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Photosynthesis and Photorespiration in Two Clones of Orchardgrass¹

We measured photosynthesis and photorespiration of two selected clones of orchardgrass Dactylis glomerata L., at 1, 2, 5, 11, 32, and 52 klux of light. Clone A7 exceeded clone P3 by 50% in photosynthesis and 40% in photorespiration at saturating light intensity. The CO₂ compensation point was identical for both clones. Photosynthesis and photorespiration increased with increasing light; however, no photorespiration was observed at a light intensity of 2 klux or lower, and saturation occurred at 11 klux. Clone P3, with the lowest photosynthetic rate, had the greatest amount of apparent photorespiratory substrate. Photosynthesis was not inversely related to photorespiration but was inversely related to photorespiratory substrate. Selecting orchardgrass for photosynthetic efficiency should be possible.

Key Words: Dactylis glomerata L. • CO₂ compensation point

² Research Agronomist, Agricultural Research Technician, and Research Agronomist, respectively, Crops Research Division, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705.

³ Now Assistant Professor, Agronomy Department, Iowa State University, Ames, Iowa 50010.

Received for publication April 11, 1970.