Professor Stephen Long, plant scientist at the University of Illinois, Patrick Morgan and Professor German Bollero, both also at the University of Illinois, and Carl Bernacchi of the U.S. Department of Agriculture/Agricultural Research Service conducted this study.
The plant scientists said they expect elevated tropospheric ozone concentration to inhibit photosynthesis in soybean and therefore significantly decrease growth and yield.
Most elevated tropospheric ozone concentration 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 tropospheric ozone concentration (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 tropospheric ozone concentration throughout the crop canopy without altering the microclimate. Simultaneous measurements of fluorescence and gas-exchange (assimilation vs. light and assimilation vs. intercellular carbon dioxide concentration) 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 tropospheric ozone concentration 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 tropospheric ozone concentration 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 tropospheric ozone concentration 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 tropospheric ozone concentration rises linearly, the research team's measured biomass losses suggest that predicted rises in tropospheric ozone concentration over the next 30 years would cost the US soybean industry an additional $21 million each year based on 2002 production, the scientists said.
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, the scientists concluded.
The findings of this research will be presented at the annual meeting of the American Society of Plant Biologists (ASPB) at a minisymposium 8 a.m. to 9:40 a.m. Hawaii Time July 30, 2003 in Honolulu, Hawaii. Each scientist authoring the presentation from the study is a member of ASPB, a non-profit society founded in 1924 representing nearly 6,000 plant scientists.
Presenter: Patrick Morgan, patrickm@life.uiuc.edu
Authors: Patrick Morgan, Department of Plant Biology, University of Illinois; Carl Bernacchi, USDA Agricultural Research Service; German Bollero, Department of Crop Sciences, University of Illinois; Stephen Long, Department of Plant Biology, University of Illinois.