Submitted to: ASA-CSSA-SSSA Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2003
Publication Date: N/A
Technical Abstract: Fossil fuel combustion is increasing carbon dioxide ([CO2]) and tropospheric ozone concentrations ([O3]). In countries of the northern hemisphere, [O3] have risen by 1-2% per year, more rapidly than [CO2]; a trend predicted to continue under major Intergovernmental Panel on Climate Change scenarios. Nearly 25% of the earth's surface is currently at risk from [O3]in excess of 60 ppb. These changes alter biomass and reproductive production, but are based primarily on controlled environment experiments. The effects of the two gases have not been studied under open-air field conditions. Utilizing SoyFACE (www.soyface.uiuc.edu), a unique facility that elevates [O3](1.2x ambient) and [CO2] (0.550 mmol/mol), provided a unique opportunity to analyze effects of these two gases in the field. Photosynthetic carboxylation efficiency (measure of Rubisco activity) decreased in elevated [CO2], while electron transport to regeneration of RuBP was not affected, suggesting acclimation to elevated [CO2]. Elevated [O3] accelerated leaf senescence and losses in carboxylation efficiency and electron transport. The effects of increased photosynthesis in elevated [CO2] (15%) were reflected in aboveground production and yield (10-15% increases). Decreased photosynthesis due to elevated [O3] decreased yield 20%. Assuming that [O3] rises linearly, our study suggests that rising [O3] will increase annual losses by $21 million/year over the next 30 yrs.