华北人工林水热碳通量环境影响因子分析

Environmental controls over energy, water and carbon fluxes in a plantation in Northern China

基于河北崇陵流域人工林涡度相关通量观测数据,采用通径分析和分段回归解析了水热碳通量与土壤水分、饱和水汽压差、空气和土壤温度,及净辐射、光合有效辐射等环境因子的关联性。结果表明,通径分析法揭示了各指标的主导/次要因子的直接及间接效应,显热通量和水分利用效率的主要影响因子为饱和水汽压差,而潜热通量、碳通量的影响因子以辐射、温度为主;分段回归法进一步探讨了次要因子对主导因子的限制作用,当0.20 m3·m–3<土壤水分含量≤0.35 m3·m–3时,潜热通量、生态系统呼吸及水分利用效率与其主导因子间相关性最高,当饱和水汽压差≤1.0 k Pa时,净生态系统生产力、总生态系统生产力与其主导因子间相关性最高;两种方法的有机结合,使我们对生态水文过程各驱动因子有了清晰的宏观认识,并量化了次要因子起限制作用的数量范围。

Aims Our objective was to examine the underline mechanisms on the driving factors of eco-hydrological processes and identify the limiting factors through both path analysis and piecewise regression.Methods The eddy covariance and meteorological data of a plantation in Chongling watershed in Northern China over the period from August 2012 to August 2013 were used for analyzing the relationships between flux indices and environmental factors. The flux indices include sensible heat, latent heat, net ecosystem production, gross ecosystem production, and ecosystem respiration, and the environmental factors include soil water content, vapor pressure deficit, air temperature, soil temperature, net radiation and photosynthetically active radiation. The direct and indirect effects of dominant and secondary factors were determined through the path analysis, and the control of secondary factors on dominant factors were analyzed using the piecewise regression.Important findings We found that the primary factor affecting sensible heat and water use efficiency was vapor pressure deficit, while latent heat and carbon fluxes were mainly controlled by radiation and temperature respectively. There also appeared significant influences from secondary variables on those fluxes. The correlations between latent heat and net radiation, ecosystem respiration and soil temperature, and water use efficiency and vapor pressure deficit were all strong when soil water content was between 0.20 m^3·m^-3 and 0.35 m^3·m^-3. The correlations between ecosystem production （both gross and net） and photosynthetically active radiation was strong when vapor pressure deficit was ≤1.0 kPa.