中亚热带杉木人工林苔藓覆盖对土壤温室气体排放的影响

Effects of moss mat on soil CO_2,CH_4 and N_2O fluxes in Cunninghamia lanceolata plantation in mid-subtropical region

目前,国内尚无亚热带森林地区生物土壤结皮-土壤系统温室气体通量特征的研究,给区域尺度上温室气体通量的估算带来很大的不确定性。本研究选择中亚热带杉木人工林中地面广布的苔藓覆盖形成的结皮层及其下覆土壤为研究对象,采用对气体排放速率影响较小的等压取样法,探究去除苔藓土壤(BG)和苔藓覆盖土壤(BSCs)在光照和暗处理下其温室气体通量的变化特征,来模拟自然环境下白昼和黑夜时段苔藓覆盖的影响,同时采用随机森林模型来衡量光照与苔藓覆盖对温室气体通量的重要度。结果表明:苔藓覆盖、光照处理及其互作对CO_2通量有极显著的影响(P<0.001),苔藓覆盖和光照处理对CH_4的吸收通量有极显著的影响(P<0.001),光照及光照与苔藓覆盖交互作用对N_2O通量有极显著的影响(P<0.001);暗处理下,与BG土壤相比,苔藓覆盖具有抑制土壤CO_2排放的趋势,苔藓覆盖略微增加N_2O的排放通量,但显著增加CH_4的吸收通量(P<0.01);光照处理下BSCs的CO_2、CH_4和N_2O三种温室气体均出现负通量,苔藓覆盖显著降低CO_2、CH_4和N_2O的排放通量(P<0.01),表明光照条件下苔藓-土壤系统是这三种温室气体重要的汇;由光照导致的BSCs的CO_2和N_2O的吸收通量显著高于BG土壤温室气体的吸收量(P<0.01),但光照对CH_4吸收通量的影响无显著差异;随机森林分析表明,光照对于CO_2和N_2O通量的影响的重要性大于苔藓覆盖,而苔藓覆盖对CH_4通量的影响的重要性大于光照,表明CO_2和N_2O的通量与苔藓中的光能自养生物的代谢活性关联更大,CH_4通量与苔藓中的化能自养生物代谢活性有关联。

No data are available on greenhouse gas flux characteristics of biological soil crust （BSCs） in subtropical forests, which brings great uncertainty for estimating the regional greenhouse gas fluxes. In this study, we investigated the patterns of CO2, CH4 and N2O exchange of BSCs and soils in condition of light or dark in a mid-subtropical Cunninghamia lanceolata plantation. Equal pressure sampling method was used to minimize the disturbance of soils. The gas samples were analyzed with gas chromatography （GC） （Shimadzu）. Random forest algorithm was used to compare the effects of light and BSCs on the fluxes of greenhouse gases. The results showed that BSCs, light and their interaction significantly affected CO2 flux （P〈0.001）. BSCs and light had significant effects on CH4 absorption flux （P〈0.001）. Light and its interaction with BSCs exerted significant effects on the N2O flux （P〈0.001）. Our results indicated that BSCs and light played important roles in soil greenhouse gas emissions in the study site. BSCs restrained soil CO2 emission under dark condition. BSCs slightly increased N2O flux and significantly increased CH4 absorption flux （P〈0.01）. Moreover, CO2, CH4 and N2O fluxes of BSCs were significantly decreased under light condition. Light had greater effect on CO2 and N2O flux than on BSCs, whereas BSCs had greater effect on CH4 flux than light. Such a result indicated that the CO2 and N2O fluxes were associated with the photoautotroph of BSCs while chemoautotroph played a great role in CH4 flux.