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Effects of Nitrogen Fertilization on Growth, Leaf Area, and Photosynthesis Rate in Douglas-Fir

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A 20-year-old stand of Douglas-fir was fertilized with nitrogen in 1964 and again in 1966. The basal area increment, stem height, and branch length increased markedly as compared with the growth of unfertilized trees. Nitrogen increased leaf length and width, the number of leaves per shoot, first-order branch length, and number of second-order lateral branches produced. Measurements in August and September 1967, under near optimum conditions of light intensity, temperature, and water supply, showed no difference in the photosynthetic rate between treated and control trees. In both groups this rate decreased with increase in leaf age through the 5th year. The response of photosynthesis to light intensity, and the average rate of dark respiration for different aged leaves were also similar for both groups. There are indirect indications, however, that the increased foliage area is not a full explanation for greater growth after fertilization. An optimum leaf area per tree was attained 2 years after fertilization, and a further increase in the following years had no effect on stem growth.

Keywords: Pseudotsuga menziesii; respiration

Document Type: Journal Article

Affiliations: Research Scientist, Forest Research Laboratory, Dept. of Fisheries and Forestry, Victoria, B. C.

Publication date: 1969-06-01

More about this publication?
  • Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
    Forest Science is published bimonthly in February, April, June, August, October, and December.

    2015 Impact Factor: 1.702
    Ranking: 16 of 66 in forestry

    Average time from submission to first decision: 62.5 days*
    June 1, 2016 to Feb. 28, 2017

    Also published by SAF:
    Journal of Forestry
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