EFFECTS OF CO2 AND TEMPERATURE ON GROWTH AND YIELD OF CROPS OF WINTER-WHEAT OVER 4 SEASONS

Crops of winter wheat (Triticum aestivum L. cv. Hereward) were grown i n the field in four consecutive seasons from 1991/1992 to 1994/1995 at Reading, UK, within polyethylene-covered tunnels along which a temper ature gradient was superimposed on the ambient temperature variation a t normal atmospheric (ca. 370) or an increased [CO2] (ca. 700 mu mol C O2 mol(-1) air), producing many environments from one sowing date in e ach season at one location. Mean seasonal temperatures varied by up to 4 degrees C along the temperature gradient. Increased [CO2] had no ef fect on crop duration, or on the rate of reproductive development, whi ch had the same temperature sensitivity across all years, A 2 degrees C warming, on the 4-year ambient mean temperature (10 degrees C), redu ced crop duration by 42 days (from 254), and reduced the reproductive phase by 16 days (from 130). Crop biomass generally declined with incr ease in mean temperature, and was greater at increased [CO2], with the effect of increased [CO2] varying with temperature and between years (6-34% range in relative stimulation by increased [CO2]). Grain yield was substantially reduced by warmer temperatures, and increased by dou bling [CO2], but the effect varied greatly between pears and with temp erature (7-168% range). There were both positive and negative interact ions of temperature and increased [CO2] on biomass and grain yield. In all 4 years, the increase in grain yield from doubling [CO2] was nega ted by an increase in mean seasonal temperature of only 1.0-2.0 degree s C, Year-to-year variation in the responses of biomass and grain yiel d to [CO2] and temperature resulted from differences in environmental conditions, influencing biomass partitioning and altering the role of different yield components. (C) 1997 Elsevier Science B.V.