Genotypic and nutrition-dependent variation in water use efficiency and photosynthetic activity of leaves in winter wheat (Triticum aestivum L.).

Effects of high and reduced NPK nutrition on the genetic variation of components of water use efficiency at the leaf and whole-plant levels were examined in pot-grown old and modern cultivars of winter wheat (Triticum aestivum L.). At the subsequent growth stages, the photosynthetic rate (A), transpiration rate (E), leaf area (LA) and gas exchange efficiency (A/E) were measured on fully developed 4th, 5th, penultimate and flag leaves. At the plant canopy level, the total amount of water transpired was recorded during the whole life cycle to determine the efficiency of water use in the vegetative (WUEveg) and grain (WUEgen) matter formation. Considerable genotypic differences were found for the characters studied. The limited NPK supply caused a decrease in LA, A and A/E, but contributed to an increase in WUEgen. Examined cultivars (C) did not interact with nutrition levels (N) for these characteristics. However, the position of leaves (L) and the C x L and N x L interactions significantly affected the variance in leaf photosynthetic characteristics. A and A/E were negatively correlated with LA, and the flag leaves were photosynthetically less active and less efficient per unit area than the lower leaves. The whole-plant components of WUE were found to be more genetically stable than the photosynthetic leaf characteristics. Some modern cultivars tended to form leaves of higher A and A/E than the older ones, and this corresponds with a more efficient use of water in grain formation (WUEgen) of the former. Stay-green duration of flag leaves and harvest index showed positive correlations with WUEgen. However, no close associations were noticed between WUE components and stress tolerance, and the modern cultivars were usually less tolerant to NPK shortage.