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Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/17/2002 Publication Date: 8/5/2002 Citation: Bunce, J.A. 2002. Carbon dioxide concentration ai night affects translocation from soybean leaves. Annals Of Botany. 90:399-403. Interpretive Summary: Plants lose a substantial part of the carbon they gain through photosynthesis by respiration at night. Controversial evidence suggests that rates of plant respiration may change with the carbon dioxide concentration of the atmosphere. Whether this occurs would have a large impact on the ability of plants to sequester carbon as atmospheric carbon dioxide rises and affect the global carbon balance as well as crop growth rates. The present experiments tested whether translocation, a major consumer of energy from respiration, was sensitive to carbon dioxide. Soybean plants were exposed to three nights with concentrations of 220 to 1400 ppm, with a daytime concentration of 350 ppm. Change in dry mass of the individual leaves over the three day period was determined, along with rates of respiration and photosynthesis, allowing calculation of translocation rates. Results indicated that low carbon dioxide at night increased both respiration and translocation and elevated carbon dioxide decreased both processes. The response of translocation was localized in individual leaves. The results indicated that effects of carbon dioxide concentration on net carbon dioxide exchange rate in the dark had an impact on a physiologically important process which is known to depend on energy supplied by respiration. Thus it is unlikely that the observed effects of carbon dioxide on respiration were artifacts of the measurement process in this case. These results will be important to scientists predicting the impact of rising atmospheric carbon dioxide on global carbon balance, as well as on crop growth. Technical Abstract: Studies have indicated that the concentration of carbon dioxide during the dark period may influence plant dry matter production. It is often suggested that these effects on growth result from effects of carbon dioxide on rates of respiration, but responses of respiration to carbon dioxide remain controversial. The present experiments tested whether translocation, a major consumer of energy from respiration, was sensitive to carbon dioxide. Nineteen day-old soybean plants grown initially at constant 350 ppm carbon dioxide were exposed to three nights with concentrations of 220 to 1400 ppm, with a daytime concentration of 350 ppm. Change in dry mass of the individual second through fourth trifoliate leaves over the three day period was determined, along with rates of respiration and photosynthesis. Translocation was determined from mass balance. Results indicated that low carbon dioxide at night increased both respiration and translocation and elevated carbon dioxide decreased both processes. The effect of carbon dioxide during the dark on the change in leaf mass over 3 days was largest in second leaves, where the change in mass was about 50% higher at 1400 ppm than at 220 ppm. The response of translocation was localized in individual leaves. The results indicated that effects of carbon dioxide concentration on net carbon dioxide exchange rate in the dark had an impact on a physiologically important process which is known to depend on energy supplied by respiration. Thus it is unlikely that the observed effects of carbon dioxide on respiration were artifacts of the measurement process in this case. |
