THE EFFECTS OF CO2, TEMPERATURE AND THEIR INTERACTION ON THE GROWTH AND YIELD OF CARROT (DAUCUS-CAROTA L)

Stands of carrot (Daucus carota L.) were grown in the field within pol yethylene-covered tunnels at a range of soil temperatures (from a mean of 7.5 degrees C to 10.9 degrees C) at either 348 (SE = 4.7) or 551 ( SE = 7.7) mu mol mol(-1) CO2. The effect of increased atmospheric CO2 concentration on root yield was greater than that on total biomass, At the last harvest (137 d from sowing), total biomass was 16% (95% CI=6 %, 27%) greater at 551 than at 348 mu mol mol(-1) CO2, and 37% (95% CI =30%, 44%) greater as a result of a 1 degrees C rise In soil temperatu re, Enrichment with CO2, or a 1 degrees C rise in soil temperature inc reased root yield by 31% (95% CI=19%, 45%) and 34% (95% CI=27%, 42%), respectively, at this harvest, No effect on total biomass or root yiel d of an interaction between temperature and atmospheric CO2 concentrat ion at 137 DAS was detected, When compared at a given leaf number (sev en leaves), CO2 enrichment increased total biomass by 25% and root yie lds by 80%, but no effect of differences in temperature on plant weigh ts was found, Thus, increases in total biomass and root yield observed in the warmer crops were a result of the effects of temperature on th e timing of crop growth and development, Partitioning to the storage r oots during early root expansion was greater at 551 than at 348 mu mol mol(-1) CO2. The root to total weight ratio was unaffected by differe nces in temperature at 551 mu mol mol(-1) CO2, but was reduced by cool er temperatures at 348 mu mol mol(-1) CO2. At a given thermal time fro m sowing, CO2 enrichment increased the leaf area per plant, particular ly during early root growth, primarily as a result of an increase in t he rate of leaf area expansion, and not an increase in leaf number.