PARENT SESSION
Poster Session 24: Agro-Ecology
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Physiological and Growth Responses of Soybeans to Nighttime Carbon Dioxide Enrichment.

Lee, Richard^*,1, Wych, Joseph^*,1, McConnaughay, Kelly, Morris, Sherri, ¹ Bradley University, Peoria, IL, United States

ABSTRACT- Atmospheric CO₂ concentrations ([CO₂]) have been rising due to human activities since the pre-industrial age and are predicted to rise from current concentrations of 360 umol/mol to 723 umol/mol by the end of the 21^st century. Several multi-million dollar, large-scale studies are being conducted to examine the effects of elevated [CO₂] on intact ecosystems. However, many of these free air carbon dioxide enrichment (FACE) sites limit elevated [CO₂] to daytime hours in order to limit costs. Recently, a handful of studies report significant differences in plant growth responses to elevated [CO₂] at night. Our research evaluates, for two cultivars of soybean, Glycine max (L.) Merr. cv. Fiskeby and cv. Clark, whether or not elevated nighttime [CO₂] has a significant effect on plant growth and biomass allocation. The experiment was performed as a growth chamber study with the following treatments: 400 umol mol^-1 [CO₂] for daytime and nighttime, 800 umol mol^-1 [CO₂] for daytime and nighttime, and 800 umol mol^-1 [CO₂] for daytime and 400 umol mol^-1 [CO₂] for nighttime. As expected, elevated daytime [CO₂] resulted in significant increases in growth parameters for both cultivars. Elevated nighttime [CO₂] resulted in significant decreases in several growth parameters for one of the two cultivars of soybean. We are currently investigating whether nighttime [CO₂] alters key leaf-level physiological parameters, including nighttime stomatal conductance. A preliminary evaluation of diurnal patterns of stomatal conductance shows that soybean exhibit appreciable nighttime conductance at approximately 25% of daytime conductance. Overall, our data suggest that plants may be sensitive to differences in nighttime [CO₂], in particular showing decreased growth responses to elevated nighttime [CO₂]. Although uncertainties exist, the implications of our data are that studies ignoring differences in nighttime [CO₂] may be overestimating growth responses to rising atmospheric [CO₂].

Key words: Elevated Nighttime [CO₂], Glycine max, Stomatal conductance, Soybeans