Temperature as a control over ecosystem CO2 fluxes in a high-elevation, subalpine forest
Temperature as a control over ecosystem CO2 fluxes in a high-elevation, subalpine forest
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DOI：
10.1007/s00442-002-1131-1
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发表时间：
2003-03-01
期刊：
影响因子：
2.7
通讯作者：
Monson, RK
中科院分区：
文献类型：
--
作者：
Huxman, TE;Turnipseed, AA;Monson, RK
我们评估了亚高山针叶林的二氧化碳吸收受生长季节低温限制的假设。利用涡旋相关法对两个生长季节的生态系统净CO2交换（NEE）进行了观测。在两个年份的整个生长季节，光饱和生态系统净CO2交换（NEEsat）在7 ~ 12℃范围内表现出最优温度。生态系统呼吸速率（Re），即NEE与光合光子通量密度（PPFD）关系的y截距，随着温度的升高而增加，导致该生态系统的净二氧化碳吸收能力减少15%，从典型的季节早期温度7℃上升到典型的季节中期温度18℃。衡量光利用效率的生态系统量子产量和生态系统PPFD补偿点在季初低温时最高，在季末高温时降低。树枝水平的测量结果表明，三种优势针叶树的净光合作用在季节早期和季节后期分别在10℃和15℃左右表现出最佳温度。通过通径分析，将温度作为季节变量进行统计分离，确定了温度在季节前期和后期对生态系统通量的动态控制作用。在春季，温度的升高对NEE有积极的影响，因为白天温度从接近冰点到接近最适光合温度，Re值保持在较低水平。在夏季中期，温度的升高会抑制净光合作用和Re的增加，从而对NEE产生负面影响。综合考虑这些结果，结果表明，在这个高海拔森林生态系统中，二氧化碳的吸收并不像以前在树枝和针叶水平上的一些生态生理研究所表明的那样，在生长季节受到低温对光合过程的限制。相反，正是盛夏的温暖气温及其对生态系统呼吸的影响，导致了森林碳固存潜力的最大减少。
We evaluated the hypothesis that CO2 uptake by a subalpine, coniferous forest is limited by cool temperature during the growing season. Using the eddy covariance approach we conducted observations of net ecosystem CO2 exchange (NEE) across two growing seasons. When pooled for the entire growing season during both years, light-saturated net ecosystem CO2 exchange (NEEsat) exhibited a temperature optimum within the range 7-12degreesC. Ecosystem respiration rate (Re), calculated as the y-intercept of the NEE versus photosynthetic photon flux density (PPFD) relationship, increased with increasing temperature, causing a 15% reduction in net CO2 uptake capacity for this ecosystem as temperatures increased from typical early season temperatures of 7degreesC to typical mid-season temperatures of 18degreesC. The ecosystem quantum yield and the ecosystem PPFD compensation point, which are measures of light-utilization efficiency, were highest during the cool temperatures of the early season, and decreased later in the season at higher temperatures. Branch-level measurements revealed that net photosynthesis in all three of the dominant conifer tree species exhibited a temperature optimum near 10degreesC early in the season and 15degreesC later in the season. Using path analysis, we statistically isolated temperature as a seasonal variable, and identified the dynamic role that temperature exhibits in controlling ecosystem fluxes early and late in the season. During the spring, an increase in temperature has a positive effect on NEE, because daytime temperatures progress from near freezing to near the photosynthetic temperature optimum, and Re values remain low. During the middle of the summer an increase in temperature has a negative effect on NEE, because inhibition of net photosynthesis and increases in Re. When taken together, the results demonstrate that in this high-elevation forest ecosystem CO2 uptake is not limited by cool-temperature constraints on photosynthetic processes during the growing-season, as suggested by some previous ecophysiological studies at the branch and needle levels. Rather, it is warm temperatures in the midsummer, and their effect on ecosystem respiration, that cause the greatest reduction in the potential for forest carbon sequestration.