Application of Stable Carbon Isotopes in Investigating Water Use Efficiency of Summer Maize

¹³ C discrimination (Δ ¹³ C) is considered an efficient indicator reflecting the integrated responses of plant photosynthesis and transpiration to soil water availability. However, the relations between water use efficiency and Δ ¹³ C of summer maize were unclear. Toward addressing these ends, here, we selected 3 genotypes with different drought resistance of summer maize (weak drought-resistance ability, WD; middle drought-resistance ability, MD; and strong drought-resistance ability, SD) and investigated the changes of water-use characteristic, leaf Δ ¹³ C and their relations. The results showed that in the vegetative stage of summer maize, the water consumption of SD genotype is the smallest and the highest value appeared in the WD genotype. However, by flowering-filling stage, the water consumption of SD genotype significantly became the highest. WD genotype has the highest instantaneous leaves water use efficiency, mainly attributed to relating higher leaf area index; but the highest water use efficiency at the grain yield level was appeared in MD genotype resulting from higher SPAD and transport efficiency of biomass to grains. Leaf Δ ¹³ C was significantly positively correlated with photosynthetic rate, transpiration rate, and soil water storage, but significantly negatively proportional to water use efficiency at leaf and grain levels. Our results indicated that Δ ¹³ C was mainly influenced by photosynthetic rate, soil water storage, and transpiration rate, and was negatively correlated with WUE, which can be used as a useful indicator of WUE.