林冠结构、辐射传输与冠层光合作用研究综述

Review on Forest Canopy Structure,Radiation Transfer and Canopy Photosynthesis

林冠内辐射的分布常用泊松分布、二项分布等来描述 ,主要取决于叶片的空间散布状态。冠形与辐射分布和冠层光合作用密切相关 ,影响程度与地理纬度、太阳高度、林分密度等有关。叶片方位角为随机分布通常是合理的假设。叶倾角分布对叶片尺度的辐射吸收和光合作用是十分重要的 ,但在冠层尺度上的影响则小得多 ,并与其它冠层结构因素有关。由于叶倾角的测定十分困难 ,因而球面和椭球面叶倾角分布是常用的假设。不同的树冠分布方式及在单个树冠内叶片成簇或随机分布 ,都会对冠层辐射分布和光合作用产生重要影响。对树冠高大而叶片较小的林冠 ,半影效应可使辐射在叶片上更趋向均匀分布。目前多以圆形叶片作为计算半影效应的基础。尽管叶片的透射、反射和散射只占总辐射的百分之几 。

Canopy structural factors with radiation distribution and canopy photosynthetic modelling inclued crown shape,leaf angle distribution,leaf distribution within canopy,penumbra effect,reflection and scattering of leaf on radiation etc.The radiation within canopy was mainly described with Poisson distribution or binomial distribution,depending on the uniformity of leaf distribution.Crown shape was closely related to radiation transfer and canopy photosynthesis,however,influenced by latitude,sun height and stand density,there were no specific crown shape that was absolutely favorable for canopy photosynthesis.Leaf angle was believed to be important at leaf scale but could be neglected at canopy scale.Spherical and /or elliptical leaf angle distribation were proposed hypothesis in canopy radiation and photosynthetic modelling.Leaf distribution within canopy was one of the most important structural factors affecting radiation transfer and canopy photosynthesis.The uneven canopy surface,clumped,regular and/or random crown distribution,and clustered or random leaf distribution within crown would greatly influence radiation transfer and canopy photosynthetic modelling.Penumbra effect within high canopy with small leaf were believed to be significant,however,since penumbra effect was currently estimated on circular leaf,it is necessary to develop a more practical estimation method particularly for coniferous forest. The reflection and scattering of leaf on radiation are also important factors in radiation transfer and canopy photosynthetic modelling although they account for only several percent of total radiation.