Photosynthesis of a scots pine shoot: Test of a shoot photosynthesis model in a direct radiation field |
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Affiliation: | The Finnish Forest Research Institute, Suonenjoki Research Station, SF-77600 Suonenjoki Finland;University of Helsinki, Department of Silviculture, Unioninkatu 40 B, SF-00170 Helsinki Finland;Institute of Astrophysics and Atmospheric Physics, Estonian Academy of Sciences, Töravere 202444, Tartu, Estonia U.S.S.R.;University of Joensuu, Department of Forestry, P.O. Box 111, SF-80101 Joensuu Finland;University of Helsinki, Botanical Museum, Unioninkatu 44, SF-00170 Helsinki Finland;Forest Ecology, Institute of Terrestrial Ecosystems, Department of Environmental Systems Science, ETH Zurich, Universitätstrasse 16, CH-8092 Zurich, Switzerland |
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Abstract: | The photosynthetic light curves of eight Scots pine (Pinussylvestris L.) shoots, each with a different structure, were measured in a direct radiation field at different positions relative to the radiation beam. Using a model of shoot geometry, the irradiance distributions on the needle surface area of the same shoots were simulated in each position. Using measurements of shoot photosynthesis, the photosynthetic light curve for a needle surface area element (a small area on the needle surface) was estimated indirectly for each shoot. Shoot photosynthesis was then calculated from the estimated photosynthetic light response curve of a needle surface area element and the irradiance distribution on the surface area of needles. Calculated rates for shoot photosynthesis agreed well with the measured rates. The mean irradiance on the needle surface area was the major component causing variation in the light response of a shoot irradiated from different directions, but the shape of the irradiance distribution on the needle surface area had a considerably smaller effect. |
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