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Summary

The influence of a long term snowcover on the rates of nitrogenase activity in the lichens Peltigera canina var. praetextata and P. canina var. rufescens has been investigated. In accordance with the existing literature, only very low rates of nitrogenase activity could be detected after several months of snowcover. These low rates of activity result from prolonged darkness rather than an inactivation of the nitrogenase enzyme by low temperature. The subsequent recovery of nitrogenase activity after snowmelt is very largely controlled by the presence of radiant energy with temperature playing a subordinate role.