Estimate of Water Flow in Douglas-Fir Seedlings

A study with Douglas—fir (Pseudotsuga menziesii [mirb.] Franco) seedlings in a controlled—environment chamber demonstrated that measurements of sap flow by the sap—velocity meter provide an accurate estimate of transpiration (correlation coefficient r = .91). Thus the meter is a useful tool in both ecological and physiological work with seedlings. Xylem sap pressure, relative stomatal aperture, transpiration, and sap flow were determined in both the light and the dark under various conditions of air temperature, soil water content, and relative humidity. Sap flow was observed to lag behind transpiration from 15 to 45 min. Preconditioning a seedling in a controlled environment prior to experimental observations can alter its response. See full-text article at JSTOR