The impact of ozone exposure, temperature and CO2 on the growth and yield of three spring wheat varieties

When assessing potentials for crop production under future climatic conditions, multiple environmental parameters need to be included. An increase in carbon dioxide [CO2], higher temperatures, and regional changes in tropospheric ozone [O-3] will influence the growth responses of existing crop species and varieties. Ozone is phytotoxic and a plant stressor at current concentrations, reducing yields worldwide, but possible interactions with changes in other abiotic factors have been considered very little. In this study, we have used eight combinations: two levels of temperature, two levels of [CO2], and three [O-3] exposure regimes to assess the impact of medium-to-high ozone concentrations (80-100 ppb) on wheat growth when other abiotic factors change. Two modern spring wheat varieties (KWS Bittern and Lennox) and a landrace variety (Lantvete) were grown to maturity in climate chambers. We examined plant performance during growth as development rate, rate of photosynthesis, stomatal conductance, water use, and at harvest as total aboveground dry matter and grain yield. All three varieties lost yield in all treatments compared to the ambient treatment that had the following settings: Lowest temperature, ambient [CO2], and very low [O-3]. For episodic ozone exposure in the ambient or high [CO2] and high-level temperature treatment, the yield losses were 18 and 25%, respectively, for KWS Bittern; 44 and 34% for Lennox; and 16 and 37% for Lantvete. The yields of the modern varieties are significantly higher than the landrace variety in two out of eight treatments, although they are higher by weight in seven of the eight treatments. The landrace variety's fraction loss from its highest grain yield in the ambient treatment to the high-[CO2]-and high-level-temperature-treatments was smaller than the modern varieties', showing a comparably higher degree of plasticity of performance. Current crop varieties might be more sensitive to ozone than older varieties, emphasizing the need of future breeding programs to expand the gene pool to provide more climate robust crops.