The response of soybean seedling growth to carbon dioxide concentration at night in different thermal regimes

BUNCE J. A. The response of soybean seedling growth to carbon dioxide concentration at night in different thermal regimes. BIOTRONICS 30, 15-26. 2001. Carbon dioxide concentration during the dark is often not controlled in investigations of plant growth or in studies of plant responses to elevated [C02J in the field. In this work we have investigated whether [C02J at night significantly affected the growth of soybean seedlings, and whether this varied with the magnitude of the day/night temperature variation. Plants were grown under day/night [C02J s of 350/350, 350/700, 700/700 and 700/350,umol mol- 1 [C02J in controlled-environment chambers under four temperature regimes. Field studies were also conducted, using semi-open chambers in which plants were fumigated with air at the ambient [C02J or with air at ambient +350,umol mol~l [C02J applied only during the day, only at night, or for 24 h per day. When the day [C02J was low, elevated [C02J at night decreased plant leaf area and dry mass with constant day/night temperatures, but had no effect when there was a diurnal change in temperature. With hig