Effects of elevated carbon dioxide and water deficit interaction on sugarcane water use and yield: an experimental and crop modeling study
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Climate change is predicted to impact sugarcane production globally. Models like Canesim® can be used to predict these impacts and plan adaptation strategies. To enable assessment of these impacts, Canesim® requires testing with scenarios involving elevated CO2 (ca) and soil water deficit (SWD) interactions. It is hypothesized that negative consequences of SWD on plant productivity would be mitigated under elevated ca. This mitigation may be ascribed to plant acclimation through reduced stomatal conductance (gs), transpiration rate (E), and increased water use efficiency (WUE), which may buffer transient periods of drought stress. This will in turn stimulate the biomass and sucrose yield via soil moisture stress avoidance. An open-top chamber experiment was conducted with potted sugarcane plants grown under ambient ca*well-watered, ambient ca*SWD, elevated ca*well-watered and elevated ca*SWD conditions. The CO2 levels were controlled at 400 ?mol mol-1 (ambient ca) in six open-top chambers and 750 ?mol mol-1 (elevated ca) in the other six open-top chambers for a period of seven months. The leaf level photosynthesis, transpiration and yield were measured. The elevated ca*well-watered, elevated ca*SWD and ambient ca*SWD treatments respectively recorded altered carbon assimilation rate (-2%, -17%, -37%), stomatal conductance (-51%, -61%, -41%), transpiration rate (-29%, -38%, -25%), water use efficiency (+35%, +30%, -16%) and cane yield (+18%, -17%, -50%) relative to ambient ca*well-watered treatment. The Canesim® model simulated altered cane yield (+8%, -10%, -20%) in the elevated ca*well-watered, elevated ca*SWD and ambient ca*SWD treatments relative to ambient ca*well-watered treatment. The underestimation of the magnitude of yield responses to elevated ca and SWD may be due to difficulties in representing pot and chamber conditions in the model. This study suggest that elevated ca alleviates SWD effects, resulting in improved crop productivity. Further studies need to explore the parameterization of the model to account for a pot chamber environment and also to increase the stomatal conductance effect under SWD. This will enable more precise exploration of sugarcane plant response to predicted future climate change scenarios.