Effects of Nitrogen Fertilization on Growth, Leaf Area, and Photosynthesis Rate in Douglas-Fir
Abstract: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.
Document Type: Journal Article
Affiliations: Research Scientist, Forest Research Laboratory, Dept. of Fisheries and Forestry, Victoria, B. C.
Publication date: 1969-06-01
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