Development of a measurement system of whole-tree gas-exchange

开发了一套测量co_2和H_2O全树气体交换的现场系统。将该系统测量的一棵6.2 m高的白木（Chamaecyparis obtusa）树的叶面积蒸腾速率与用孔隙计测量的蒸腾速率进行了比较，结果表明该系统在精度和响应上与孔隙计几乎相同。利用该系统对一个20年树龄的白木林分的5棵样树进行了1年的光合作用和蒸腾作用测定。光合作用与蒸腾作用密切相关，即光合作用随蒸腾作用的增加而增加。水分利用效率在树木生理活性较高的3 ~ 8月较低，其他月份较高。水分利用效率不仅在月份上存在差异，而且在不同树种间也存在差异。树木的蒸腾速率与树冠底部的茎周平方有明显的大小依赖性，而茎周平方与树木的叶面积密切相关。这种关系由幂函数近似表示。

A field-system for measuring the whole-tree gas-exchange of CO_2and H_2O was developed. We compared transpiration rates on a leaf area basis of a hinoki (Chamaecyparis obtusa) tree 6.2 m high measured with the system to those measured with a porometer, so that it is concluded that the system is nearly the same as the porometer both in accuracy and response.Photocynthesis and transpiration were measured on five sample trees in a 20-year-old hinoki stand over one year using the system. Photosynthesis and transpiration were closely related to each other, i.e., photosynthesis increased with increasing transpiration. Water use efficiency was low in March to August when physiological activity of trees was high, whereas high in other months. The water use efficiency was different not only months, but also among sample trees. There existed a clear size-dependence of the transpiration rate of a tree to the square of stem girth at the bottom of the crown, which is in turn closely related to the foliage area of the tree. The relationship was approximated by the power function.