Differential response of two wheat genotypes to nitrogen supply. I. Ontogenic changes in laminae growth and photosynthesis

Abstract

Two wheat genotypes viz. Uniculm 'gigas' (VI) and Kalyansona (V2) were raised till maturity with low (N1) and adequate (N2) nitrogen levels supplied at 30 and 120kg ha^-1, respectively. Laminae, numbering 1-8 on the main shoot, were examined for various parameters at weekly intervals from emergence through senescence. N1 resulted in gradual reduction in laminae growth from 5th leaf onwards with maximum effect on flag and penultimate laminae of both the genotypes. Chlorophyll concentration, soluble protein, rubisco concentration and rubisco activity in response to low N supply was reduced in the top two laminae in V2. Pn rate varied little with leaf position in wheat at adequate N supply. In V2, low N supply resulted in the reduction of laminae N content by about 25% with corresponding reduction in Pn rates in the penultimate and flag laminae. VI, in contrast, exhibited no significant change in leaf N concentration and hence maintained similar Pn rates at both levels of N supply throughout the ontogeny. It is concluded that the two genotypes responded differently to N supply in relation to laminae growth and photosynthesis. Uniculm 'Gigas' (VI) responded to low N with large reduction in laminae size, adequately maintaining the metabolic constituents such as chlorophyll, soluble protein, rubisco and laminae N concentration and Kalyansona (V2), in contrast, responded with small changes in laminae size and greater reduction in synthesis and maintenance of the metabolic constituents.