Ecology and physiology of the Antarctic fruticose lichen Usnea sulphurea (Koenig) Th. Fries

Summary

Only a few small areas of the coast of north Victoria Land are free of ice. Such an area is Birthday Ridge, Yule Bay, where a lichen vegetation is developed in the interspaces of granitic rocks of the mountaintop detritus. The largest and most frequent lichen is Usnea sulphurea, growing as a “light” form at exposed habitats and as a “shade” form below pebbles. Both forms differ by chlorophyll content and temperature dependency of net photosynthesis, which demonstrates an adaptive response of these forms to their environment. Usnea sulphurea is able to take up water from humid air, but in its natural habitat it is moistened mostly by melting snow. CO₂-gas exchange is detectable when the water content of the thalli rises above 30% of the dry weight. A decrease of net photosynthesis at very high water contents (at 6°C) is not visible. At a CO₂ concentration of the air below 200 ppm the lichens have a negative CO₂ balance; net photosynthesis is still not saturated at 370 ppm CO₂ in the air under the experimental conditions. Like other antarctic lichens, U. sulphurea is a moderately productive, slowly growing species.