CO2 fluxes over an old, temperate mixed forest in northeastern China
CO2 fluxes over an old, temperate mixed forest in northeastern China
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DOI：
10.1016/j.agrformet.2006.02.003
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发表时间：
2006-04-14
影响因子：
6.2
通讯作者：
Jin, Chang-Jie
中科院分区：
文献类型：
--
作者：
Guan, De-Xin;Wu, Jia-Bing;Jin, Chang-Jie
对中国东北部一片温带混交林16个月来的二氧化碳交换进行了涡度协方差测量。该林分是一种自然生长的、未经管理的落叶阔叶林和针叶林的混合林，这些树木覆盖了广泛的年龄段，最高可达约450年。这项研究的目的是检验传统的假设，即森林在发育后期是微不足道的碳汇。在土壤水分充足的条件下，对生态系统的CO2交换进行了研究。主要研究结果如下：(1)生态系统呼吸及其组成部分，包括土壤呼吸、茎呼吸和叶呼吸，均与土壤或气温呈指数相关，但其占生态系统总呼吸的比例在年内变化较大。随着温度的升高，土壤呼吸占总呼吸的比例相对稳定，而叶和茎的呼吸分别增加和减少。土壤呼吸是最大的组成部分(平均占整个生态系统呼吸的48%，不包括倒下的树木和粗木质碎屑的呼吸)。叶呼吸作用次之(22-40%)，茎呼吸作用最小(13-29%)。(2)由于生长季环境因子充足，生态系统具有很大的同化潜力，但受水汽压亏缺(VPD)的影响，实际总生态系统交换(G(Ee))仅为潜力的45%左右。较高的VPD降低了叶片的光合作用能力，最大相对降幅出现在下午，此时VPD较高，相对降幅在0.3~0.6之间。5月和7月降幅较大，对应于VPD较高的2个月。(3)生长季呼吸(R-e)和净生态系统交换(N-ee)分别约为实际G的74%和26%。净同化从4月中旬开始，9月初结束。最大的吸收发生在6月，然后是7月和8月。在9月下旬和10月，由于气温较高和森林中大多数树木的落叶，出现了较大的二氧化碳净损失。(4)从2002年8月开始的12个月期间，该森林的碳汇为169-187g Cm(-2)Yr(-1)。应用u*校正后，年碳吸收平均减少24.6g Cm(-2)，相当于校正后的年N-ee值的13.5%。即使在地形较理想的地点，利用涡动协方差确定长期净碳交换的绝对值也存在许多不确定性。未来还需要更详细的实验和相关的理论研究。(C)2006爱思唯尔B.V.保留所有权利。
Eddy-covariance measurements of carbon dioxide exchange were made above a temperate mixed forest for 16 months in northeastern China. The stand is a natural grown, unmanaged mixture of deciduous broad-leaved and coniferous forest and the trees cover a wide range of age classes with a maximum about 450 years. The objective of this study was to test the traditional hypothesis that forests at a late stage of development are insignificant carbon sinks. CO2 exchanges of the ecosystem were studied under conditions of adequate soil water supply. The main results are that:(1) Ecosystem respiration and its components, including soil, stem and leaf respiration, all fit exponential correlations with soil or air temperature, but the ratios of these components to total ecosystem respiration varied during the year. When temperature rose, the ratio of soil respiration to total respiration was relatively stable, while that of leaf and stem respiration increased and decreased, respectively. Soil respiration was the biggest component (48% of the whole ecosystem respiration on average, without including the respiration of fallen trees and coarse woody debris). Leaf respiration was the second largest (22-40%) and stem respiration was the least (13-29%).(2) The ecosystem has very large assimilation potential as environmental factors are adequate in growing season, but the actual gross ecosystem exchange (G(ee)) was only about 45% of the potential due to the influence of water vapor pressure deficit (VPD). High VPD reduced the photosynthetic capacity and the highest relative reductions occurred in afternoon when VPD was higher, with relative reductions between 0.3 and 0.6 during this time. Bigger reduction occurred in May and July, corresponding the 2 months when VPD are higher.(3) Respiration (R-e) and net ecosystem exchange (N-ee) were about 74% and 26% of actual G, during growing season. Net assimilation began in the middle of April and ended in early September. The largest uptake occurred in June, then July and August. Large net CO2 losses occurred in late September and October because of relatively high temperature and leaf fall from most trees in the forest.(4) This forest was a carbon sink of 169-187 g C m(-2) yr(-1) over a 12-month-period commencing August 2002. Application of the u* correction decreased the annual uptake of carbon by 24.6 g C m(-2) on average, corresponding to 13.5% of the corrected annual N-ee.There are many uncertainties for determination of absolute values of long-term net carbon exchange even in sites with ideal topography using Eddy-covariance. More detailed experiments and related theoretical studies are needed in the future. (c) 2006 Elsevier B.V. All rights reserved.