Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2012
Publication Date: July 1, 2012
Citation: VanLoocke, A., Betzelberger, A.M., Ainsworth, E.A., Bernacchi, C.J. 2012. Rising ozone concentrations decrease soybean evapotranspiration and water use efficiency while increasing canopy temperature. New Phytologist. 195(1):164-171. Interpretive Summary: The concentration of ground-level ozone ([O3]) has approximately doubled since the start of the industrial revolution and is projected to continue increasing through the 21st century. Ozone is highly reactive and can impose damage to any sensitive biological surfaces with which it comes into contact. Damage for many plant species becomes apparent at concentrations well below levels considered dangerous for human health. Damaging concentrations are commonly experienced by vegetation and as a result there is clear evidence that [O3] is already impacting major food crops. Therefore it is important to understand how increasing [O3] will impact crops. We investigated the effects of increasing [O3] on soybean yields, water use, and water use efficiency (WUE) at the Soybean Free Air Concentration Enrichment (SoyFACE) facility. Micrometeorological measurements were made and the crop was harvested to determine the water use and yield of soybean exposed to a gradient of eight [O3] ranging from current levels to approximately three times current. When comparing the lowest to the highest [O3] our results indicated that water use declined by approximately 26% while yield decreased nearly twice as much. Because yield decreased twice as much as water use, WUE decreased by 50% from lowest to highest [O3]. In addition to these affects, the temperature of the soybean leaves increased by almost 2°C, with the biggest differences occurring around noon. Because the amount of water and heat coming out of the crop impacts atmospheric conditions, the impact of increasing [O3] extends beyond yield reductions to impact climate. Since soybeans cover so much of the Midwestern US, it is possible that increasing [O3] can impact the regional cycling of water as well as the climate.
Technical Abstract: We investigated the effects of increasing [O3] on soybean canopy scale fluxes of heat and water vapor as well as water use efficiency (WUE) at the Soybean Free Air Concentration Enrichment (SoyFACE) facility. Micrometeorological measurements were made to determine the net radiation (Rn) sensible heat flux (H), soil heat flux (G0), and evapotranspiration (ET) of soybean exposed to a gradient of eight ozone concentrations ranging from current levels to ca. three times current. As [O3] increased, soybean canopy fluxes of ET declined and H increased, while Rn and G0 were not significantly altered. Exposure to O3 also resulted in warmer canopies, more so during the day. Over the range of [O3] and throughout the growing season, the total decline in ET was half that of the seed yield, driving a 50% reduction in seasonal WUE.