Effect of Nitrogen on Growth, Yield and Photorespiratory Activity in Spring Wheat

Abstract

Spring wheat plants growing in pots in controlled environment rooms were given extra nitrogen after flag leaf emergence. The effect of nitrogen on growth, yield, the activity of ribulose 1,5–bisphosphate carboxy–lase/oxygenase and the distribution of14C in photorespiratory intermediates and in different parts of the plants was determined. Extra nitrogen increased the movement of 14C to the ear and increased grain yield by 29 per cent, mainly because of an increase in grain number. Though extra nitrogen delayed senescence of the leaves, the growth of the ear in the later stages was not increased in proportion to the extra green area. The relative inefficiency of leaf area with extra nitrogen, which has also been found in the field, was not due to a reduction in photosynthesis per unit leaf area. Nor was there evidence of an increase in photorespiration as reflected by a greater flow of carbon into the photorcspiratory metabolites glycine and serine, or an increase in the activity of ribulose 1,5–bisphosphate oxygenase relative to the carboxylase. We suggest that there may be an increase in the loss of carbon in dark respiration.