中文摘要：

在2007年7—8月棉花生长旺季,将冠层按高度分多层,通过简单的试验方法确定了棉冠内叶片丛聚指数（clumping index,Ω）,以此区分计算出田间各层逐时阳叶（受光叶）和阴叶（被遮荫叶）叶面积指数的动态值。在8月23日用LI-6400R便携式光合测量系统分多层分别测定阴、阳叶单张叶片净光合作用的日变化,结合阴、阳叶面积权重,探讨利用Ω区分阴阳叶之后对整个冠层日总光合作用的影响。试验结果表明：（1）花铃期棉花冠层内Ω约为0.68;（2）利用Ω计算得到8月23日冠层日间（09：00—18：00）总净光合作用日平均值大约为20.3μmol·m-2·s-1,其中阳叶贡献约占总量的72%,阴叶约占总量的28%;（3）上层叶片贡献约占总量的75%,中层叶片约占总量的22%,下层叶片约占总量的3%。

英文摘要：

Experimental studies for photosynthesis were conducted at Yucheng Comprehensive Experimental Station of the Chinese Academy of Sciences from July to August in 2007.In the frame of a two-leaf-multilayer model,daily variation of leaf level net photosynthesis rate in a cotton field was studied by using a LI-6400R portable photosynthesis system during this period.A foliage clumping index（Ω） was used to calculate the sunlit and shaded leaf area index（LAI） after stratification,and the contributions of their photosynthesis to total dry matter formation were calculated separately.Based on these observations,daily gross photosynthesis from leaf to canopy can be estimated.In this experiment,the clumping index was confirmed to be about 0.68,the mean daily gross photosynthesis on August 23（from 09：00 to 18：00 BST） was 20.3 μmol·m-2·s-1;the sunlit leaf’s photosynthesis was about 72% of the total and that of the shaded leaf was about 28%.The photosynthesis in the top layer was about 75% of the total,indicating that the canopy photosynthesis depends mostly on leaves of the top layer.