荒漠杜加依林冠层水热变化及CO_2交换特征

Carbon interfacial hydrothermal variation and CO_2 exchange characteristics of the Tugai forest in a desert environment

选取新疆艾比湖湿地国家级自然保护区荒漠杜加依林为研究对象,利用通量塔连续观测数据分析新疆艾比湖流域内杜加依林冠层界面水热垂直变化和CO_2交换特征,进一步比较了冠层界面湍流碳通量、植物冠层储存碳通量及净碳交换量,探讨了不同时间和垂直空间序列下杜加依林冠层界面温湿廓线与CO_2交换过程的相互关系。结果表明,新疆艾比湖流域内杜加依林冠层上方大气稳定度生长季的6—9月为中性(z/L=0.009),非生长季为不稳定(z/L=-0.449),全年总体呈不稳定水平(z/L=-0.194);冠层界面上气温垂直变幅小于5℃,随高度呈递增趋势,湿度垂直变幅超过40%;地-气碳通量呈秋冬小春夏大规律,年碳收支高于干旱区平均水平,为-0.026 mg CO_2m^(-2)s^(-1),表现为碳汇;垂直空间尺度上垂直温湿度差与生态系统净碳交换量(NEE,Net Ecosystem Exchange)拟合较好,温度拟合结果为R^2=0.7350(P﹤0.01),湿度拟合结果为R^2=0.3627(P﹤0.01),水热变点分别为5%和1℃,而季节尺度上温度拟合结果较好,温度拟合结果为R^2=0. 5221(P﹤0. 01),湿度拟合结果为R^2=0.1716(P﹤0.01),变点为55%和18℃。生长季较小的冠层垂直温差有利于杜加依林对大气CO_2的吸收,而冠层高湿环境则会抑制杜加依林对CO_2的吸收。

In the present study,the Tugai forest in the Ebinur Lake Wetland National Nature Reserve in Xinjiang,Northwest China was analyzed.Canopy interfacial hydrothermal vertical variation and CO2 exchange characteristics of the Tugai forest were analyzed using continuous data observed from a 30 m high flux tower in the study area,and the turbulent carbon flux at the canopy interface,plant canopy carbon flux,and net carbon exchange at the canopy interface were also compared.In addition,the relationship between the temperature and humidity profiles at the canopy interface and CO2 exchange process under different temporal and vertical spatial sequences were determined.The results showed that the atmospheric stability over the canopy layer during the growing season(from June to September)was neutral(z/L=0.009),but unstable during the non-growing season(z/L=-0.449),and also unstable(z/L=-0.194)almost throughout the year.The vertical amplitude of the air temperature at the canopy interface was<5℃,and air temperature increased with increasing canopy height;the vertical amplitude of humidity was>40%.The land-atmosphere carbon flux was low in autumn and winter and high in spring and summer.The annual carbon budget was-0.026 mg CO2 m^-2s^-1,which was higher than the average level of arid areas,and appeared to be a carbon sink.The vertical temperature and humidity differences on the vertical spatial scale fitted well to the net ecosystem carbon exchange capacity(NEE),with an R2 fitting coefficient of 0.7350(P﹤0.01)for temperature,and 0.3627(P﹤0.01)for humidity,and the hydrothermal inflection points were 5%and 1℃,respectively.However,the temperature fitting result was better seasonally,where R2 was 0.5221(P﹤0.01)for temperature and 0.1716(P﹤0.01)for humidity,and the hydrothermal inflection points were 55%and18℃,respectively.The smaller vertical temperature gradients in the canopy during the growing season would be beneficial to atmospheric CO2 absorption,whereas the high humidity environment of the canopy could inhibit the atmospheric CO2 uptake by the Tugai forest.