Combating ozone stress through N fertilization: A case study of Indian bean (Dolichos lablab L.)

The present study investigates the efficiency of nitrogen (N) amendments in the management of ozone (O₃) stress in two varieties (Kashi Sheetal and Kashi Harittima) of Indian bean (Dolichos lablab L.). Two O₃ concentrations, ambient (44.9 ppb) and elevated (74.64 ppb) were used, and each O₃ concentration has 3 nitrogen (N) dose treatments viz recommended (N1), 1.5 times recommended (N2), 2 times recommended (N3) and no nitrogen, which served as control (C). The experiment concluded Kashi Sheetal as O₃ tolerant, as compared to Kashi Harittima. N amendments were effective in the partial amelioration of O₃ stress, with N2 being the most effective nitrogen dose, at both ambient and elevated O₃ concentrations. Kashi Sheetal has been determined to be O₃ tolerant due to greater endogenous levels of H₂O₂ accumulation and enzymatic antioxidant contents with O₃ exposure. The O₃-sensitive variety, Kashi Harittima, responded more positively to N treatments, at both O₃ concentrations. The positive effect of N amendments is attributed to the stimulated antioxidative enzyme activity, rather than the biophysical processes like stomatal conductance. Strengthened defense upon N amendments was attributed to the enhanced activities of APX and GR in Kashi Sheetal, while in Kashi Harittima, the two enzymes (APX and GR) were coupled by SOD and CAT as well, during the reproductive phase. Yield (weight of seeds plant^-1) increments upon N (N2) amendments were higher in Kashi Harittima (O₃ sensitive), as compared to Kashi Sheetal (O₃ tolerant) at both ambient and elevated O₃ concentration, due to higher antioxidant enzymatic response and greater rate of photosynthesis in the former.