Monday, November 13, 2006
61-13
Interactive Effects of Atmospheric Carbon Dioxide and Ozone on Gas-Exchange, Biomass, and Yield of Essex Soybean: A Compilation of Studies from Ten Growing Seasons.
Fitzgerald Booker and Edwin Fiscus. USDA-ARS Plant Science Research Unit, 3908 Inwood Road, Raleigh, NC 27603
Current levels of pollutant O3 in industrialized and developing regions worldwide suppress the growth and yield of many agronomically important crops. Meanwhile, atmospheric concentrations of CO2 continue to increase, due in large part to the same activities leading to elevated tropospheric O3 levels, combustion of fossil fuels. Elevated CO2 is an aerial fertilizer for many crop species, and its metabolic and physiological effects have the potential to lessen O3-induced stress. To investigate interactive effects of these gases on the physiology and productivity of soybean [Glycine max (L.) Merr., cv. Essex], plants were treated with reciprocal combinations of elevated O3 and CO2 over ten growing seasons using open-top field chambers. Results showed that detrimental effects of O3 on net photosynthesis, biomass, and yield were usually attenuated by elevated CO2. Ozone added at 1.5 x ambient levels suppressed net photosynthesis by 18%, and lowered biomass and yield by about 30%, but these effects were almost entirely reversed as CO2 concentrations were increased to twice-ambient levels. In the combined twice-ambient CO2-added O3 treatment, net photosynthesis, biomass, and yield were 22, 24, and 8% higher, respectively, than in the clean air-ambient CO2 control. Twice-ambient CO2 also reduced seasonal average leaf conductance and O3 uptake by about 36%. Lower O3 flux and higher net photosynthesis rates at elevated CO2 were the clearest mechanistic explanations for decreased O3 injury. Additional effects of elevated CO2 on antioxidant capacity, leaf morphology, and as yet, undetermined factors, possibly aided in countering O3 toxicity as well. It is anticipated that increasing atmospheric CO2 concentrations will diminish detrimental effects of ambient O3 and promote growth of soybean but its effectiveness declines with increasing O3 concentrations.
Handout (.pdf format, 87.0 kb)