Gauslaa Yngvar, Solhaug Knut Asbjørn
Department of Biology and Nature Conservation, The Agricultural University of Norway, P.O. Box 5014, 1432, Ås, Norway.
Oecologia. 2001 Feb;126(4):462-471. doi: 10.1007/s004420000541. Epub 2001 Feb 1.
The mycobiont of the high-light-susceptible forest lichen Lobaria pulmonaria was shown to deposit brown, melanic compounds in the outer layer of the upper cortex, depending on the long-term level of solar radiation in its natural habitat. Furthermore, pale thalli from a shady habitat produced melanic compounds after transplantation to a sunny habitat. This browning of the cortex appeared to be a physiologically active process, taking place only during periods with frequent hydration. Melanin production was slow. After transplantation, more than 1 year was needed for a shade-adapted thallus to reduce the cortical transmittance (230-1000 nm) to a similar level to that of naturally sun-exposed specimens. Melanic compounds acted as a sun screen, especially reducing UVB and UVA wavelengths, but also visible wavelengths, at the photobiont level. In the near infrared range, there was only a small difference in transmittance between shade- and sun-adapted cortices. A negative correlation was found between the natural light level and the cortical transmittance of wavelengths below 700 nm. However, previous studies have shown that even photobionts of melanic L. pulmonaria thalli are relatively susceptible to high-light exposure. Since melanins also increase the absorbance of solar energy for the whole thallus, it appears that what is gained in terms of UV- and light protection in melanic L. pulmonaria specimens may be offset by increased exposure to excess temperatures for this highly heat-susceptible lichen.
研究表明，高光敏感型森林地衣肺衣的菌髓在其上部皮层外层沉积棕色的黑色素化合物，这取决于其自然栖息地的长期太阳辐射水平。此外，来自阴凉栖息地的浅色叶状体在移植到阳光充足的栖息地后会产生黑色素化合物。皮层的这种褐变似乎是一个生理活跃过程，仅在频繁补水期间发生。黑色素生成缓慢。移植后，适应阴凉环境的叶状体需要1年多的时间才能将皮层透光率（230 - 1000纳米）降低到与自然暴露在阳光下的标本相似的水平。黑色素化合物起到了防晒作用，特别是在共生光合生物层面减少了UVB和UVA波长，也减少了可见光波长。在近红外范围内，适应阴凉和阳光环境的皮层之间的透光率只有很小的差异。发现自然光水平与700纳米以下波长的皮层透光率之间呈负相关。然而，先前的研究表明，即使是黑色素化的肺衣叶状体的共生光合生物也相对容易受到高光照射。由于黑色素也会增加整个叶状体对太阳能的吸收，对于这种对高温高度敏感的地衣来说，黑色素化的肺衣标本在紫外线和光保护方面获得的益处似乎可能会被过度暴露于高温所抵消。
