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

Abstract

Several studies have highlighted the negative effects of ozone (O3) on wheat development and productivity. The negative effects of O3 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 O3 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 O3 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 O3 treatments were considered. Stomatal conductance (gs) measurements were carried out during anthesis, and yield and nitrogen content parameters were taken at maturity, along with the carbon (δ13C) and nitrogen (δ15N) isotopic composition measured in grains. Modern and old cultivars responded similarly to O3 and were sensitive to the pollutant regarding yield parameters and gs, while landraces were more O3-tolerant. Grain δ13C had a strong negative correlation with grain yield and stomatal conductance across genotypes and O3 conditions, and increased under higher O3 concentrations, showing its capacity to integrate O3 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 O3 concentrations. This nitrogen concentration effect within the grain differed among genotypes bred at different ages, following their respective O3-sensitivity. δ15N showed a possible indirect effect of O3 on nitrogen redistribution, particularly under the highest O3 concentration. The correlations of δ15N and δ13C to the usual effects of ozone on the plant suggest their potential as indicators of chronic ozone exposure.

Crop phenotyping in a context of global change: What to measure and how to do it

“…Interestingly, this conclusion did not agree with results from gas exchange analysis, which further supports the analysis of δ 13 C in grains as a proxy to phenotype the effect of O 3 on crops (Saurer et al, 1991). Recently, Chang‐Espino et al (2021) have also reported a clear effect of O 3 levels in decreasing grain δ 13 C, but this decrease was clearly paralleled by a decrease in stomatal conductance, biomass, and yield. Moreover, the study clearly shows the effectiveness of δ 13 C for phenotyping genotypic susceptibility to O 3 in wheat.…”

“…In addition, to measure carbon (δ 13 C) and nitrogen (δ 15 N) stable isotopes is an alternative way to analyze the effect of ozone and other air pollutants. Indeed, chronic stress caused by air pollutants can increase δ 13 C (or decrease Δ 13 C) by affecting stomatal closure and Rubisco carboxylation (Farquhar et al, 1989a(Farquhar et al, , 1989b, while δ 15 N is related more to nitrogen translocation (Chang-Espino et al, 2021). In fact, δ 13 C has been proposed as a proxy to assess the effect of O 3 on stomatal conductance.…”

“…Furthermore, in the case of major crop species such as wheat, genotypic differences in O 3 tolerance have been observed, where modern varieties are more sensitive than older varieties (Hamens et al, 2018) or even landraces (Chang‐Espino et al, 2021), because the breeding process designed to favor yield has been linked to an increase in photosynthetic activity through higher stomatal conductance (Roche, 2015), which indirectly favors the absorption of gaseous pollutants (Pleijel et al, 2006; Fatima et al, 2019). Therefore, modern varieties show a faster drop in yield under both chronic and acute exposures.…”

Maize Intercropping in the Traditional “Milpa” System. Physiological, Morphological, and Agronomical Parameters under Induced Warming: Evidence of related Effect of Climate Change in San Luis Potosí (Mexico)

“…Open-top chamber (OTC) structures were used to simulate the induced passive heat. These structures allow for passive heating and are a simple method for monitoring plant responses to abiotic variables such as temperature increases in the field [ 16 , 17 , 24 , 25 ]. The finished structures were pentagonal at the surface base, with a perimeter of 10.8 m [(2.5 m × 4) + 0.8 m] and a height of 3 m ( Figure 3 A,B).…”

“…The use of an Open-top chamber (OTC) has been one of the most popular methods for simulating potential plant growth and development. The OTC structure has been used by [ 15 , 16 , 17 , 18 ] to evaluate the effect of abiotic variables on plants. These studies are helpful in developing strategies for mitigating the negative effects of climate change on plant production in small-scale management systems, where food security is severely challenged by climate change [ 19 ].…”