Title: No minimum threshold for ozone-induced changes in soybean canopy fluxes Authors
Submitted to: Plant Biology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: May 31, 2011
Publication Date: August 6, 2011
Citation: Vanloocke, A., Bernacchi, C.J., Ainsworth, E.A., Betzelberger, A.M. 2011. No minimum threshold for ozone-induced changes in soybean canopy fluxes. [abstract]. American Society of Plant Biologists. Paper No. P06007. Technical Abstract: Tropospheric ozone concentrations [O3] are increasing at rates that exceed any other pollutant. This highly reactive gas drives reductions in plant productivity and canopy water use while also increasing canopy temperature and sensible heat flux. It is not clear whether a minimum threshold of ozone exposure is needed to induce these responses. To investigate whether a minimum threshold exists and what the [O3] are at that threshold, we grew soybean using typical agronomic practices at varying [O3] ranging from 40 to 120 ppb. Yield data were collected and canopy evapotranspiration (ET) and sensible heat flux (H) were measured using a residual canopy energy balance approach. Yield ranged from 4135 kg/ha to 1459 kg/ha and growing season total ET ranged from 406 mm to 298 mm in the control and maximum [O3] respectively. Water-use-efficiency (WUE; i.e. Yield/ET) ranged from 10.5 (kg/ha)/mm the control to 4.9 (kg/ha)/mm in the highest [O3]. H ranged from 30 W/m2 in the control to 51 W/m2 in the maximum [O3] where canopy temperatures were 1.0 deg C warmer than the control. Each canopy scale measurement followed a linear relationship with [O3] with no minimum threshold and did not asymptote at the maximum [O3]. These results indicate that significant changes will occur to the surface energy balance and WUE will decrease in soybean as [O3] increases beyond current concentrations. Because soybean is one of two species that makes up the largest continuous ecosystem in temperate North America, changes in these key ecosystem energy components could result in significant implications for regional climate and water resources.