Chapter 10 - 2 Temperature : Cold

Figure 1. Racomitrium heterostichum mostly imbedded in ice while some branches are free and available for photosynthesis. In general, bryophytes seem able to withstand cold in the leafy state much better than their tracheophyte counterparts. Ochi (1952) found that most mosses (18 species tested) were resistant to cold to-20°C. Seven of these species were resistant to-27°C. He was unable to find any trend in relationships to osmotic value, permeability, or seasonal fluctuations. Ochi's results support the later statement of Kallio and Heinonen (1973), that Racomitrium lanuginosum, a cosmopolitan moss, is pre-adapted to its abode in the Arctic and Antarctic (see Table 1; Figure 7) and suggest that such pre-adaptation may be a common feature of bryophytes. This contention is supported by the low lethal temperatures for bryophytes in the tropics (Table 2). Surprisingly, Arctic liverworts are not so cold resistant. Among the nine species tested by Biebl (1968), seven were mostly dead at-16ºC, with only Lophozia hatcheri and Chandonanthus setiformis surviving well. The moss Aulacomnium turgidum also survived at-16ºC. All species survived-6ºC. But these were July responses in Greenland; a quite different picture might emerge in winter. On the other hand, all of them survived up to 42ºC for half an hour, but twelve-hour exposures killed parts of most of them, the same seven, at 38ºC. Aulacomnium turgidum survived up to 48ºC for half an hour and up to 40ºC for twelve hours. This supports the hypothesis that low temperature survival is coupled with high temperature survival. Tropical mosses seemed little different. After 24 hours of exposure, Homaliodendron flabellatum and Leucoloma amoenervis survived-14ºC and Schistochila commutata survived-11ºC (Biebl 1967). Plagiochila, Metzgeria (Figure 2), and Bryum species each survived to at least-4ºC. Try doing that to a tropical Maranta.