Fungal melanins as a sun screen for symbiotic green algae in the lichen Lobaria pulmonaria

  • Gauslaa Y
  • Solhaug K
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Abstract

The mycobiont of the high-light-susceptible forest lichen Lobaria pulmonaria was shown to deposit brown, melanic compounds in the outer layer of the up- per cortex, depending on the long-term level of solar ra- diation 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 re- ducing 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 photo- bionts of melanic L. pulmonaria thalli are relatively sus- ceptible to high-light exposure. Since melanins also in- crease the absorbance of solar energy for the whole thal- lus, 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

Author-supplied keywords

  • Cortical transmittance
  • Lichen symbiosis
  • Photoprotection
  • Spectral characteristics
  • UVB

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