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Title: EFFECTS OF SEASON LONG ELEVATION OF [O-3] ON LEAF GROWTH AND PHOTOSYNTHESIS OF SOYBEAN IN THE FIELD

Author
item CHRIST, M - JUELICH RESEARCH CENTER
item Ainsworth, Elizabeth - Lisa
item SCHURR, U - JUELICH RESEARCH CENTER
item WALTER, A - JUELICH RESEARCH CENTER

Submitted to: International Botanical Congress
Publication Type: Abstract Only
Publication Acceptance Date: 7/17/2005
Publication Date: 8/1/2005
Citation: Christ, M.M., Ainsworth, E.A., Schurr, U., Walter, A. 2005. Effects of season long elevation of [O-3] on leaf growth and photosynthesis of soybean in the field [abstract]. XVII International Botanical Congress. Paper No. 2-9-03.

Interpretive Summary: Ozone concentration in the lower atmosphere (troposphere) has risen significantly since 1900 and is predicted to increase throughout this century as well. In the northern hemisphere, high ozone levels usually occur during the warm, sunny summer months, which coincides with crop growing season. We investigated how increased ozone affects soybean carbon uptake and leaf growth. Both photosynthesis (carbon uptake) and individual leaf growth were reduced in plants grown under elevated ozone concentrations. Leaves exposed to high ozone also had lower levels of soluble sugars. Interestingly, final yield was not significantly decreased by ozone. This experiment showed that growth of vegetative organs was decreased while growth of reproductive organs was maintained.

Technical Abstract: Surface ozone concentration ([O-3]) has risen from an estimated pre-industrial value of 10 ppb to an average of ~60 ppb in the middle latitudes of the northern hemisphere, where it is predicted to rise by 20% in the next 50 years. The effects of elevated [O-3] (1.2 x ambient) on soybean (Glycine max cv. Spencer) leaf growth and photosynthesis were investigated under fully open-air conditions at the SoyFACE facility in Urbana-Champaign, IL, USA. The experiments were performed during pod-fill, when detrimental effects of O-3 would have the greatest impact on soybean yield. Photosynthetic carbon uptake was reduced in both growing and mature leaves by ~30% due to lower stomatal conductance. Soluble leaf carbohydrate contents were lower under elevated [O-3]. Starch accumulation was observed in mature leaves, indicating altered sugar transport to sink organs. These changes in photosynthate availability appear to have reduced leaf growth rates, resulting in decreased leaf area at the end of pod-fill. However, the final yield was unaffected by elevated [O-3] suggesting photosynthate was preferentially allocated to reproductive sinks.