The Effect of Increased Ozone Levels on the Stable Carbon and Nitrogen Isotopic Signature of Wheat Cultivars and Landraces

Several studies have highlighted the negative effects of ozone (O-3) on wheat development and productivity. The negative effects of O-3 are mediated by changes in photosynthetic carbon and nitrogen metabolism, which are difficult and time-consuming to assess and are thus only measured sporadically throughout the plant cycle. Stable isotope measurements in grains can help integrate the effects of chronic O-3 exposure over the lifespan of the plant. This particular study focuses on the extent to which the stomatal conductance and productivity of Mediterranean wheat are related to carbon and nitrogen isotopic signatures under chronic O-3 exposure. An open top chamber experiment was designed to analyse the effects of the pollutant on 12 Spanish wheat genotypes, which included modern cultivars, old cultivars and landraces. Four O-3 treatments were considered. Stomatal conductance (g(s)) measurements were carried out during anthesis, and yield and nitrogen content parameters were taken at maturity, along with the carbon (delta C-13) and nitrogen (delta N-15) isotopic composition measured in grains. Modern and old cultivars responded similarly to O-3 and were sensitive to the pollutant regarding yield parameters and g(s), while landraces were more O-3-tolerant. Grain delta C-13 had a strong negative correlation with grain yield and stomatal conductance across genotypes and O-3 conditions, and increased under higher O-3 concentrations, showing its capacity to integrate O-3 stress throughout the wheat cycle. Meanwhile, a higher nitrogen concentration in grains, coupled with smaller grains, led to an overall decreased grain nitrogen yield under higher O-3 concentrations. This nitrogen concentration effect within the grain differed among genotypes bred at different ages, following their respective O-3-sensitivity. delta N-15 showed a possible indirect effect of O-3 on nitrogen redistribution, particularly under the highest O-3 concentration. The correlations of delta N-15 and delta C-13 to the usual effects of ozone on the plant suggest their potential as indicators of chronic ozone exposure.

Automated summary

Several studies have demonstrated the negative impacts of ozone on wheat development and productivity, particularly through changes in photosynthetic carbon and nitrogen metabolism. This study focused on the relationship between stomatal conductance, productivity, and carbon and nitrogen isotopic signatures in Mediterranean wheat under chronic O-3 exposure. The results showed that modern and old wheat cultivars were sensitive to O-3, while landraces exhibited more tolerance to the pollutant. Grains with higher delta C-13 values were negatively correlated with yield and stomatal conductance, and nitrogen concentration in grains decreased under higher O-3 concentrations. The delta N-15 values showed a potential indirect effect of O-3 on nitrogen redistribution. These isotopic signatures could serve as indicators of chronic ozone exposure.