黄土半干旱区侧柏气体交换和水分利用效率日变化研究

利用Li 6 2 0 0便携式气体分析系统 ,对黄土半干旱区山西省方山县试验地自然条件下 ,侧柏的气体交换、气孔导度和水分利用效率及相应环境因子进行测定 .结果表明 ,净光合速率日变化曲线呈双峰型 ,气孔导度日变化曲线呈凹型 ,蒸腾速率日变化曲线呈单峰型 ,水分利用效率最高值出现在上午较早时分 .根据Farquhar和Sharkey提出关于区分光合作用的气孔限制与非气孔限制的两个标准 ,分析表明侧柏在上午 (1 0 :0 0— 1 2 :0 0 )光合速率下降主要是由气孔因素的气孔导度决定的 ,而午间 (1 2 :0 0— 1 4 :0 0 )的光合午休和午后 (1 6 :0 0— 1 8:0 0 )光合速率的下降则主要归因于非气孔因素的叶肉细胞羧化能力的降低 .

Diurnal course of gas exchange and water use efficiency of Platycladus orientalis in a semi-arid region of the Loess Plateau

The daily gas exchange,stomatal conductance and water use efficiency of Platycladus orientalis in the test area of Fangshan Country of Shanxi Province in a semi-arid region of the Loess Plateau were measured with a portable Li --6200 gas analysis system under natural conditions.The results show that the diurnal course of net photosynthetic rate displays a two-peak pattern,that of stomatal conductance a hollow pattern and that of transpiration rate a signal-peak pattern.Water use efficiency culminates in the early morning.On the basis of two criteria of stomatal limitation of photosynthesis suggested by Farquhar and Sharkey,the predominant limiting factor of photosynthesis is stomatal conductance of stomatal limitation in the morning (10:00? ?2:00).The midday depression of photosynthesis at noon(12:00—14:00) and the decrease of photosynthesis in the afternoon (16:00—18:00)are the result of the low carboxylation capacity of the leafmesophyll.