Carbon isotope discrimination as indicator of water-use efficiency of spring wheat as affected by salinity and gypsum addition

High water-use efficiency and salinity tolerance are two major parameters in plant breeding programs aimed at developing crop species for semi-arid salt-affected areas. Recent studies have shown that carbon isotope composition of a plant may be a useful criterion to assess water use efficiency in C3 plants and, therefore, an effective method to screen genotypes for improved drought resistance. In this pot experiment, we studied the relationships between C-13 isotope discrimination (Delta) and water use efficiency of spring wheat in 4 salt affected gypsiferous soils. The soils consisted of a non-saline gypsum-free soil (S0G0), and three others contained gypsum (S0G1), salt (S1G0) and gypsum and salt (S1G1). Fertilizer N use efficiency was calculated using the N-15 isotopic dilution techniques. The ratio of total dry matter produced to amount of water consumed was used to calculate the water-use efficiency. Molar ratios of C-13/C-12 in plant material and in the atmosphere were used to estimate the carbon isotope discrimination. Mixing gypsum with the soil reduced sodium adsorption ratio and had a positive effect on the measured chemical and physical properties of the soils. Plants grown in S1G0 died before reaching physiological maturity. Plants grown in S0G1 soil had the highest dry matter production, water use efficiency and fertilizer use efficiency followed by those grown in S0G0. The data suggest that C-13 isotope discrimination can be an effective method to screen genotypes of wheat with a high drought resistance in soils affected by salinity and gypsum addition. In this study, a high negative correlation was observed between C-13 isotope discrimination and nitrogen use efficiency of wheat.