中文摘要：

玉米冠层内光合有效辐射（PAR）的大小直接影响冠层内叶片的光合作用,进而影响玉米净第一性生产力或作物产量的准确评估。为弄清玉米冠层内光合有效辐射的分布规律及其影响因子,基于锦州玉米农田生态系统于2006年生育期的光合有效辐射观测数据和叶面积指数动态观测数据,对玉米冠层光合有效辐射的垂直分布特征及其影响因子进行了分析。结果表明：玉米冠层内不同垂直层次叶片的PAR分布随生育期变化显著,与叶面积指数呈显著的负相关（R2=0.89）;玉米冠层光合有效辐射的消光系数K值在生育期呈动态变化,约为0.76,且表现为苗期较大、生育后期较小。分析表明,在进行光合有效辐射及与此密切相关的光合作用模拟时,应考虑消光系数的动态变化。

英文摘要：

Photosynthetically active radiation （PAR） in plant canopy plays a very important role in leaf photosynthesis. Understanding the distribution characteristics of PAR in the canopy and its controlling factors is essential to evaluate accurately net primary productivity （NPP） of vegetation and crop yield. PAR and leaf area index （LAI） at different heights in the canopy during the growing period of 2006 were measured by LI-6400 photosynthesis measurement system （ Li-cor, Lincoln, NE, USA） and harvest method, respectively. Based on the observation data of PAR and LAI during maize growth period of 2006 in Jinzbou agricultural ecosystem station, the vertical distribution characteristics of PAR in maize canopy and its controlling factors were analyzed. The variations of extinction coefficient （K） were also discussed at the different growth periods according to the light transmission pattern followed by Beer-Lambert law in vegetation canopy. The results show that PAR in different vertical heights of maize canopy changes obviously with the variations of growth periods. There is a negative correlation between PAR and LAI （ R^2 = 0.89）. The extinction coefficient （ K ） is dynamic during different growth periods, and the value is about 0.76. K value is larger in the seedling period,and it is smaller in later growth period. The dynamic K values should be used in order to accurately simulate PAR and relative photosynthesis in the canopy.