Simulated Fallout Studies in Conifers - A Preliminary Report

Abstract

Dry seed and 1-year old dormant seedlings for the following species: black spruce, jack pine, red pine, Scotch pine, white spruce and white pine were exposed to irradiation to simulate the gamma component in an early fallout field over a period of 96 h (t10-t106). Seven total dosages ranging from 452 R to 8640 R were employed and the dose-rate (Rt) was made to vary as a power function of time where Rt = R10 t−1.2. A comparable group received the same total dosages over 96 h but at a constant rate. Germination was higher for all speciesunder laboratory conditions than in the field where survival of seedlings from irradiated seed was scored 4 months after irradiation (Sg). The LD100/30 for seeds ranged from 3260 R for white pine to 8640 R for black spruce with the exception of jack pine where germination occurred at all dosages employed. Constant and fallout dose regimes gave comparable results with the exception of Scotch pine and red pine. The LD100/120 for field-grown seeds varied from 1720 R for white pine to 4730 R for jack pine. Fallout and constant rate regimes gave comparable results with the exception of Scotch pine and white pine. One-year-old seedlings survived higher dosages than did irradiated seed scored at 4 months after irradiation. The LD100/120 for the constant rate regime varied from 3260 R for white spruce to 8640 R for jack pine. Comparable results were obtained under the fallout regime for white pine and white spruce, however with jack pine, red pine and Scotch pine lower total dosages produced an LD100/120 under fallout than under the constant-rate regime. In the case of Scotch pine and jack pine other parameters of radiation injury, e.g. fresh and dry weights, seedling lengths, root and stem caliper measurements, supported the aforementioned findings.