Rising ozone concentrations decrease soybean evapotranspiration and water use efficiency whilst increasing canopy temperature

Here, we investigated the effects of increasing concentrations of ozone ([O ₃]) 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 (R _n), sensible heat flux (H), soil heat flux (G ₀) and latent heat flux (λET) of a commercial soybean (Glycine max) cultivar (Pioneer 93B15), exposed to a gradient of eight daytime average ozone concentrations ranging from approximately current (c. 40ppb) to three times current (c. 120ppb) levels. • As [O ₃] increased, soybean canopy fluxes of λET decreased and H increased, whereas R _n and G ₀ were not altered significantly. Exposure to increased [O ₃] also resulted in warmer canopies, especially during the day. The lower λET decreased season total evapotranspiration (ET) by c. 26%. The [O ₃]-induced relative decline in ET was half that of the relative decline in seed yield, driving a 50% reduction in seasonal WUE. • These results suggest that rising [O ₃] will alter the canopy energy fluxes that drive regional climate and hydrology, and have a negative impact on productivity and WUE, key ecosystem services.