Physiology and growth of Douglas-fir seedlings treated with ethanol solutions

Applying 1, 5, 10, and 20% solutions of ethanol to the roots of Douglas-fir (Pseudotsuga menziesii [Mirb.] France) seedlings three times a week was de leterious to their physiology and growth. Ethanol concentrations of 10% or higher were lethal within a week of treatment initiation, while the 5% solu tion was lethal to seedlings at similar to 8 weeks. Seedlings treated with the 1% solution were alive at 8 weeks, but showed signs of physiological de cline. If Douglas-fir seedlings have a tolerance threshold for ethanol solu tions applied to their roots, it appears to be at a concentration below 1%. Ethanol moved up the stems and into needles, yielding concentrations in th e stems 9 times higher than in needles. Ethanol vapors in the atmosphere su rrounding seedlings readily diffused into needles, but not into stems. Afte r 1 week of:treatments, net photosynthesis, stomatal conductance, and trans piration declined as ethanol concentrations increased. However, seedlings t reated with the control (0%) and 1% ethanol solutions had the same xylem wa ter potentials, which were higher than for seedlings treated with the 5% so lutions. High ethanol concentrations (greater than or equal to 1%) may have damaged membranes involved in photosynthesis and stomatal function thereby causing the observed decline in net photosynthesis and stomatal conductanc e. At:concentrations greater than or equal to 5%, water uptake was impaired , suggesting that root membranes may have been damaged. (C) 2000 Elsevier S cience Ireland Ltd. All rights reserved.