The effect of elevated tropospheric ozone concentration [O3] on root processes in wheat systems of different O3 sensitivity is not well understood. Two wheat cultivars (cv. Y15 and YN19) with contrasting O3 tolerance were grown in a fully open‐air O3 enrichment platform for one season. We found that elevated O3 (EO3) (50% above the ambient O3) significantly decreased the total biomass at all key growth stages and the yield of the O3‐sensitive cultivar YN19 but did not affect those of the O3‐tolerant cultivar Y15. EO3 significantly decreased the root biomass of two wheat cultivars at the jointing and grain‐filling stages. EO3 significantly decreased the root length, length density, surface area and volume of the two cultivars at the jointing stage but increased those of YN19 at the grain‐filling stage. EO3 significantly increased the root activities (specific root respiration rates) of Y15 and YN19 at the jointing, heading and grain‐filling stages. EO3 significantly decreased the contribution of fresh root respiration to soil respiration (CRS) of YN19 at the jointing stage but increased it at the heading stage; however, it did not change the CRS of Y15 at any growth stages. This study indicates that the effects of EO3 on root morphology and activity varied among wheat cultivars, and suggest that we can breed O3‐tolerant cultivars to maintain crop yield under higher [O3] scenarios.

Understanding the effects of elevated O3 (EO3) on belowground process such as soil enzyme activities is essential to evaluate plant physiological reaction and soil processes (e.g. carbon and nitrogen turnover) under predicted increases in atmospheric O3. In this study, O3‐induced changes in soil urease (UA) and catalase activities (CTA) under two contrasting wheat cultivars (O3‐sensitive versus O3‐tolerant) were investigated using a free‐air O3 enrichment (O3FACE) facility in China. EO3 (60 ppb compared with 40 ppb in ambient O3) generally increased UA under the O3‐tolerant cultivar but reduced it under the O3‐sensitive cultivar for different soil depths and growth stages. In contrast, the effects of EO3 on CTA were not consistent and varied with soil depths and growth stages. These results suggest that the O3 sensitivity of wheat cultivars plays an important role in determining the effects of EO3 on soil enzyme activities. The contrasting responses of soil UA and CTA to EO3 may alter the effect of projected increase in tropospheric O3 on soil carbon and nitrogen turnover.

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