Mechanisms of drought response in Thuja occidentalis L. I. Water stress conditioning and osmotic adjustment
1995
Edwards, D.R. (University of Guelph, Guelph, Ontario, Canada.) | Dixon, M.A.
We investigated the extent of osmotic adjustment and changes in transpiration rate that occur in response to repeated cycles of water deficit stress in 6-year-old Thuja occidentalis L. (eastern white cedar) trees. Groups of trees were water-stress conditioned by repeated exposure to predetermined thresholds of nonlethal water stress by withholding water until the predawn water potential fell to -0.9 (mild conditioning) or-1.4 MPa (moderate conditioning). Both the mild and moderate conditioning treatments resulted in a decrease in osmotic potential of 0.08 to 0.20 MPa and 0.11 to 0.28 MPa, respectively, relative to the well-watered controls. Mildly and moderately conditioned trees exhibited an approximately 35 and 50% reduction in cumulative transpiration, respectively, following at least two stress cycles. Transpiration rates of conditioned trees remained below those of the well-watered controls even when water potential integrals were similar. We conclude that the decrease in transpiration rate was more important than osmotic adjustment as a mechanism of response to repeated water stress
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