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Title: Photosynthetic Losses and Peroxidase Induction in Field-grown Soybean in Elevated Ground-level Ozone

item Booker, Fitzgerald
item Burkey, Kent

Submitted to: American Society of Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/14/2006
Publication Date: 10/10/2006
Citation: Morgan, P.B., Booker, F.L., Bernacchi, C.J., Burkey, K.O., Jones, A.M., Long, S.P. 2006. Photosynthetic Losses and Peroxidase Induction in Field-grown Soybean in Elevated Ground-level Ozone. American Society of Agronomy Abstracts.

Interpretive Summary: N/A

Technical Abstract: In industrialized countries of the northern hemisphere, ozone concentrations [O3]have risen by 0.5-2.5% per year, more rapidly than carbon dioxide [CO2]. Nearly 25% of the earth's surface is currently at risk from ground-level ozone in excess of 60 ppb. The US soybean-corn agricultural system covers approximately 62 million hectares making it arguably one of the largest ecosytems. Utilizing SoyFACE (SOYbean Free Atmosphere gas Concentration Enrichment)to elevate [O3] (1.2x ambient) provided a unique opportunity to analyze the ozone-impact in the field. In 2002 & 2003, simultaneous measurements of chlorophyll fluorescence and photosynthetic gas-exchange were made on two groups of excised leaves: the newest topmost fully-expanded leaves and two leaf cohorts over their lifetimes. Total peroxidase activity (measurement of H2O2 detoxification capacity) was made for mature leaves in 2006. Elevated [O3] accelerated leaf senescence hastening losses in carboxylation efficiency (an in vivo measure of Rubisco activity) and photosynthetic electron transport for regeneration of ribulose 1,5-bisphosphate (RuBP. Lost leaf photosynthetic capacity due to elevated [O3] decreased harvest yield by 20%. Following only two, 8-hour fumigations with low-level [O3] in chambers, total peroxidase activity increased in wild-type Arabidopsis leaves. Field-grown soybean also increased total peroxidase activity upon exposure to ozone compared to ozone-free environments. Peroxidase activity increased over the growing season; however, elevated ozone did not further increase leaf peroxidase activity compared to ambient concentrations. These findings emphasize the need to discover how plants respond mechanistically to elevated [o3] at the leaf level as a means of protecting against damage both today and for the future. With the increasing dependence placed upon model projections of crop production, assessing the impacts of ground-level [O3] on crops in the field is crucial to understanding future food production.