Relative contribution of laminae to total carbon dioxide fixation in wheat in response to nitrogen

Relative contribution of the main shoot laminae towards the total carbon dioxide fixed by the main shoot was examined in wheat cultivars Uniculm Gigas (V₁) and Kalyansona (V₂). These cultivars were grown in pots at two levels of nitrogen, viz. 30 (N₁, sub-optimal) and 120 (N₂, optimal) kg ha⁻¹. Photosynthetic rates (Pn) and lamina area at each insertion level were measured at weekly interval throughout the ontogeny. Sub-optimal level of nitrogen significantly reduced the area of the upper laminae, particularly penultimate and flag lamina, in both the cultivars. Pn rate of these two laminae was also reduced under sub-optimal N in the cv Kalyansona. These reductions were reflected in the grain yield. At optimal N level, the upper laminae make significant contribution to the total carbon dioxide fixed by the plant.