Evaluation of CO2-fixation capacity in Sugi (Cryptomeria japonica) canopy

为了揭示柳杉冠层固碳能力，对决定叶片分布的树枝结构和决定叶片生产力的树冠内叶片氮素分布进行了研究。(1)树枝结构遗传测定了树冠内的树枝密度和树枝分布，这些树枝特征可作为树冠结构模型的参数。树冠中上部的树枝具有空间扩展功能，下部树枝具有空间填充功能。树冠厚度对树冠形状没有影响，但叶质量及其分布发生了变化。结果表明，间伐通过改变叶片质量和叶位来影响叶片生产力，修剪后茎、枝的生长均有所下降。枝条生长的下降率小于枝条的下降率，树冠形状向伞形转变。这一现象可以解释为叶片为补偿光合器官损失而发生的重排。(2)叶片氮素分配：当年叶的氮素含量随着光照强度的降低而降低，然后是冠层上部含氮量较高，冠层下部含氮量较低。老叶含氮量低且稳定，研究了不同生长部位对叶片含氮量的影响。树冠含氮量受光照强度和立地指数两个参数控制。这两个参数可以作为影响冠层叶片含氮量的主要因素。利用叶片氮素分布和叶片光合作用参数，建立了杉木冠层固碳能力的估算模型。将该模型应用于某杉木林分，计算结果能较好地解释林分数据。

To reveal the CO2-fixation capacity of Sugi (Cryptomeria japonica D.Don) canopy, (1) branch structure which determine the leaf distribution, (2) leaf nitrogen distributin in a crown which determine the leaf productivity were investiqated.(1) branch structureBranch density and branch distribution in an individual sugi crown were determined hereditarily, and these branch characteristics can be used as parameters of crown structure model.The branches attached at the upper and middle parts of a crown had the space spreading function and the lower branches had the spcace filling function.Thinning had not affected the crown shape, but leaf mass and their distribution had changed. We concluded that thinning has an effect on leaf productivity by changing leaf mass and their position.The growth of stem and branch had decreased after pruning. The decreasing rate of branch growth was smaller than that of shoot, then the crown shape had changed to an umbrella type. This phenomena can be explained as a rearrangement of leaves for the compensation of photosynthetic organ loss.(2) Leaf nitrogen distributionNitrogen content of a current year leaves decreased according to light intensity decrease, then nitrogen content of upper crown was high and that of lower crown was low. Nitrogen content of old leaves was low and constant.The effect of growing site on leaf nitrogen content was investigated. Leaf nitrogen content in a crown was under the control of two parameters, namely, light intensity and site index. These two parameters can be used as main factors affecting leaf nitrogen content in a crown.A model for estimating CO2-fixation of a Sugi canopy was constructed using leaf nitorogen distribution and leaf photosynthesis parameters. This model was applied to a some sugi stand and the calculation result was sufficiant for explaining the stand's data.