Ecophysiological Adaptations of the Lichen Genera Pseudocyphellaria and Sticta to South Temperate Rainforests

Abstract

Temperate rainforests are a poorly researched habitat with respect to lichen ecophysiology in comparison to desert and polar regions. The evergreen, broadleaf forests provide a dim, moist environment that is relatively stable throughout the year. Lichens are abundant in both quantity and species diversity with the large foliose genera Sticta and Pseudocyphellaria normally being dominant, visually and in terms of biomass. These lichens exhibit a great diversity of both form and habitat range. Physiological and morphological adaptation has also been demonstrated. Pseudocyphellaria dissimilis shows changes in thallus water storage capacity with evaporative demand and is also highly shade-adapted. The species has the lowest light saturation and compensation values for photosynthesis yet known for lichens (20 and 1-μmol m⁻²s⁻¹, PAR, respectively). Unexpectedly it is also highly desiccation-sensitive with some thalli being killed after only 20 h exposure to 15% relative humidity. Photobiont versatility is also a feature of these genera. Photosymbiodemes occur, i.e. a single thallus containing both green algal and cyanobacterial sectors. Because the different sectors have the same fungal partner and grow in the same habitat, it is possible to investigate whether particular physiological traits are photobiont determined. The ability to recover photosynthetic activity in humid air is confined to thalli with green algal photobionts whilst the inability of thalli containing cyanobacterial photobionts to tolerate high light stress may be related to their lack of a protective xanthophyll cycle.