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item Bunce, James

Submitted to: Biotronics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2001
Publication Date: 9/1/2001
Citation: Bunce, J.A. 2001. The response of soybean seedling growth to carbon dioxide concentration at night in different thermal regimes. Biotronics. 30:15-26.

Interpretive Summary: The concentration of carbon dioxide in the atmosphere is rising rapidly, and may affect the growth of crop plants in ways which are not yet predictable. Studies simulating increased atmospheric carbon dioxide concentration in order to determine crop responses often do not elevate carbon dioxide concentration during the dark period, due to the extra expense, and because it has been assumed that carbon dioxide concentration during the dark period would not affect plants. In this work we investigated whether the concentration of carbon dioxide at night significantly affected the growth of soybean seedlings. Experiments conducted both in controlled environment chambers and in the field indicated significant effects of carbon dioxide concentration at night on the growth rate of soybean seedlings. The exact response to night time carbon dioxide concentration depended on the temperature regime. The results indicate that accurate information on crop responses to rising atmospheric carbon dioxide require the carbon dioxide treatments be applied 24 hours per day. This information will be of use to crop scientists predicting the response of crop plants to the rising atmospheric carbon dioxide concentration.

Technical Abstract: Carbon dioxide (C02) concentration during the dark is not controlled in investigations of plant growth or studies of plant responses to elevated CO2 in the field. We have investigated whether CO2 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 CO2 of 350/350, 350/700, 700/700, and 700/350 ppm CO2 in controlled-environment chambers under four temperature regimes. Field studies were conducted using semi-open chambers in which plants were fumigated with air at the ambient CO2 or with air at ambient + 350 ppm CO2 applied during the day, only at night, or for 24 h's per day. When the day CO2 was low, elevated CO2 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 high CO2 in the day, elevated CO2 at night decreased plant leaf area and dried mass when the diurnal change in temperature was small, but increased these parameters when the diurnal change in temperature was larger. The data for the field was similar to that obtained in the controlled-environment chambers in the regimes with the larger diurnal temperature changes. No effect of elevated CO2 on leaf area or biomass was observed in the field when the elevated CO2 treatment was applied only in the daytime. The results indicate that a build up of CO2 at night in controlled-environment chambers or in the field can significantly reduce plant biomass under some temperature regimes for plants grown at low CO2 in the day time. The results indicate the usefulness of controlling CO2 at night in studies of plant growth.