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Inhibition of whole plant respiration by elevated CO2 as modified by growth temperature


L. H. Ziska (Corresponding author)


Plants of alfalfa (Medicago sativa) and orchard grass (Dactylus glomerata) were grown in controlled environment chambers at two CO2 concentrations (350 and 700 μmol mol-1) and 4 constant day/night growth temperatures of 15, 20, 25 and 30°C for 50–90 days to determine changes in growth and whole plant CO2 efflux (dark respiration). To facilitate comparisons with other studies, respiration data were expressed on the basis of leaf area, dry weight and protein. Growth at elevated CO2 increased total plant biomass at all temperatures relative to ambient CO2, but the relative enhancement declined (P≤0.05) as temperature increased. Whole plant respiration (Rd) at elevated CO2 declined at 15 and 20°C in D. glomerata on an area, weight or protein basis and in M. sativa on a weight or protein basis when compared to ambient CO2. Separation of Rd into respiration required for growth (Rg) and maintenance (Rm) showed a significant effect of elevated CO2 on both components. Rm was reduced in both species but only at lower temperatures (15°C in M. sativa and 15 and 20°C in D. glomerata). The effect on Rm could not be accounted for by protein content in either species. Rg was also reduced with elevated CO2; however no particular effect of temperature was observed, i. e. Rg was reduced at 20, 25 and 30°C in M. sativa and at 15 and 25°C in D. glomerata. For the two perennial species used in the present study, the data suggest that both Rg and Rm can be reduced by anticipated increases in atmospheric CO2; however, CO2 inhibition of total plant respiration may decline as a function of increasing temperature