Stable Carbon Isotopes in Zea mays
The increasing demand for food production and predicted climate change scenarios highlight the need for improvements in crop sustainability. The efficient use of water will become increasingly important for rainfed agricultural crops even in fertile regions that have historically received ample precipitation. Improvements in water-use efficiency in Zea mays have been limited, and warrants a renewed effort aided by molecular breeding approaches. Progress has been constrained by the difficulty of measuring water-use in a field environment. The stable carbon isotope composition ({delta}13C) of the leaf has been proposed as an integrated signature of carbon fixation with a link to stomatal conductance. However, additional factors affecting leaf {delta}13C exist, and a limited number of studies have explored this trait in Z. mays. Here we present an extensive characterization of leaf {delta}13C in Z. mays. Significant variation in leaf {delta}13C exists across diverse lines of Z. mays, which we show to be heritable across several environments.\n\nFurthermore, we examine temporal and spatial variation in leaf {delta}13C to determine the optimum sampling time to maximize the use of leaf {delta}13C as a trait. Finally, our results demonstrate the relationship between transpiration and leaf {delta}13C in the field and the greenhouse. Decreasing transpiration and soil moisture are associated with decreasing leaf {delta}13C. Taken together these results outline a strategy for using leaf {delta}13C and reveal its usefulness as a measure of transpiration efficiency under well-watered conditions rather than a predictor of performance under drought.\n\nSignificance StatementThis study identifies sources of variation in stable carbon isotopes of maize leaves and establishes the framework for connecting leaf {delta}13C and transpiration efficiency.