皆伐火烧对亚热带森林不同深度土壤CO_2通量的影响

The impact of clear-cutting and slash burning on soil CO_2 flux at different soil depths in a subtropical forest

评估不同深度土壤的CO_2通量是研究土壤碳动态的重要手段。目前有关皆伐火烧对森林土壤碳排放的影响研究仅局限于表层土壤,而对不同深度土壤碳排放影响鲜见报道。以米槠(Castanopsis carlesii)次生林(对照)及其皆伐火烧后林地为研究对象,利用非红外散射CO_2探头测定土壤CO_2浓度,并结合Fick第一扩散法则估算不同深度(0—80 cm)土壤CO_2通量。结果表明:(1)皆伐火烧改变土壤向大气排放的表观CO_2通量,在皆伐火烧后的2个月内土壤表观CO_2通量显著高于对照68%;2个月后,土壤表观CO_2通量低于对照37%。(2)皆伐火烧后,除10—20 cm的CO_2通量提高外,其余各深度(0—10、20—40、40—60 cm和60—80 cm)的CO_2通量均降低。同时,皆伐火烧改变不同土层对土壤呼吸的贡献率,降低0—10 cm土层的贡献率,提高10—20 cm土层的贡献率。(3)对照样地仅0—10 cm土壤CO_2通量与温度呈显著指数相关,10—40 cm深度CO_2通量则与土壤含水率呈显著线性相关。皆伐火烧后0—10 cm和10—20 cm处土壤的CO_2通量均与温度呈指数相关。说明皆伐火烧改变了不同深度土壤CO_2通量对于环境因子的响应。因此为准确评估和预测皆伐火烧对土壤与大气间碳交换的影响,应考虑皆伐火烧后不同时期土壤CO_2通量的变化,以及不同深度土壤CO_2通量对皆伐火烧的响应。

Soil CO2 flux at different depths is an important means of researching the soil carbon dynamics. At present, the impacts of clear-cutting and slash burning on forest soil carbon emissions focus on surface soil, while their impacts on soil carbon emissions at different depths are not well known. In this study, CO2 flux along a soil profile （0-80 cm） was measured in an uncut secondary Castanopsis carlesii forest （CT） and a clear-cut, slash burnt （SB） stand of Castanopsis carlesii located in Sanming, Fujian. A scattered infrared CO2 detector was used to measure soil CO2 concentration, combined with Fick＇s laws of diffusion to estimate soil CO2 flux at different depths. Results showed that, （1） SB changed the apparent CO2 flux significantly. Within two months after SB, the soil surface CO2 flux increased by 68%. However, the soil surface CO2 flux decreased by 37% two months later. （2） After SB, soil CO2 fluxes at depths of 0-10, 20-40, 40-60 cm and 60-80 cm decreased with the exception of an increase at a depth of 10-20 cm. In the meantime, SB decreased the contribution rate of CO2 flux in the 0-10 cm soil layer, and increased the contribution rate of CO2 flux in the 10-20 cm soil layer. （3） There was an exponential relationship between soil CO2 flux at 0-10 cm and temperature, and the soil CO2 fluxes at other soil depths were linearly correlated with soil moisture in the control plot. After SB, soil CO2 fluxes at depths of 0-10 cm and 10-20 cm were exponentially correlated with soil temperature, which illustrated that SB changed the soil CO2 flux response at different depths due to environmental factors. Thus, in order to estimate and predict the impact of clear-cutting and SB on carbon exchange between soil and the atmosphere accurately, it is necessary to consider the changes in soil CO2 flux during different periods after SB and the response of soil CO2 flux to SB at different depths.