N applications in situ, NH₄Cl showed a positive inhibition onhigh-concentration methane consumption by surface(0-7cm) soils. But to all thefertilized organic soils from PVC tubes, NH₄Cl had a great inhibiton onhigh-concentration methane consumption, while (NH₄)₂SO₄ only had the same effecton 2-month fertilized organic soils in PVC tubes. The addition of KNO₃, K₂SO₄ andKCl inhibited methane comsumption, hence Cl^- and SO₄^2- is a inhibitor to methaneconsumption. Hence, the inhibition of fertilizer attributes to the inhibition of bothNH₄⁺(NO₃^-) and anions. HNO₃, H₂SO₄ and HCl inhibited high-concentration methaneconsumption in surface forest soils (0-5cm). Within a pH range of 4.9-5.4, therainforest methane consumption decrease with the decline of pH. When high does ofH₂SO₄ and HCl applied, N addition didn't enhance the inhibiton on methaneconsumption. It can be concluded that when both high doses of acid and N fertilizersapplied, the inhibition mainly attributed to acids.