Phytotoxic effects of tropospheric ozone altered by elevated levels of CO2 in Indian mustard for Sustaining production

Tropospheric ozone is the most important air pollutant of global concern since it affects crops negatively by causing oxidative damage. The increased levels of carbon dioxide positively impacted the C ₃ plants. The impacts of elevated O ₃ and CO ₂ on most crops have been studied, but the information in relation to the interactive effects of O ₃ and CO ₂ is still limited and elusive in Indian mustard. Thus, the study was aimed at quantifying the impacts of elevated O ₃ (Ambient + 25±5 ppb) and CO ₂ (550±10 ppm) along with their interaction on different winter mustard varieties, to elucidate their response towards growth and yield parameters as well as photosynthetic activity and stomatal behaviour for two seasons (2020-21 & 2021-22). The photosynthetic activity in mustard declined by about 16%, crop index by 15% and seed yield by 24% under elevated O ₃ treatments. Contrarily, the CO ₂ enrichment treatments nullified the O ₃ effects on yield by a maximum of 17% in PDZM 31 followed by 14% in Pusa Bold and 13% in PM 30. The elevated levels of ozone reduced stomatal conductance, and the photosynthetic activity offsetted by elevated CO ₂ acts as a defensive mechanism to avoid the entry of O ₃ into leaf tissues and restrict the production of reactive oxygen species. Thus, the current interaction studies revealed that the strong oxidative damage caused by elevated O ₃ was reduced by elevated CO ₂ in mustard varieties and discussed in detail.