Effect of Chronic Gamma Radiation on Parmelia subaurifera in the Enterprise Radiation Forest

Abstract

In the Enterprise, Wisconsin, Radiation Forest thalli of Parmelia subaurifera Nyl. received varying doses of gamma radiation (137Cs) during the summer of 1972. Thalli which received 122,272 r exhibited radiation damage by the end of the radiation period. The damage was seen in the decrease of thalloid algal cells, bleaching of the thallus, upper cortex breakup and, eventually, the disappearance of the thallus. Thalli receiving 78,797 r initially exhibited temporary damage in the destruction of some algal cells and cessation of thallus growth. By 1973 algal cells appeared normal and by 1974 growth had resumed. No damage was seen in thalli which had received 66,570 r or less. The North Central Forest Experiment Station, at Rhinelander, Wisconsin, began a study in 1969 on the effects of gamma radiation in typical northern forest ecosystems (the Enterprise, Wisconsin, Radiation Forest). In 1972 a 10,000 Ci 137Cs radiation source was placed into operation. The forest ecosystems were irradiated 20 h/day for a total of 166 days and 2717 h. For more detail on the radiation site and preirradiation studies see Rudolph (1974) and for the results of the radiation studies see Zavitkovski (1977). This radiation site provided an opportunity to study the effects of gamma radiation on lichens in their natural habitat. When the study was initiated only two published studies were found which dealt with gamma radiation and lichens in natural habitats. One by Brodo (1964) indicated that the lichen flora was affected more by microclimate changes than radiation damage; whereas Woodwell and Gannutz (1967) indicated that gamma radiation had a greater effect on lichens than environmental conditions. The study undertaken in the Enterprise Radiation Forest was designed to consider both ecological and radiological effects on lichens. After examining the lichen flora in the radiation site, Parmelia sulcata was chosen as the primary study organism because it was found throughout the radiation and control areas (cf. Erbisch, 1974, 1977). Parmelia subaurifera Nyl. occurred on many of the same tree sites with P. sulcata; consequently it was also examined to determine the effects of both gamma radiation and environmental change. 'The work reported here was supported by the U.S. Energy Research and Development Administration under contract E(11-1)-2085. Appreciation is expressed for the assistance received from the personnel of the North Central Forest Experiment Station, Rhinelander, Wisconsin, especially Dr. J. Zavitkovski. I wish to thank E. M. Erbisch for her assistance in this project. 2 Department of Biological Sciences, Michigan Technological University, Houghton, MI 49931. 0007-2745/78/137-143$0.95/0 This content downloaded from 207.46.13.158 on Sun, 10 Apr 2016 06:23:03 UTC All use subject to http://about.jstor.org/terms 138 THE BRYOLOGIST [Volume 81 TABLE 1. Location and radiation data for the Parmelia subaurifera Nyl. thalli on Acer rubrum studied in the Enterprise Radiation Forest.