EFFECTS OF ELEVATED CO2 CONCENTRATION AND INCREASED TEMPERATURE ON WINTER-WHEAT - TEST OF ARCWHEAT1 SIMULATION-MODEL

Winter wheat (Triticum aestivum L., cv, Mercia) was grown in a control led-environment facility at two CO2 concentrations (targets 350 and 70 0 mu mol mol(-1)), and two temperature regimes (tracking ambient and a mbient + 4 degrees C), Observations of phenology, canopy growth, dry m atter production and grain yield were used to test the ARCWHEAT1 simul ation model, Dry-matter production and grain yield were increased at e levated CO2 concentration (27 and 39%, respectively) and reduced at in creased temperature (-16 and -35%, respectively), ARCWHEAT1 substantia lly underestimated canopy growth for all treatments, However, differen ces in the facility environment from field conditions over the winter, indicated by the unusually rapid canopy growth observed in this perio d, meant that empirical model relationships were being used outside th e conditions for which they were developed, The ARCWHEAT1 productivity submodel, given observed green area indices as inputs, overestimated the effect of CO2 on productivity, An alternative, more mechanistic su bmodel of productivity, based on the SUCROS87 and Farquhar and von Cae mmerer models, simulated observed crop biomass very closely, When thes e productivity simulations were inputed into the ARCWHEAT1 partitionin g and grain-fill submodels, grain yield was predicted poorly, mainly a s a result of the assumption that the number of grains is proportional to total growth during a short preanthesis phase, While yield was not correlated with growth in this phase, it was correlated with growth i n longer preanthesis phases, indicating that ARCWHEAT1 could be improv ed by taking into account the contribution of earlier growth in determ ining yield.