Interactive effects of elevated ozone and carbon dioxide on physiological traits of different Indian mustards

A free air concentration enrichment experiment of different mustard varieties was conducted under elevated (e) ozone (eO3), carbon dioxide (eCO2), a mixture of eO3 x eCO2, and ambient air concentration. The study was conducted to investigate the relationship between plant physiological parameters and changes in atmospheric concentration of O3 and CO2 that may occur under future climates, and to quantify treatment effects on mustard genotypes. Data analysis involved multivariate analysis and the use of linear models that enabled the selection of O3-tolerant and better-performing genotypes under likely future CO2 levels. Plant physiological parameters (namely: total chlorophyll content, leaf area index, antioxidant enzymes and the gas exchange parameters Pn, gs, E, WUE and Tc), and their inter-relationships were measured and recorded at different phenological stages of the crop. All treatments had significant effects on the measured physiological parameters, but differences varied depending upon the physiological stage of the mustard varieties used in the study. The multivariate analysis indicated a strong relationship between measured variables, treatments, and genotypes. Among the three mustard genotypes, 'Pusa Bold' (PB) performed better, followed by PM30, particularly under eO3, and PDZM31 was rather sensitive to increased ozone concentration compared with PB and PM30. The results highlighted that all measured physiological parameters were highly sensitive to changes in the relative concentrations of O3, CO2 and their interaction; particularly, the rate of gas exchange between the plant and the atmosphere. Consequently, crop growth and development were affected. The negative effect eO3 was mitigated the presence of eCO2 as shown in the eO3 x eCO2 treatment.