小青杨（populuspseud－simoni）生理生态特性的研究

Study on Physiological Ecological Characteristics of Populus Pseud Simonii

在野外条件下，测定了小青杨树冠不同方向净光合速率和呼吸速率日进程呈双峰曲线形式，双峰出现在上午９时及下午１５时，低谷出现在１３时，即“午睡现象”，这与光照强度关系不大，而与环境因子有密切关系。小青杨树冠四个方向的光照强度都呈单峰曲线形式、温度也呈单峰曲线形式，但二者的峰值不同。树冠不同方向水分状况不同，饱和亏缺大者，水势较小，蒸腾强度也小。树冠不同方向，叶绿素含量不一，东面和北面叶绿含量较其他两面高，ａ／ｂ比值小于１。

This paper concerns with the studies of the diurnal change of the net photosynthetic and respiratory rates of populus pseud-simonii. The results showed the change appeared as a double-peak curve. The peaks appeared at 90′clock in the morning and at 15 o′clock in the afternoon. The lowest appeared at 1 o′clock in the afternoon, in other words, minimum at noon. The diurnal change depended on the environmental factor.