不同土壤水分下侧柏苗木光合特性和水分利用效率的研究

在黄土半干旱区,采用人工控制土壤水分的方法,使用Li-6400便携式光合作用测定系统,对侧柏苗木净光合速率、蒸腾速率、气孔导度、胞间CO2浓度及其相应的环境因子进行了测定。结果表明:不同土壤水分状况下侧柏苗木光合速率日变化曲线呈“双峰”型,均有不同程度的“午休”现象,且上午的光合速率明显高于下午;气孔导度受水分和光热胁迫的影响,日变化曲线呈凹型;胞间CO2浓度受空气CO2浓度和气孔导度的双重影响,呈现出早晚高,正午低的日变化进程;水分利用效最高值出现在上午较早的时分,且上午的水分利用效率明显高于下午;随着土壤水分的增加,净光合速率和蒸腾速率升高,而水分利用效率降低。根据Farquhar和Sharkey的观点,造成净光合速率下降的原因既有气孔限制又有非气孔限制因素,上午净光合速率下降的主要是由气孔限制因素造成的,午间和下午光合速率的降低则主要归因于叶肉细胞羧化效率的降低。

Characteristics of Photosynthesis and Water Use Efficiency of Platycladus orientalis Under Different Soil Moisture

In semi-arid region of Loess Plateau,the net photosynthetic rate,transpiration rate,stomatal conductance,intercellular CO_2 concentration of Platycladus orientalis and proportional factors were measured with the Li-6400 portable photosynthesis system under the condition of controlled soil moisture.The results showed that the diurnal course of net photosynthetic rate displayed a two-peak pattern and a typical midday depression pattern,net photosynthetic rate in forenoon was higher than that in afternoon;stomatal conductance was affected by the water,light and heat stress,which displayed a hollow pattern;intercellular CO_2 concentration was affected by the atmosphere CO_2 concentration and stomatal conductance,which displayed a hollow pattern;water use efficiency culminated in the early morning,water use efficiency in forenoon was higher than that in afternoon;the net photosynthetic rate and transpiration rate increased with an increase of the soil moisture,while water use efficiency declined.On the basis of two criteria of stomatal limitation of photosynthesis suggested by Farquhar and Sharkey,the re-dominant limiting factor of photosynthesis is stomatal conductance of stomatal limitation in the forenoon,but the midday depression of photosynthesis at noon and the decrease of photosynthesis in the afternoon are the results of low carboxylation efficiency of the mesophyll leaf.