Lange Otto L, Green T G Allan
Lehrstuhl für Botanik II, Julius-von-Sachs-Institut für Biowissenschaften der Universität Würzburg, Mittlerer Dallenbergwèg 64, D-97082, Würzburg, Germany.
Department of Biological Sciences, The University of Waikato, Private Bag 3105, Hamilton, New Zealand.
Oecologia. 1996 Oct;108(1):13-20. doi: 10.1007/BF00333209.
Experiments under controlled conditions have shown that net photosynthesis (NP) of many lichens is depressed when their thalli are highly hydrated. In this study we characterise the light and water content (WC) dependency of CO exchange for selected epilithic lichens in the laboratory and match this against samples monitored in their natural habitat by a novel, fully automatic cuvette. Laboratory measurements showed that, at a photosynthetic photon flux density (PPFD) of 1500 μmol m s, NP of the epilithic foliose lichen Xanthoria calcicola was reduced by about 85% (compared to NP at optimal water content) when the thallus was suprasaturated (maximal hydration was defined as WC after spraying, submerging and subsequent removal of adhering water droplets by shaking). Only after loss of about 80% of its maximal WC were the highest rates of NP possible. This depression was still substantial at 50 μmol m s PPFD. Responses were similar for the crustose epilithic species Lecanora muralis. CO exchange of both lichens was monitored under natural conditions by means of the cuvette built into a man-made wall-a common habitat of the species-in the Botanical Garden, Würzburg. For both species, rates of NP were low during and after heavy rain even if incident PPFD and temperature were favourable. This situation occurred frequently and could last through all daylight hours, resulting in a negative carbon balance when nocturnal rates of respiration were high. Often, after rainfall, there was a brief, high peak of NP when optimal WC was transiently attained before metabolic activity finally ceased through desiccation. Other periods with profitable rates of NP occurred after moderate moistening of the lichens by dew, fog or light rain. The lichens were found to perform identically in the field and laboratory. When the two data sets were compared it was clear that the full range of WC produced in the laboratory also occurred in nature and that the productivity of the epilithic lichens was regularly and severely limited by high WC. It is concluded that blockage of diffusive pathways for CO in the thallus through high water contents is an important ecological factor for productivity of these central European epilithic lichens.
在可控条件下进行的实验表明，当许多地衣的叶状体高度水合时，其净光合作用（NP）会受到抑制。在本研究中，我们在实验室中对选定的石生附生地衣的CO交换的光和含水量（WC）依赖性进行了表征，并通过一种新型的全自动比色皿将其与在自然栖息地监测的样本进行匹配。实验室测量表明，在光合光子通量密度（PPFD）为1500 μmol m² s⁻¹时，当叶状体处于过饱和状态（最大水合定义为喷雾、浸没并通过摇晃去除附着的水滴后的WC）时，石生叶状地衣石黄衣（Xanthoria calcicola）的NP降低了约85%（与最佳含水量下的NP相比）。只有在损失约80%的最大WC后，才可能达到最高的NP速率。在PPFD为50 μmol m² s⁻¹时，这种抑制仍然很显著。壳状石生种类墙茶渍衣（Lecanora muralis）的响应类似。通过安装在维尔茨堡植物园人工墙壁（该物种的常见栖息地）中的比色皿，在自然条件下监测了这两种地衣的CO交换。对于这两个物种，即使入射PPFD和温度适宜，大雨期间和之后NP速率也很低。这种情况经常发生，可能持续整个白天，当夜间呼吸速率较高时，会导致负碳平衡。通常，降雨后，当短暂达到最佳WC，然后代谢活动最终因干燥而停止之前，会出现短暂的NP高峰。在露水、雾气或小雨使地衣适度湿润后，还会出现其他NP速率有利的时期。发现地衣在野外和实验室中的表现相同。当比较这两组数据时，很明显实验室中产生的整个WC范围在自然界中也会出现，并且石生附生地衣的生产力经常受到高WC的严重限制。结论是，叶状体中高含水量导致的CO扩散途径受阻是这些中欧石生附生地衣生产力的一个重要生态因素。
