The CERES-wheat crop simulation model was used to estimate the changes in phenological development and yield production of spring wheat (Triticum aestivum L., cv. Polkka) under different temperature and CO2 growing conditions. The effects of elevated temperature (3-4°C) and CO2 concentration (700 ppm) as expected for Finland in 2100 were simulated. The model was calibrated for long-day growing conditions in Finland. The CERES-wheat genetic coefficients for cv. Polkka were calibrated by using the MTT Agrifood Research Finland (MTT) official variety trial data (1985-1990). Crop phenological development and yield measurements from open-top chamber experiments with ambient and elevated temperature and CO2 treatments were used to validate the model. Simulated mean grain yield under ambient temperature and CO2 conditions was 6.16 t ha-1 for potential growth (4.49 t ha-1 non-potential) and 5.47 t ha-1 for the observed average yield (1992-1994) in ambient open-top chamber conditions. The simulated potential grain yield increased under elevated CO2 (700 ppm) to 142% (167% non-potential) from the simulated reference yield (100%, ambient temperature and CO2 350 ppm). Simulations for current sowing date and elevated temperature (3°C) indicate accelerated anthesis and full maturity. According to the model estimations, potential yield decreased on average to 80.4% (76.8% non-potential) due to temperature increase from the simulated reference. When modelling the concurrent elevated temperature and CO2 interaction, the increase in grain yield due to elevated CO2 was reduced by the elevated temperature. The combined CO2 and temperature effect increased the grain yield to 106% for potential growth (122% non-potential) compared to the reference. Simulating the effects of earlier sowing, the potential grain yield increased under elevated temperature and CO2 conditions to 178% (15 days earlier sowing from 15 May, 700 ppm CO2, 3°C) from the reference. Simulation results suggest that earlier sowing will substantially increase grain yields under elevated CO2 growing conditions with genotypes currently cultivated in Finland, and will mitigate the decrease due to elevated temperature. A longer growing period due to climate change will potentially enable cultivation of new cultivars adapted to a longer growing period. Finally, adaptation strategies for the crop production under elevated temperature and CO2 growing conditions are presented.;
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