Water relations in lichens at subzero temperatures: structural changes and carbon dioxide exchange in the lichen Umbilicaria aprina from continental Antarctica

Abstract

SUMMARY Photosynthetic activity and structural changes at subzero temperatures were monitored in the foliose lichen Umbilicaria aprina Nyl. from continental Antarctica. Carbon dioxide gas exchange measurements revealed that net photosynthesis and dark respiration occurred at subzero temperatures regardless of whether a lichen thallus saturated with liquid water was exposed to subzero temperatures, or if a dry thallus was re‐hydrated only from snow at subzero temperatures. When water‐saturated thalli of U. aprina were slowly cooled at subzero temperatures ice nucleation activity could be detected at — 5·4 °C, indicating extracellular freezing of water. Using low‐temperature scanning electron microscopy (LTSEM) it was demonstrated that extracellular ice formation leads to cytorrhysis in the photobiont cells and to cavitation in the mycobiont cells. Both processes were reversible if the lichen thallus was re‐warmed. When dry lichen thalli were covered with snow at subzero temperatures a substantial re‐hydration from snow could be observed in LTSEM micrographs and measured gravimetrically. The final thallus water content was strongly dependent on the temperature regime and gave water contents between 20% d. wt at — 21 °C and 56% d. wt at —4·5 °C after 16 h exposure. Carbon dioxide gas exchange measurements revealed that metabolic activity was initiated during re‐hydration from snow at subzero temperatures. It is proposed that water uptake from snow at subzero temperatures occurs in the gaseous phase and depends only on the temperature‐related differences in water potential between the cell contents and the surrounding atmosphere in equilibrium with snow. Photosynthetic activity and re‐hydration from snow at subzero temperatures are of great ecological importance for primary production in extreme environments such as Antarctica where metabolic activity is severely limited by water availability and low temperatures.

Earth as a Tool for Astrobiology—A European Perspective

“…One example used in ecological field campaigns are the measurements on metabolic activity such as measuring methane production by methanogens (Wagner et al 2005(Wagner et al , 2007 or photosynthetic activity by phototrophs like cyanobacteria, alga and lichens (Lange 1969;Lange et al 1970;Schroeter et al 1994;Schroeter and Scheidegger 1995;Pannewitz et al 2003). Also, reproduction expressed by the growth rate may be recorded, which might take several years of continuously monitoring the selected field sites in order to obtain measurement results over longer time scales.…”

Habitat stress initiates changes in composition, CO2 gas exchange and C-allocation as life traits in biological soil crusts

“…The possibility of activation by water vapour alone is controversial for lichens in Antarctica. It has been experimentally demonstrated that some Antarctic lichens can reactivate from water vapour alone (Kappen, 1993) and Schroeter and Scheidegger (1995) showed the Antarctic lichen Umbilicaria aprina Nyl. being activated by water uptake in the gaseous phase from snow at subzero temperatures.…”

The Effect of Water Accessible Paramagnetic Ions on Subcellular Structures Formed in Developing Wheat Photosynthetic Membranes as Observed by NMR and by Sorption Isotherm

“…Apart from number of species which are tolerant to a mild water deficit, there also exist organisms resistant to deep desiccation (and frost), e.g. resurrection plants [2,3] and lichens [4][5][6][7][8].…”