荒漠冻融期积雪变化对生物结皮甲烷通量的影响

Effect of snow cover variation on methane flux in biocrusts during desert freezing-thawing period

温带荒漠积雪覆盖是土壤含水量增加的重要方式,在冻融期带来丰富的水分变化。全球气候变化导致温带荒漠积雪深度时空格局发生改变,从而影响荒漠生态系统温室气体的通量。生物结皮在维持荒漠生态系统结构和功能的稳定具有非常重要的作用,但对环境的变化较为敏感,尤其是降水变化。然而,目前有关冻融期不同积雪条件下生物结皮温室气体通量的研究十分匮乏。CH4是重要的温室气体,选择古尔班通古特沙漠藓和地衣2种类型生物结皮为研究对象,以裸沙为对照,设置增雪、自然降雪(对照)和除雪三种处理,通过静态箱-气相色谱法,探究CH4通量在冻融期的变化特征。结果表明:冻融期多数情况下积雪处理和结皮类型对CH4通量影响不显著。荒漠生物结皮对CH4整体表现为吸收作用,是荒漠生态系统CH4重要的“汇”。两种结皮类型及裸沙CH4的吸收速率呈现为地衣结皮(-10.12μg m^(-2) h^(-1))>藓结皮(-1.73μg m^(-2) h^(-1))>裸沙(-1.69μg m^(-2) h^(-1))。CH4通量通常与土壤5 cm深处的温度和水分的相关性不显著,对其他土壤理化因子响应较弱。研究结果表明,积雪处理不会对冻融期生物结皮CH4通量产生显著影响,全球变化条件下温带荒漠积雪的改变可能对土壤CH4的产生和吸收影响较小。

Snow cover is an important way to increase soil moisture content in temperate desert,which can provide abundant water during the freezing-thawing period.Changes in spatial and temporal patterns of snow depth under global changes in temperate deserts affect greenhouse gas flux in desert ecosystems.Biological soil crusts(biocrusts)play crucial role in stability of structure and function of desert ecosystem,while they are sensitive to environmental changes,especially to precipitation changes.However,few studies on greenhouse gas fluxes were found in desert biocrusts during freezing-thawing period under snow treatments.CH4 is an important greenhouse gas.In this study,two types of biocrusts,moss and lichen crusts were selected,and bare sand was as control.Three snow cover treatments,including snow addition,natural snow(control)and snow reduction were conducted.We aimed to explore the variation in CH4 flux in 2019 and 2021 during freezing-thawing period based on static chamber-gas chromatography.In general,snow treatment and crust types had no significant effects on CH4 flux.Desert biocrusts generally absorbed CH4 in this study,and were important“sinks”of CH4 in desert ecosystems.The absorption rates of CH4 for the two types of crusts and bare sand were lichen crusts(-10.12μg m^(-2) h^(-1))>bare sand(-1.73μg m^(-2 )h^(-1))>moss crusts(-1.69μg m^(-2) h^(-1)).CH4 fluxes were generally not significantly correlated with soil temperature and water content at 5 cm depth,and had weak response to other soil physicochemical factors.The results showed that snow cover treatments had no significant effects on CH4 flux in biocrusts during freezing-thawing period,and the change in snow cover in temperate desert may have few effects on CH4 production and absorption in soil under the condition of global change.