Effects of Container Density and Plant Water Stress on Growth and Cold Hardiness of Douglas-fir Seedlings
Four thousand Douglas-fir seedlings were grown in a greenhouse for 5 months in 45 ml plastic containers at densities of 270, 540, 810, and 1080 plants m-2. Those grown at lower densities were shorter and thicker stemmed with greater shoot and root dry weights, reduced leaf-water contents, and lower shoot-root ratios; they also exhibited a greater degree of cold hardiness. Compared with densely grown seedlings, those at low densities also received ten times more photosynthetically active radiation on their lower needles; their average midday water potential was three bars lower, and the average daytime soil temperature was 3°C higher. Lowering the xylem water potential of high-density seedlings from -6.5 to -12 bars by restricting watering during the growth period increased their subsequent ability to cold-harden, but decreased shoot and root growth and accelerated bud-set. Forest Sci. 22:167-172.
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