Effects of radiation from 14CO2 absorbed by Pinus strobus L. seedlings during photosynthesis on their subsequent growth and metabolism.

Several times during the year, white pine seedlings were placed in a closed system and each plant was permitted to photo-assimilate 400–500 μCi of 14CO2. At various periods of time after photo-assimilation, the fresh weight, apparent photosynthesis, dark respiration, and distribution of absorbed 14C throughout the seedlings were determined. The location and magnitude of depressed growth caused by the radiation from the incorporated 14C varied with the time of year when photo-assimilation occurred.When 14CO2 photo-assimilation occurred in May and June, suppression of growth was the greatest in the new shoots, whereas when photo-assimilation occurred in the fall, the suppression of growth was more pronounced in the roots. Seedlings which photo-assimilated 14CO2 in the fall appeared normal during winter but their buds failed to develop into new shoots the following spring.It is also suggested that a decrease in the rate of apparent photosynthesis may be used as an indicator of radiation damage brought about ...