TEMPERATURE-GRADIENT CHAMBERS FOR RESEARCH ON GLOBAL ENVIRONMENT CHANGE .2. A TWIN-WALL TUNNEL SYSTEM FOR LOW-STATURE, FIELD-GROWN CROPS USING A SPLIT HEAT-PUMP

A temperature gradient chamber (TGC) is described which enables elevated CO2 concentrations and a dynamic temperature gradient to be imposed on field crops throughout their life cycle under standard husbandry. Air is circulated through two double-walled polyethylene-covered tunnels connected to a split heat pump system to give a near-linear temperature gradient along each tunnel, Solar energy gain along each tunnel and exchange with outer tunnel air flow contribute to the temperature gradient and also produce diurnal and seasonal temperature fluctuations corresponding to ambient conditions, Mean temperature gradients of between 3 and 5 degrees C have been recorded throughout the growing seasons of crops of lettuce, carrot, cauliflower and winter wheat, Elevated or present CO2 concentrations are maintained in each of two pairs of tunnels throughout the cropping season using pure CO2 injected through motorized needle valves. This system can realistically simulate aspects of the effects of projected future environmental change on crop growth, development and yield, and in particular the possible interaction of the effects of increased CO2 and temperature.