Physiological‐environmental Interactions in Lichens

Abstract

SUMMARYThe seasonal response matrix of gas exchange and nitrogenase activity in Coltema furfuraceum is presented for a number of factorial combinations of light, thallus temperature (5, I 5, 25 and 30 to 3 5 °C) and thallus water content, throughout the year. The results indicate C. furfuraceum is adapted both to the relatively xeric environment of its corticolous habitat as well as to the low temperatures experienced in its low-arctic environment. Of particular interest is the absence of a summer thermal stress response, which eliminates or severely reduces nitrogenase activity during the summer months in some lichens growing in more southerly localities. Equally, ambient temperatures during the winter, which can drop to minus 41 °C, do not affect nitrogenase activity and confirm the resistance of the nitrogenase enzymes in the intact thallus, to low temperatures.There is a remarkable degree of uniformity in the net photosynthetic response matrix, at most light levels, at all experimental temperatures and at all times of the year. The total absence of seasonal photosynthetic acclimation as well as the seasonal constancy of photosynthetic capacity is discussed in terms of differential strategies in contrasting environments. I N r R O D U C T I O NIn a number of previous papers in this series we have described metabolic changes in net photosynthetic rate, respiration rate and nitrogenase activity on a seasonal basis, for a number of lichen populations (Kershaw, 1977a, b; MacFarlane and Kershaw, 1977, 1980a, b). Similarly Larson (1980) has examined seasonal changes in rates of net photosynthesis and respiration in several species of Umbilicaria.The marked summer decline of nitrogenase activity in Peltigera (MacFarlane and Kershaw, 1977) was shown to be due to summer temperature stress. Conversely, the elimination of nitrogenase activity under the winter snow-pack was shown to be due to the depletion of the carbohydrate pool supplying energy to the reaction in the dark, rather than the direct inactivation of the nitrogenase enzymes by freezing temperatures as had previously been suggested (Alexander and Kallio, 1976; Kallio, Kallio and Rasku, 1976; Crittenden and Kershaw, 1979). MacF'arlane and Kersbaw concluded that low rates of nitrogenase activity under snow cover result from prolonged darkness rather than the prevailing freezing temperatures. Subsequent recovery is equally controlled by radiant energy with temperature playing a subordinate role. Casual observation of an abundance of the lichen Collema furfuraceum, containing Nostoc as a phycobiont, on trees on sand bars in and along the river at Moosonee in north Ontario, offered the means of confirming our previous interpretation of the seasonal changes in nitrogenase activity in other lichens.0028-646>;/K2/()4()72.^ + 12 SO.IOO/O

Growth rate responses of Lobaria pulmonaria to canopy structure in even-aged and old-growth cedar–hemlock forests of central-interior British Columbia, Canada

“…Although rates of net photosynthesis and nitrogen fixation in cyanolichens are generally optimal at temperatures of 20-25 8C or higher (Kershaw, 1977;Kershaw and MacFarlane, 1982;Pannewitz et al, 2000;Sundberg et al, 1997), in many cases hydrated lichen thalli operate under suboptimal temperature and light conditions, reflecting the conditions that often accompany precipitation events, especially in boreal and montane environments (Coxson and Coyle, 2003;Palmqvist and Sundberg, 2000). These limitations on lichen growth rates were evident in L. pulmonaria thalli from our inland rainforest study sites.…”

Terrestrial cryptogams of pinyon-juniper woodlands in the Southwestern United States : a review /

“…A complete absence of nitrogenase activity has been reported under snow cover (Kershaw 1985). But Kershaw and MacFarlane (1982) have measured nitrogenase activity of Collema furfuraceum at thallus temperatures as low as -40°C.…”

Seasonal Photosynthetic Capacity Changes in Lichens: A Provisional Mechanistic Interpretation

“…The winter state may be signalled by either an increase of respiration rate as in Umbilicaria deusta and U. mammulata and with or without a corresponding photosynthetic capacity change; or it may be signalled by a decrease of winter respiration rate as in U. vellea which also has been found in Cladonia rangiferina (Tegler & Kershaw 1980); or there may be a marked change of photosynthetic capacity at all temperatures as found in Peltigera praetextata, P. polydactyla (Kershaw 19776), and Umbilicaria papulosa (Larson 1980) without any concurrent change in respiration rate. Finally, there may be no apparent change in winter rates of CO 2 gas-exchange, a characteristic which is also found in Collema furfuraceum (Kershaw & MacFarlane 1982).…”