GEOGRAPHICAL RESEARCH ›› 2009, Vol. 28 ›› Issue (6): 1673-1681.doi: 10.11821/yj2009060023

• Environment and Ecology • Previous Articles     Next Articles

Influence of diffuse radiation on the net CO2 exchange of alpine meadow ecosystem on Tibet Plateau

FAN Yu-zhi, ZHANG Xian-zhou, SHI Pei-li   

  1. Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China
  • Received:2009-04-03 Revised:2009-08-26 Online:2009-11-25 Published:2009-11-25
  • Supported by:

    国家重点基础研究发展计划 ( 2005CB422005 ) ;中国科学院知识创新工程重要方向 ( KSCX2-YW-N-44 ) 。

Abstract:

The net CO2exchange between the atmosphere and alpine meadow ecosystem (NEE) and standard meteorological parameters were measured by Eddy covariance technique in Damxung County, Tibet from 2004 to 2006. Based on the data, net CO2exchange response characteristic of alpine meadow ecosystem on Tibet Plateau to diffuse radiation was analyzed. The ground conditions can be separated into three types: cloud-gap sky condition, clear-sky condition and overcast-sky condition by the clearness index as a criterion. Although in cloud-gap and overcast situations the diffuse radiation can be enhanced, the ground surface under a cloud-gap sky receives the same amount of direct beam radiation as under a clear sky, while under overcast sky, the direct beam radiation is reduced. We compared the enhanced NEE from three sky conditions for 5° interval of solar elevation angles and 5℃ interval of soil temperature. The results show that the scatterplots between the net ecosystem CO2 exchange and clear index present a different pattern in three ground conditions. It is shown that, no matter whether the site is under a clear sky, a cloud-gap sky or an overcast sky, the carbon uptake does not tend to be enhanced. That is to say, the trend of change on the net ecosystem CO2 exchange with the clear index was not affected by diffuse radiation, but affected by coupling effect of the solar radiation intensity and the soil temperature. During the daytime, photosynthetically active radiation dominated the carbon absorption, and soil temperature dominated the carbon emission. Generally speaking, the maximal NEE occurs under three skies with the soil temperature at 15℃, and the clearness index between 0.7 and 0.8.

Key words: alpine meadow ecosystem, diffuse radiation, the Tibet Plateau, net ecosystem CO2 exchange