The Physiology and Stability of Leaf Carbon Isotope Discrimination as a Measure of Water-Use Efficiency in Barley on the Canadian Prairies

Temporal and seasonal water deficit is one of the major factors limiting crop yield on the Canadian prairie. Selection for low carbon isotope discrimination (Delta 13C) or high water-use efficiency (WUE) can lead to improved yield in some environments. To understand better the physiology and WUE of barley under drought conditions on the Canadian prairie, 12 barley (Hordeum vulgare L.) genotypes with contrasting levels of leaf Delta 13C were investigated for performance stability across locations and years in Alberta, Canada. Four of those genotypes ('CDC Cowboy', 'Niobe', '170011' and 'Kasota') were also grown in the greenhouse under well-watered and water-deficit conditions to examine genotypic variations in leaf Delta 13C, WUE, gas exchange parameters and specific leaf area (SLA). The water-deficit treatment was imposed at the jointing stage for 10 days followed by re-watering to pre-deficit level. Genotypic ranking in leaf Delta 13C was highly consistent, with '170011', 'CDC Cowboy' and 'W89001002003' being the lowest and 'Kasota''160049' and 'H93174006' being the highest leaf Delta 13C. Under field and greenhouse (well-watered) conditions, leaf Delta 13C was significantly correlated with stomatal conductance (g(s)). Water deficit significantly increased WUE, with 'CDC Cowboy'- a low leaf Delta 13C genotype with significantly higher WUE and lower percentage decline in assimilation rate (A) and g(s) than the other three genotypes ('Niobe', '170011' and 'Kasota'). We conclude that leaf Delta 13C is a stable trait in the genotypes evaluated. Low leaf Delta 13C of 'CDC Cowboy' was achieved by maintaining a high A and a low g(s), with comparable biomass and grain yield to genotypes showing a high g(s) under field conditions; hence, selection for a low leaf Delta 13C genotype such as 'CDC Cowboy' maybe important for maintaining productivity and yield stability under water-limited conditions on the Canadian prairie.