CLIMATE-CHANGE - A RESPONSE-SURFACE STUDY OF THE EFFECTS OF CO2 AND TEMPERATURE ON THE GROWTH OF BEETROOT, CARROTS AND ONIONS

Ten daylit, controlled-environment cabinets were used to investigate t he possible impacts of global rises in atmospheric CO2 concentration a nd temperature on beetroot (Beta vulgaris L.), carrot (Daucus carota L .) and bulb onion (Allium cepa L.) plants. Their responses to CO2 conc entrations of 350, 450, 550, 650 and 750 vpm and temperatures of 12, 1 3.5, 15, 16.5 and 18 degrees C were examined by using a fractional fac torial design for the two treatment factors. Use of the daylit cabinet s allowed the plants to be grown in natural light, common atmospheric humidities (vpd 0.7 kPa) and nonlimiting supplies of water and mineral nutrients. Polynomial models were used to summarize the whole plant d ry weight and fresh weight yield responses and to indicate the potenti al impact of climate change. Additionally, the models were used to gen erate predictions of the percentage change in whole plant dry weight a nd plant fresh weight yield for the years 2025 and 2050 relative to 19 92. Baseline values of 350 vpm for CO2 and a mean temperature of 13.5 degrees C for 1992 together with forecast CO2 values of 407 and 442 vp m and temperature increases of 0.7 and 1.1 C for 2025 and 2050 respect ively were used. For 2025, fresh weight yield changes of + 19%, +9% an d +13% were obtained for beetroot, carrot and onion crops respectively , while for 2050 the respective changes were + 32 %, + 13 % and +21 %. Measurements of the ratio of the maximum diameter of the bulb to the minimum diameter of the neck for onions showed that there was little o r no influence of CO2, whereas the effect of temperature was substanti al. Bulbing was accelerated by high temperature and was greatly delaye d at low temperature. At temperatures < 15 degrees C, the delays to bu lbing resulted in the development of undesirable, thick-necked onions which tended to remain green with erect leaves. These results suggest, therefore, that a warmer climate will be advantageous for the commerc ial production of bulb onions in Britain.