Crop productivity and water use efficiency: The role of carbon isotope discrimination technique

Abstract

At a time when global population continues to increase, global agriculture now accounts for 70% of the amount of water used on earth and crop losses due to water loss are much higher than crop losses due to any other causes. Reliable selection of crop varieties or genotypes with increased grain yield is essential both under irrigated and rain-fed conditions, due to water shortage commonly experienced in many environments. This can be obtained by increasing crop water use efficiency (WUE) either by breeding, or by soil, water and crop management. WUE can be enhanced by reducing water losses (runoff, drainage, evaporation), thus increasing the proportion of the water used by the crop. There is, indeed, a clear relationship between the amount of water transpired and yield across a diverse range of crop species. The carbon isotope discrimination technique has been proposed by several authors as a mean of selecting cultivars with improved WUE. Carbon isotope discrimination (Δ) of plant tissues (leaf or grain) has been shown to correlate negatively with transpiration efficiency and positively with grain yield in a wide range of crops. In the present chapter, recent progress in improving crops for yield and water-use efficiency using the carbon isotope discrimination technique are reviewed and some possible avenues for making further advances are discussed. The review describes the basis of carbon discrimination in C3 and C4 crops with a special emphasis on cereals, dominant food crops grown in irrigated and rain-fed areas.