Respiration rates of red pine along a gradient of gamma radiation following eight years of exposure

Eleven-year-old red pine trees that had lived for eight yr along a gradient of gamma radiation changed little in respiration rates between exposure rates of 1·0–4·0 rads/day. Between 4·0–6·0 rads/day, respiration rates increased by an average of 54 per cent, and between 6·4 and 6·8 rads/day, respiration rates decreased by an average of 26 per cent. The increase in respiration rates may be due to oxygen consuming repair mechanisms. The decrease in respiration rates may result from reduced rates of cell division or reduced activity of growth hormones. The decrease probably did not result from dead tissue comprising part of the sample.