EFFECTS OF ELEVATED CO2 ON DEVELOPMENT AND MORPHOLOGY OF SPRING WHEATGROWN IN COOLED AND NON-COOLED OPEN-TOP CHAMBERS

Facilities for studying effects of elevated CO2 on crops affect the mi croclimate in the crop. Open-top chambers may increase temperature by 1-3 degrees C compared to ambient conditions. This paper describes a n ewly developed cooling system for open-top chambers. In 1995 and 1996, experiments were carried out to test the system and analyse the effec ts of temperature on crop phenological and morphological response to e levated CO2. Spring wheat (Triticum aestivum L. cv. Minaret) was subje cted to ambient and doubled CO2 concentration in both cooled and non-c ooled chambers. The cooling system reduced temperature by 1.6-2.4 degr ees C, and this delayed maturity by 10 days. In contrast, elevated CO2 did not affect phenological development. Elevated CO2 reduced tiller density, green leaf number per tiller and specific leaf area, thereby reducing the capacity for light interception of the crop. Crop height growth before anthesis mainly responded to temperature, but after anth esis it was only affected by CO2, indicating a shift from sink- to sou rce-limited growth. For none of the parameters studied, a significant statistical interaction of CO2 and temperature was found. The cooling system proved effective. A temperature difference of about 2 degrees C affected crop development and morphology more strongly than CO2 doubl ing. However, the absence of CO2-temperature interaction suggests that CO2 effects may validly be investigated even without a cooling system .