Submitted to: Annals Of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 11, 2000
Publication Date: N/A
Interpretive Summary: Respiration is an important component of plant carbon balance, since plants typically respire away about 30% of the carbon they gain from photosynthesis each day. Increased concentrations of carbon dioxide have frequently been reported to decrease the rate of respiration. This has potentially important implications not only for plant growth at the elevated concentrations of carbon dioxide anticipated for the atmosphere, but also has important implications for the rate of change in atmospheric carbon dioxide concentration. The magnitude of the reduction in respiration rate with increased carbon dioxide is quite variable, and is unusually subject to measurement errors. This work examined the hypothesis that the relative magnitude of the response would be less in tissue depleted of reserve carbohydrates. Additionally, this study made a concerted effort to reduce the known measurement errors. It was found that, opposite to the hypothesis, depleting leaves of carbohydrates by prolonged darkness increased their relative sensitivity to carbon dioxide concentration. Analysis of measurement errors indicated that although measurement errors are large, known errors in measurement cannot account for the response of respiration rate to carbon dioxide concentration. This work will be of interest to scientists examining plant growth responses to increasing atmospheric carbon dioxide and to scientists predicting the rate of change in atmospheric carbon dioxide concentration.
Direct effects of measurement carbon dioxide concentration [CO2] on rates of respiration of plant tissue are quite variable. One possible source of variation in responsiveness is the energy status of the tissue, which could influence the control coefficients of enzymes, such as cytochrome-c oxidase, whose activity is sensitive to [CO2]. In this study, we compared responses of respiration rate to [CO2] over the range of 60 to 1000 ppm in fully expanded leaves of four C3 and four C4 herbaceous species. Responses were measured near the middle of the normal 10h dark period, and also after another 24h of darkness. Rates of respiration were reduced on average about 70% by the prolonged dark period, and leaf dry mass per unit of area was decreased about 30%. In all species, the relative decrease in respiration rate with increasing [CO2] was larger after prolonged darkness. In the C3 species, rates measured at 1000 ppm [CO2] averaged 0.89 of those measured at 60 ppm in the middle of the normal dark period, and 0.70 times when measured after prolonged darkness. In the C4 species, rates measured at 1000 ppm [CO2] averaged 0.79 of those at 60 ppm in the middle of the normal dark period, and 0.51 times when measured after prolonged darkness. In three of the C3 species and one of the C4 species, the decrease in the absolute respiration rate between 60 and 1000 ppm [CO2] was essentially the same in the middle of the normal night period and after prolonged darkness. In the other species, the decrease in the absolute rate of respiration with increase in [CO2] was substantially less after prolonged darkness than in the middle of the normal night period.