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Title:   Author  item
                                            GRAY, S - University Of Illinoisitem
                                            MCGRATH, J - University Of Illinoisitem
                                            DERMODY, O - University Of Illinoisitem
                                            Ainsworth, Elizabeth

                                                         - *Lisa*item
                                            LEAKEY, ANDREW D B - University Of Illinois
  Submitted to: Plant Biology Annual Meeting
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 3/19/2009
                                    Publication  Date: 7/18/2009
                                    Citation: Gray, S.B., McGrath, J.M., Dermody, O., Ainsworth, E.A., Leakey, A. 2009. Temperature and Precipitation Interactions Eliminate Benefits of Free-air CO2 Enrichment to Soybean Water Relations in Two Out of Five Years. Plant Biology Annual Meeting. Plant Biology 2009, July 18-22, 2009, Honolulu, HI.Interpretive Summary:
                                Technical Abstract: A key assumption in projections of future food supply and ecosystem function is that elevated [CO2], through reduced stomatal conductance (gs), results in lower water use, conservation of soil moisture and amelioration of losses in productivity due to drought stress. A 5-year dataset from the soybean Free Air CO2 Enrichment (soyFACE) facility in the Midwest U.S. demonstrates that soybean did not benefit from this mechanism in 2 out of 5 years. Interannual variability in the effects of elevated [CO2] (550 ppm) on photosynthesis (A) and leaf area index (LAI) drives this variation in soil moisture and this interannual variability was a function of precipitation and temperature. Soil moisture in elevated [CO2] was greater in 2004 (up to 60%), 2005 (up to 20%), and 2007(up to 25%). On average, this was associated with a ~27% reduction in midday gs, a ~21% stimulation in midday A, and a ~5% stimulation in peak LAI in elevated [CO2]. In 2006 and 2008 however, elevated [CO2] did not significantly affect soil moisture, despite reducing gs~25%. In 2006, high rainfall throughout the season resulted in soil moisture at or near field capacity, eliminating any benefits of decreased gs in elevated [CO2]. In 2008, an unusually wet spring delayed planting by one month, resulting in soybeans developing under higher temperatures than usual. This late planting and higher temperatures amplified the stimulation of LAI by elevated [CO2], offsetting reductions in gs and eliminating any improvement in soil moisture at elevated [CO2]. Consequently, during a drought in August, there was no stimulation of A at elevated [CO2]. This suggests that increasing temperature and drought will diminish the benefits of elevated [CO2] to plant productivity in the future more than currently predicted.


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