不同季节中香荚兰叶片的光合作用特征

PHOTOSYNTHETIC PROPERTIES OF LEAVES IN VANILLA PLANIFOLIA AMONG DIFFERENT SEASONS

通过对生长于人工阴蔽下香荚兰(Vanilla planifolia)不同部位叶片的气体交换、可滴定酸度和叶绿素含量等四个不同季节的观测,较为详细地研究了叶龄和光合作用类型之间的关系及其季节性的变化规律。成熟叶片在四个季节中表现为稳定的景天酸代谢(CAM),且光期有较长时间的CO_2吸收,几乎无CO_2向外释放,有显著的昼夜酸度波动。幼叶以C_3代谢为主,但在较高昼夜温差和较低空气相对湿度的条件下也能进行CAM代谢,且不同季节中表现了不同程度的酸积累。我们认为,香荚兰叶片随叶龄的增长有一个从C_3代谢到CAM代谢的光合作用途径的转移,幼叶在对环境因子变动的反应中也有一个类似的转移现象。叶片的光合作用能力也表现了季节性的差异,尤其对温度反应敏感,低温季节(日均温<20℃),CO_2的固定作用大大减弱。

Leaf gas exchange, titratablc acidity and chlorophyll content were measured in Vanilla planifolia cultivated in artificial shading condition during four different seasons. The relationship between different leaf ages and photosynthetic types and seasonal variations were researched in detail. The mature leaves perform stable Crassulacean Acid Metabolism (CAM), which uptake and rarely release CO2 for most times during the light period, and express marked diurnal acid fluctuation. The young leaves mainly carry on C3-mctbolism under the conditions of higher diurnal temperature diffences and lower air relative humidity, and express nocturnal acid accumulation for different levels among different seasons. We consider that the photosynlhetic carbon metabolism ways of leaves in Vanilla planifolia shifts from C3 to CAM along with leaf development. The young leaves also shift similarly in response to environmental perturbations. Leaf photosynthetic capacity shows seasonal variation, especially sensitive to temperature. CO2 fixation is weakened greatly during the low temperature season Cr<20℃).