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Some Temperature and Light Effects in the Growth of Jeffrey Pine Seedlings

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Abstract:

Pinus jeffreyi (Grev. and Balf.) seedlings from a single-tree seed lot were grown in 15 controlled temperature environments. Two of the temperature conditions were duplicated under high and low intensities. Most of the tests were made in rooms with low intensity light of about 500 foot-candles. High intensity light conditions were obtained in temperature controlled greenhouses. The coefficient of variability for trees grown under artificial light averaged 22 percent for fresh weight of tops and for dry weight of tops, roots, and total plant. Most of the variability was estimated to be due to genetic differences between the plants. Total daily degree-hours appeared to be the dominant temperature measure in determining maximum dry weight production. Best growth was attained with 300 to 400 daily degree-hours. Best root growth was obtained under a smaller number of daily degree-hours than was required for best top growth. Warm nights and cool days favored root growth over top growth. Wet weight and dry weight formed almost a straight line relationship for plants grown under low light intensity, irrespective of the temperature conditions. Terminal bud development required about 240 daily degree-hours, while secondary needle formation was stimulated by high day and low night temperatures, and lateral branches developed at day temperatures above 17°C irrespective of night temperature. Light was used more efficiently at low intensity than at high intensity. Problems involved in comparing chamber and greenhouse results were discussed.

Document Type: Journal Article

Affiliations: Plant Physiologist, Pacific Southwest For. and Rge. Expt. Sta., Forest Service, U. S. Dept. Agric., and Senior Research Fellow, The California Inst. of Technology, Pasadena

Publication date: June 1, 1963

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