A series of experiments were conducted to determine the sensitivity of radish to four light alcohols (ethanol, methanol, 2-propanol, and t-butanol) identified as atmospheric contaminants on manned spacecraft. Radish (Raphanus sativus L. `Cherry Bomb' Hybrid II) seedlings were exposed for 5 days to concentrations of 0, 50, 100, 175, 250, and 500 ppm of each alcohol and the effect on seedling growth was used to establish preliminary threshold response values. Results show a general response-pattern for the four alcohol exposures at threshold responses of 10% (T10), 50% (T50) and 90% (T90) reduction in seedling length. There were differences in the response of seedlings to the four alcohols, with the T10 for t-butanol and ethanol (25 to 40 ppm) being 3 to 5× lower than for methanol or 2-propanol (110 to 120 ppm). Ethanol and t-butanol exhibited similar T50 values (150 to 160 ppm). In contrast, T50 for methanol (285 ppm) and 2-propanol (260 ppm) were about 100 ppm higher than for ethanol or t-butanol. Chronic exposures to 400 ppm t-butanol, ethanol or 2-propanol were highly toxic to the plants. Radish was more tolerant of methanol, with T90 of 465 ppm. Seeds did not germinate at the 500 ppm treatment of t-butanol, 2-propanol, or ethanol. There were significant differences in projected performance of plants in different environments, dependent upon the regulatory guidelines used. The use of exposure guidelines for humans is not applicable to plant systems.
Differences between shoots of normal and stagnant 20-year-old lodgepole pine were assessed in an attempt to elucidate possible causes of stagnated growth. Leaves of the stagnant plants are relatively short, narrow and few, and the intemodes between fascicles are short. At least on the site studied, foliar mineral concentration was the same for the two types of plant. Long shoot apical meristems are relatively small in height and diameter. The possibility that the differences reside in the apical meristem, i.e., are epigenetic rather than directly environmentally induced, was tested. Reciprocal grafts of vigorous and stagnant scions onto the two types of rootstock showed, however, that growth assumed that typical of the rootstock by the third growing season, and this was maintained in the subsequent season. This result, and the strong resemblance of stagnant shoots to those resulting from transplant shock, suggest that differences in the form and activity of the root systems is a potential cause of stagnation in lodgepole pine.
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