Differential root responses in two cultivars of winter wheat (Triticum aestivum L.) to elevated ozone concentration under fully open-air field conditions

The effect of elevated tropospheric ozone concentration [O-3] on root processes in wheat systems of different O-3 sensitivity is not well understood. Two wheat cultivars (cv. Y15 and YN19) with contrasting O-3 tolerance were grown in a fully open-air O-3 enrichment platform for one season. We found that elevated O-3 (EO3) (50% above the ambient O-3) significantly decreased the total biomass at all key growth stages and the yield of the O-3-sensitive cultivar YN19 but did not affect those of the O-3-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 O-3-tolerant cultivars to maintain crop yield under higher [O-3] scenarios.