Lange O L, Green T G A, Ziegler H
Lehrstuhl für Botanik II der Universität Würzburg, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Federal Republic of Germany.
Biological Sciences, Waikato University, Hamilton, New Zealand.
Oecologia. 1988 May;75(4):494-501. doi: 10.1007/BF00776410.
Green lichens have been shown to attain positive net photosynthesis in the presence of water vapour while blue-green lichens require liquid water (Lange et al. 1986). This behaviour is confirmed not only for species with differing photobionts in the genusPseudocyphellaria but for green and blue-green photobionts in a single joined thallus (photosymbiodeme), with a single mycobiont, and also when adjacent as co-primary photobionts. The different response is therefore a property of the photobiont. The results are consistent with published photosynthesis/water content response curves. The minimum thallus water content for positive net photosynthesis appears to be much lower in green lichens (15% to 30%, related to dry weight) compared to blue-greens (85% to 100%). Since both types of lichen rehydrate to about 50% water content by water vapour uptake only green lichens will show positive net photosynthesis. It is proposed that the presence of sugar alcohols in green algae allow them to retain a liquid pool (concentrated solution) in their chloroplasts at low water potentials and even to reform it by water vapour uptake after being dried. The previously shown difference in δC values between blue-green and green lichens is also retained in a photosymbiodeme and must be photobiont determined. The wide range of δC values in lichens can be explained by a C carboxylation system and the various effects of different limiting processes for photosynthetic CO fixation. If carboxylation is rate limiting, there will be a strong discrimination ofCO, at high internal CO partial pressure. The resulting very low δC values (-31 to-35‰) have been found only in green lichens which are able to photosynthesize at low thallus water content by equilibraiton with water vapour. When the liquid phase diffusion of CO becomes more and more rate limiting and the internal CO pressure decreases, theC content of the photosynthates increases and less negative δC values results, as are found for blue-green lichens.
已表明，绿藻地衣在有水蒸气存在时可实现净光合作用为正，而蓝藻地衣则需要液态水（兰格等人，1986年）。不仅对于假杯点衣属中具有不同光合生物的物种，而且对于单个联合叶状体（光合共生体）中具有单个真菌共生体的绿藻和蓝藻光合生物，以及当它们作为共同初级光合生物相邻时，这种行为都得到了证实。因此，不同的反应是光合生物的一个特性。这些结果与已发表的光合作用/水分含量响应曲线一致。与蓝藻地衣（85%至100%，相对于干重）相比，绿藻地衣中净光合作用为正的最低叶状体水分含量似乎要低得多（15%至30%）。由于两种地衣仅通过吸收水蒸气就可再水化至约50%的水分含量，所以只有绿藻地衣会表现出净光合作用为正。有人提出，绿藻中糖醇的存在使它们能够在低水势下在叶绿体中保留一个液池（浓缩溶液），甚至在干燥后通过吸收水蒸气重新形成液池。先前显示的蓝藻地衣和绿藻地衣之间δC值的差异在光合共生体中也得以保留，并且一定是由光合生物决定的。地衣中δC值的广泛范围可以用C羧化系统以及光合固定CO₂的不同限制过程的各种影响来解释。如果羧化是限速的，在高内部CO₂分压下对CO₂会有强烈的分馏作用。仅在能够通过与水蒸气平衡在低叶状体水分含量下进行光合作用的绿藻地衣中发现了由此产生的非常低的δC值（-31至-35‰）。当CO₂的液相扩散越来越成为限速因素且内部CO₂压力降低时，光合产物的C含量增加，δC值变得不那么负，这与蓝藻地衣的情况相同。
