Lange O L, Tenhunen J D
Lehrstuhl für Botanik II, Universität Würzburg, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Germany.
Oecologia. 1981 Jan;51(3):426-429. doi: 10.1007/BF00540917.
Thalli of Ramalina maciformis were moistened to their maximal water holding capacity, thus, simulating actual conditions following a heavy rainfall. Time courses of net photosynthesis at 17° C and 750 μE m s light intensity (PAR) were obtained during drying of the thalli. At ambient CO concentrations from 200 to 1,000 ppm, CO uptake of the moist lichens was depressed at high water content. After a certain water loss, net photosynthesis increased to a maximal value and decreased again with further drying of the thalli. The degree of initial depression of photosynthesis decreased with increasing ambient CO concentration, and it was fully absent at 1,600 ppm ambient CO. Under these conditions of CO saturation, net photosynthesis remained constant at maximum for many hours and decreased only when substantial amounts of water had been lost. We conclude that the carboxylation capacity of the lichen is not affected by high contents of liquid water. Therefore, the depression of CO uptake of the water saturated lichen at lower (e.g. natural) ambient CO must be due exclusively to increased resistance to CO diffusion from the external air to the sites of carboxylation.
将大型石蕊地衣的叶状体湿润至其最大持水量，从而模拟暴雨后的实际情况。在叶状体干燥过程中，获得了17℃和750μE m⁻² s⁻¹光强（光合有效辐射）下的净光合作用时间进程。在200至1000 ppm的环境CO₂浓度下，含水量高时，湿润地衣对CO₂的吸收受到抑制。经过一定程度的水分流失后，净光合作用增加到最大值，随着叶状体进一步干燥又再次下降。光合作用初始抑制程度随环境CO₂浓度升高而降低，在1600 ppm环境CO₂时完全不存在这种抑制。在这些CO₂饱和条件下，净光合作用在数小时内保持最大值不变，仅在大量水分流失时才下降。我们得出结论，地衣的羧化能力不受液态水高含量的影响。因此，在较低（如自然）环境CO₂浓度下，水分饱和的地衣对CO₂吸收的抑制必定完全归因于从外部空气到羧化位点的CO₂扩散阻力增加。
