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刘佳,同小娟,张劲松,孟平,李俊,郑宁.太阳辐射对黄河小浪底人工混交林净生态系统碳交换的影响.生态学报,2014,34(8):2118~2127 本文二维码信息
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太阳辐射对黄河小浪底人工混交林净生态系统碳交换的影响
Impacts of solar radiation on net ecosystem carbon exchange in a mixed plantation in the Xiaolangdi Area
投稿时间:2013-08-18  修订日期:2014-03-20
DOI: 10.5846/stxb201308182105
关键词晴空指数  散射辐射  净碳交换  光合有效辐射  人工混交林
Key Wordsclearness index  diffuse radiation  photosynthetically active radiation  net ecosystem exchange  mixed plantation
基金项目国家自然科学基金(31100322);国家林业局公益性行业项目(GYHY20110400904);北京林业大学科技创新计划项目(YX2011-19)
作者单位E-mail
刘佳 北京林业大学林学院, 北京 100083  
同小娟 北京林业大学林学院, 北京 100083 tongxjsxbs@sina.com 
张劲松 中国林业科学研究院林业研究所 国家林业局林木培育重点实验室, 北京 100091  
孟平 中国林业科学研究院林业研究所 国家林业局林木培育重点实验室, 北京 100091  
李俊 中国科学院地理科学与资源研究所陆地水循环及地表过程重点实验室, 北京 100101  
郑宁 中国林业科学研究院林业研究所 国家林业局林木培育重点实验室, 北京 100091  
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摘要:
太阳辐射是影响森林生态系统与大气间净碳交换(NEE)的主要环境因子之一。利用涡度相关系统和微气象梯度观测系统对黄河小浪底人工混交林CO2通量和相关气象因子进行了3a(2006-2008年)的连续观测;以晴空指数(kt)为指标,分析了2006-2008年生长旺季(6-8月)太阳辐射对该生态系统NEE的影响,讨论了太阳辐射和其他环境因子协同变化对NEE的影响机制。结果表明:2006-2008年生长季,在多云天气下,生态系统最大光合速率Pmax比晴朗天气下分别提高了38%、58%和55%;多云天气下的初始光能利用率α分别是晴天天气的2.6、1.9和2.2倍。晴空指数kt约为0.44的中等辐射条件下,即天空存在一定的云量时,人工混交林生态系统的净碳吸收最大。多云天气下,散射辐射的增加与气象因素变化(气温下降、饱和差减小)的相互作用会增加冠层光合、削弱呼吸作用,从而共同影响了净生态碳吸收的增强。因此,在植被生长旺季,与晴朗无云天气相比,有云层覆盖的天气条件会使人工混交林生态系统的碳吸收能力有所提高。
Abstract:
Light quantity and quality strongly influence plant growth. Solar radiation is one of the main environmental factors driving vegetation carbon assimilation. As one of the natural climatic variables, clouds change the fraction of diffuse radiation arriving on the land surface and can influence carbon dioxide exchange between vegetation and the atmosphere. In this study, CO2 flux was continuously measured during the vegetative growing season (June-August) from 2006 to 2008 by the eddy covariance systems in a mixed plantation in the Xiaolangdi area, Henan province. The clearness index (kt) was used to describe the effects of cloudiness on solar radiation. Clear mornings and afternoons were identified based on the change of kt with solar elevation (β) at a half-day scale. The impacts of cloudiness on the net ecosystem exchange of carbon dioxide (NEE) were investigated to reveal the mechanism of changes in coordinate of solar radiation and other environmental factors on the net carbon uptake by the mixed plantation. The results showed that net CO2 uptake was higher under cloudy skies than that under clear skies. Under cloudy sky conditions, light-saturated maximum photosynthetic rate (Pmax) increased by 38%, 58% and 55% and ecosystem apparent quantum yield (α) increased by factors of 2.6, 1.9 and 2.2 for the mid-growing seasons in 2006, 2007 and 2008, respectively, when compared to clear sky conditions. This work indicates that net carbon exchange could improve in the mixed plantation under cloudy skies relative to clear skies. For a given solar elevation angle interval, when the sky conditions changed from clear to cloudy, total solar radiation received by the ecosystem decreased, and balance of diffuse and direct components of solar radiation received by the ecosystem changed as well. Correspondingly, other environmental factors (Ta, VPD, etc.) also changed. Those changes can influence carbon exchange between forest ecosystem and the atmosphere. During cloudy days, the increase in diffuse radiation received by the ecosystem was more easily absorbed by shaded leaves for photosynthesis in forest canopy with higher leaf area index. Photosynthetically active radiation (PAR) and vapor pressure deficit (VPD) were enhanced with the increase of kt, but diffuse PAR first increased then decreased with the increase of kt. Under cloudy sky conditions, the light distribution is more even and the diffuse radiation received by the forest ecosystem is greater, which benefits photosynthesis of the shaded leaves. VPD is an important factor that affects stomatal conductance. Therefore, the decrease in VPD associated with cloudy conditions can enhance canopy photosynthesis. Temperature is one of the main environmental factors controlling ecosystem respiration. Air temperature declined with the reduction of kt.Net CO2 uptake reached its maximum when kt ranged between 0.4 and 0.5 (the average value was 0.44). When the value of kt was more than 0.5, net CO2 uptake decreased. It is suggested that the increased diffuse PAR, decreased VPD and decreased air temperature under cloudy skies may improve ecosystem photosynthesis and reduce ecosystem respiration, leading to an increase in net carbon uptake in the mixed plantation ecosystem.
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