Ecophysiology of Lichens in the Dry Valleys of Southern Victoria Land, Antarctica I. Microclimate of the Cryptoendolithic Lichen Habitat

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Summary The microclimate of the cryptoendolithic lichen habitat was studied on Linnaeus Terrace (1,600–1,650 m alt.) in the mountainous region of the Antarctic dry valleys between Nov. 30 and Dec. 11, 1979. Three types of weather conditions occurred: 1) overcast, with periods of fog and snow, 2a) clear and windy, and 2b) clear with no winds. Air temperature was consistently below −6 °C. Relative humidity rose to 74% on an overcast day, but was lower (16–47%) on clear days. The northern face of sandstone rocks, mostly exposed to the sun, is colonized by lichens, while the southern, shaded face is free of lichens. Temperature of rocks with a southern exposure remained at all times below 0 °C. For rock surfaces exposed to the north, temperatures rose to 7 °C on clear days, but remained below 0 °C on overcast days. On a windy day, mean rock temperatures were significantly lower. Heat gradients were recorded in the upper 15 mm of the rock substrate. Photosynthetically active solar radiation at the rock surface amounted to over 1,000 μ E m −2 S −1 on an overcast day and to about 1,500 μ E m −2 S −1 on clear days. Approximately 1 % of incident light penetrates the rock to the level of the lichens. Relative humidity inside the rock was generally high and remained at 80 % or more for 5 days following snowfall. Meltwater entering the porous rocks is a water reservoir for the lichens. Measurements on rock samples collected in earlier years at Linnaeus Terrace indicated that the water content of rocks may not stay high at all times. Steep or vertical rock faces where snow cannot accumulate are dry and are not colonized by lichens. Water loss (evaporation) from the rock surface is of the same order of magnitude as that from an open water-saturated system. The results show that both temperature and humidity conditions are significantly more favorable for the life in the lichen zone inside the rock than on the surface. It was estimated tentatively that, on an overcast day, cryptoendolithic lichens may have been photosynthetically active for about 15 h, although these conditions were suboptimal. On a clear and windy day, photosynthesis may have been possible for 11 h, with 4 h optimal activity. On a clear, warm and calm day, the estimates amounted to 13.5 and 6.5 h, respectively.