EFFECTS OF CO2, TEMPERATURE AND THEIR INTERACTION ON THE GROWTH, DEVELOPMENT AND YIELD OF CAULIFLOWER (BRASSICA-OLERACEA L BOTRYTIS)

Stands of summer cauliflower were grown within polyethylene-covered tunnels along which a temperature gradient was imposed. Two tunnels were maintained at either normal or elevated CO2 concentrations. At the last harvest (88 days from transplanting) no interaction between CO2 and temperature on total biomass was detected. The total dry weight of plants grown at 531 mu mol mol-L CO2 was 34% greater than those grown at 328 mu mol mol(-1) CO2, whereas a 1 degrees C rise reduced dry weight by 6%. From serial harvests the radiation conversion coefficient was 2.01 g MJ(-1) and 1.42 g MJ(-1) at 531 mu mol mol(-1) CO2 and 328 mu mol mol(-1) CO2, respectively, but was not greatly affected by differences in temperature. No effect of either CO2 or temperature on the canopy light extinction coefficient was detected. The rate of progress towards curd initiation increased to a maximum at 15.5 degrees C, and declined thereafter. Provided the effect of temperature was accounted for, CO2 enrichment did not affect the time of curd initiation. From serial harvests after curd initiation, the logarithm of curd weight or diameter were negative linear functions of mean temperature from initiation. Increases in curd weight and diameter at 531 compared with 328 mu mol mol(-1) CO2 were greater at warmer temperatures (27% at 13 degrees C compared with 47% at 15 degrees C, 57 days after initiation). Effects of CO2 on curd diameter were less than those on curd dry weight because the curd dry matter content was greater at 531 compared with 328 mu mol mol(-1) CO2. Thus, the effects of elevated CO2 concentrations on fresh weight based yield parameters of cauliflower were less than the increase in total dry matter production.