Minisymposium 20: Global Change
Abs #
34003: Altered photosynthesis and biomass production by soybean grown in future O3 concentrations under open-air field conditions
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Presenter: |
Morgan, Patrick B, patrickm@life.uiuc.edu |
Authors | Morgan, Patrick B (A) Bernacchi, Carl J (B) Bollero, German A (C) Long, Stephen P (A) (C) | | Affiliations: |
(A): Department of Plant Biology, University of Illinois
(B): United States Department of Agriculture/Agricultural Research Service
(C): Department of Crop Sciences, University of Illinois
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| Web Site: | http://www.soyface.uiuc.edu | |
Rising atmospheric carbon dioxide concentration ([CO2]) is widely recognized, but less well publicized is the concomitant rise in tropospheric ozone concentration ([O3]). In industrialized countries, [O3] has risen by 0.5-2.5% per year (more rapidly than [CO2]) and is predicted to reach a global mean of 63 parts per billion by 2030, with higher concentrations in the northern hemisphere (UN-IPCC, 2001). We expect elevated [O3] to inhibit photosynthesis in soybean and therefore significantly decrease growth and yield. Most elevated [O3] studies have been conducted in chambers, which drastically alter the microclimate thus limiting extrapolation to field grown plants. SoyFACE (Soybean Free Air Concentration Enrichment, www.soyface.uiuc.edu) is the first facility to elevate atmospheric [O3] (1.21 x ambient, 2030 level) in replicated plots under open-air conditions within an agricultural field. This system utilizes prevailing wind to deliver elevated [O3] throughout the crop canopy without altering the microclimate. Simultaneous measurements of fluorescence and gas-exchange (assimilation vs. light and assimilation vs. intercellular [CO2]) were made on two groups of excised leaves: the newest topmost fully-expanded leaves over the growing season and two leaf cohorts over their lifetimes. In the topmost fully-expanded leaf, growth in elevated [O3] did not alter light-saturated photosynthesis (Asat, p=0.14). Carboxylation capacity of Rubisco (Vcmax) is often limiting under many field conditions. In the topmost leaves, elevated [O3] did not alter Vcmax (p=0.81) or maximum electron transport for ribulose 1,5-bisphosphate regeneration (Jmax, p=0.65) at any developmental stage and did not alter the Vcmax/Jmax ratio. However, as leaves aged, the progressive decrease of Asat was faster in elevated [O3] and both Vcmax and Jmax were significantly decreased. These ozone-induced decreases resulted in a 22% decrease (240 g/m2, p=0.007) in aboveground dry-matter production and a 20% loss (143 g/m2, p=0.022) in reproductive yield. Assuming that [O3] rises linearly, our measured biomass losses suggest that predicted rises in [O3] over the next 30 years would cost the US soybean industry an additional $21 million each year based on 2002 production. Since ozone-induced losses directly result from decreased photosynthesis, these findings emphasize the need to discover means of protecting the photosynthetic apparatus against damage both for the future and today.
