Photosynthesis of Ears and Flag Leaves of Wheat and Barley

Abstract

Immediately after anthesis ears of spring wheat absorbed less than 0.5 mg CO₂, per hour in daylight and later evolved CO₂, in the light and in the dark. The rate of apparent photosynthesis of the combined flag-leaf lamina and sheath and peduncle (collectively called flag leaf) of two spring wheat varieties, Atle and Jufy I, was 3–4 mg per hour; the rates of the flag leaf and the ear of two spring barleys, Plumage Archer and Proctor, were each about 1 mg per hour. The gas exchange of ears and flag leaves between ear emergence and maturity accounted for most of the final grain dry weight. The CO₂, fixed by the wheat ear was equivalent to between 17 and 30 per cent of the grain weight, but more than this was lost by respiration, so assimilation in the flag leaf was equivalent to 110–20 per cent of the final grain weight. In barley, photosynthesis in the flag leaf and the net CO₂ uptake by the ear each provided about half of the carbohydrate in the grain. Barley ears photosynthesized more than wheat ears because of their greater surface, and flag leaves of wheat photosynthesized more than those of barley because they had more surface and a slightly greater rate of photosynthesis per dm².