Field Measurments of Carbon Dixoide Exchange by Pinus Rigida Trees Exposed to Chronic Gamma Irradiation

Rates of CO2 absorption in Pinus rigida trees exposed to chronic gamma irradiation were depressed during midwinter and recovered during the spring. Net photosynthesis occurred at low rates throughout the winter when light intensity was high and air temperature in the chambers was within 1—2°C of freezing or higher. Irradiation first reduced rates of CO2 absorption to low but positive levels which persisted briefly until the leaves lost chlorophyll and turned brown. Trees exposed at 1,300 r/day succumbed after total exposure to more than 120,000 r, while trees exposed to 30 r/day succumbed after about 6,300 r. The processes involved in CO2 exchange are apparently resistant to short—term damage from chronic exposures in the range of 30—1,300 r/day, and measurement of IO2 exchange is not a sensitive technique for measurement of radiation damage to plants. See full-text article at JSTOR