Winter K, Schramm M J
Lehrstuhl für Botanik II and Lehrstuhl für Botanik I, Universität Würzburg, Mittlerer Dallenbergweg 64, 8700 Würzburg, West Germany.
Plant Physiol. 1986 Sep;82(1):173-8. doi: 10.1104/pp.82.1.173.
In well-watered plants of Welwitschia mirabilis, grown in the glass-house under high irradiance conditions, net CO(2) assimilation was almost exclusively observed during the daytime. The plants exhibited a very low potential for Crassulacean acid metabolism, which usually resulted in reduced rates of net CO(2) loss for several hours during the night. In leaves exposed to the diurnal changes in temperature and humidity typical of the natural habitats, CO(2) assimilation rates in the light were markedly depressed under conditions resembling those occurring during midday, when leaf temperatures and the leaf-air vapor pressure differences were high (36 degrees C and 50 millibars bar(-1), respectively). Studies on the relationship between CO(2) assimilation rate and intercellular CO(2) partial pressure at various temperatures and humidities showed that this decrease in CO(2) assimilation was largely due to stomatal closure. The increase in the limitation of photosynthesis by CO(2) diffusion, which is associated with the strong decline in stomatal conductance in Welwitschia exposed to midday conditions, may significantly contribute to the higher (13)C content of Welwitschia compared to the majority of C(3) species.
在温室中高光照条件下生长的水分充足的百岁兰植株中，净二氧化碳同化几乎只在白天观察到。这些植株的景天酸代谢潜力非常低，这通常导致夜间数小时内净二氧化碳损失率降低。在暴露于其自然栖息地典型的昼夜温度和湿度变化的叶片中，在类似于中午出现的条件下，即叶片温度和叶-气蒸汽压差较高（分别为36摄氏度和50毫巴bar⁻¹）时，光照下的二氧化碳同化率明显降低。在不同温度和湿度下对二氧化碳同化率与细胞间二氧化碳分压之间关系的研究表明，这种二氧化碳同化的降低主要是由于气孔关闭。与暴露于中午条件下的百岁兰气孔导度大幅下降相关的二氧化碳扩散对光合作用限制的增加，可能显著导致百岁兰与大多数C₃物种相比具有更高的¹³C含量。
