TEMPERATURE, CO2 AND THE GROWTH AND DEVELOPMENT OF WHEAT - CHANGES INTHE MEAN AND VARIABILITY OF GROWING CONDITIONS

The experiment described here resulted from simulation analyses of cli mate-change studies that highlighted the relative importance of change s in the mean and variance of climatic conditions in the prediction of crop development and yield. Growth and physiological responses of fou r old cultivars of winter wheat, to three temperature and two carbon d ioxide (CO2) regimes (350 or 700 ppmv) were studied in controlled envi ronment chambers. Experimental results supported the previous simulati on analyses. For plants experiencing a 3 degrees C increase in day and night temperatures, relative to local long-term mean temperatures (co ntrol treatment), anthesis and the end of grain filling were advanced, and grain and dry matter yields were reduced by 27% and 18%, respecti vely. Increasing the diurnal temperature range, but maintaining the sa me mean temperature as the control, reduced the maximum leaf area (27% ) and grain yield (13%) but did not affect plant development. Differen ces among the temperature treatments in both phyllochron interval and anthesis date may have resulted from differences between measured air, and unmeasured plant, temperatures, caused by evaporative cooling of the plants. Thermal time (base=0 degrees C), calculated from air tempe rature, from anthesis to the end of grain filling was about 650 degree s C d for all cultivars and treatments. Doubling ambient CO2 concentra tion to 700 ppmv reduced maximum leaf area (21%) but did not influence plant development or tiller numbers.