植物群体结构与太阳辐射的垂直分布及其变化

茶树、小麦和樟树群体叶面积垂直分布的差异显著，但在一定精度内，它们可用相同的函数形式描述，具有理论意义。茶树叶倾角基本服从正态分布，方差较大。不同的植物群体中，太阳辐射的垂直分布有别，与群体叶面积垂直分布密切相关。光合有效辐射（PAR）的消光系数大于总辐射（TSR）的消光系数；一天中，群体下部的光照条件以中午前后为佳，消光系数（k）最小；k值与太阳高度角的正弦成反比。考虑到k值的日变化，指数衰减律仍不失为一种简单实用的数学模型。

Canopy Structures and Radiation Regimes and Their Variations

A mathematical model was introduced to describe the vertical distribution of leaf area densities of tea, wheat, and cinnamon canopies and it fitted the data very well although their patterns are considerably different. Therefore, this model is theoretically significant. Leaf declination angles of tea, with a great covariance, tend to be a normal distribution. Radiation regimes vary notably in different canopies; however, light conditions in the lower part of the canopies are the best around noon when extinct coefficient is the smallest. The extinct coefficients being greater for photosynthetically active radiation (PAR) than those for total radiation (TSR) are closely related to the inverse proportion of solar altitudes (sinh0) during one day. Consequantly, under rational consideration of daily variation of the extinct coefficients, traditional exponentially extinguishing relationship is still a good mathematical model for describing radiation regimes within plant canopies with the advantages of being simple, practical, and trustworthy.