Effects of Acute Gamma Radiation and Winter Temperature-Light Conditions on Photosynthesis of Cladonia mitis

Abstract

The rate of photosynthesis (14C incorporation) of Cladonia mitis Sandst. was found to be affected by both gamma radiation and winter conditions. Gamma radiation had the greater effect, reducing 14C incorporation to the level of dead podetia. Photosynthesis did continue under the law light (5 f.c.) and temperature (30C) conditions, but at very reduced levels. Light appeared to be the limiting factor of the winter conditions. In a series of continuing experiments with Cladonia mitis Sandst. and gamma radia- tion (Erbisch, 1970, 1971, 1972; Erbisch & Kalosis, 1973) it has been found that: 1) respiration of acutely irradiated (through 1000 krad) podetia was the same as the non-irradiated control, 2) up to six weeks after acute irradiation less than 10% of the algal cells seemed to be damaged, 3) podetia appeared to be undamaged through one sum- mer of chronic gamma radiation-even those receiving 900+ rad/day, and 4) in the spring following a summer of chronic radiation those lichens which had received more than 70 krad appeared damaged. These data tend to indicate that C. mitis can re- ceive large doses of chronic and/or acute gamma radiation and not manifest damage until some later time. This manifestation of damage usually occurred after a prolonged period suitable for growth. In the field this suitable period was the spring following the irradiation period. Perhaps the podetial damage manifested is partially the result of insufficient ma- terials at the time of growth because of reduced photosynthesis. Although algal cells appear to be undamaged the photosynthetic apparatus may be damaged thereby re- ducing photosynthesis. Lichens irradiated and replaced into the field only exhibited damage in spring. Also Cladonia podetia, when dug out of the snow, were unfrozen, moist and, perhaps, phys- iologically active. If enough light penetrated the snow cover, these lichens may photo- synthesize, building up a supply of raw materials which would be used for growth in the spring. Bliss and Hadley (1964) found that optimum photosynthetic values for arctic lichens occurred at low temperatures. If C. mitis has a photosynthetic pattern similar to arctic