Ethanol accumulation in drought-stressed conifer seedlings

In this study, we investigated the effect of drought stress on ethanol production and accumulation in tissues from seedlings of three conifers (Douglas-fir, lodgepole pine, and ponderosa pine) with increasing degrees of tolerance to drought stress, respectively. Significant ethanol accumulation was only observed in their aerial tissues when severely stressed (water potential < -3.0 MPa or water content < 0.4 g g(-1) dry mass), with needles accumulating greater quantities than the sapwood or phloem. All species had the same predawn water potentials when sampled, but they were experiencing different levels of stress based on their foliar water contents. Severely stressed Douglas-fir contained higher ethanol and lower water contents (except phloem) than the more drought-tolerant ponderosa pine seedlings. Lodgepole pine with intermediate drought tolerance tended to have intermediate quantities of both components. The mechanistic basis of ethanol accumulation associated with drought stress remains to be determined, especially in larger trees. We speculate that increased levels of in situ ethanol synthesis in seedlings may be associated with heat injury (e. g., membrane damage) due to a reduction in transpirational cooling after stomatal closure. Drought-induced hypoxia may also contribute to ethanol accumulation in the sapwood.