Nitrogen Fixation by Lichens

Lichens with N2-fixing blue-green algae as phycobionts or cephalodia have the ability to fix N2 from the air. This was demonstrated by using 15N-enriched nitrogen in laboratory experiments (Bond and Scott 1955, Watanabe and Kiohara 1963, Rogers et al. 1966, Millbank and Kershaw 1969) and in situ (Fogg and Stewart 1968). The present investigation gives further information about the extent of N2 fixation occurring in phycobionts and also about the ability of the lichens to resume N2 fixation after varied periods of drought. The determinations of the capacity of N2 fixation are carried out by using the acetylene reduction technique. Most lichens are very resistant to desiccation. They rapidly recover full activity of photosynthesis and respiration when moistened after a prolonged dry period. The length of the dry period which the lichens can endure, depends upon several factors. One of them is the nutritional state before desiccation, another the conditions of storage. In addition, the environmental conditions in which the lichens are growing influence their ability of surviving long dry periods. Generally, the lichens can withstand dry periods far longer than what they