PARENT SESSION
Contributed Oral Session 154: Photosynthesis and Water Relations: Climate Effects
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 515 A, Level 5, Palais des congrès de Montréal

Radiation use efficiency of soybean grown in elevated [CO₂] and [O₃].

Dermody, Orla ^*,1, Brewer, Elizabeth ², McConnaughy, Kelly ², Long, Stephen¹, Morgan, Patrick ³, DeLucia, Evan¹, ¹ University of Illinois, Urbana, IL² Bradley University, Peoria, IL³ USDA-ARS Plant Science Research Unit, Raleigh, NC

ABSTRACT- Radiation use efficiency () is a measure of the conversion efficiency of photosynthetically active radiation (PAR) into biomass. Elevated [CO₂] increases leaf area index (LAI) and biomass of soybeans and thus may increase , however, elevated [O₃] may have the opposite effect. These predictions were tested using Soybean Free-Air Concentration Enrichment technology (SoyFACE) with plots (25–m diameter) exposed to ambient air (370ppm), elevated [CO₂] (550ppm) and elevated [O₃] (1.2×ambient), in a fully factorial design. Aboveground crop biomass, LAI and PAR were measured and used to calculate up to the time of maximum LAI. Elevated [CO₂] increased in soybeans by approximately 16%, except in 2003, when the entire crop was damaged by a hailstorm. There was a trend of lower with elevated [O₃]. However, when [CO₂] and [O₃] were elevated in combination, [CO₂] increased by approximately 15% relative to ambient air. Increased in elevated [CO₂] and [CO₂*O₃] co-occurred with increases in maximum LAI, however the effects of [CO₂] on biomass were not significant until maximum LAI and afterwards. Elevated [O₃] had no detectable effect on LAI or biomass before maximum LAI, except in 2003. Knowing that elevated [CO₂] improves soybean will be important in predicting how the productivity of this crop responds to future atmospheric change, however the response of crop to elevated [O₃] remains uncertain.

Key words: SoyFACE, radiation, LAI