Abstract
The present study investigates the efficiency of nitrogen (N) amendments in the management of ozone (O(3)) stress in two varieties (Kashi Sheetal and Kashi Harittima) of Indian bean (Dolichos lablab L.). Two O(3) concentrations, ambient (44.9 ppb) and elevated (74.64 ppb) were used, and each O(3) 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 O(3) tolerant, as compared to Kashi Harittima. N amendments were effective in the partial amelioration of O(3) stress, with N2 being the most effective nitrogen dose, at both ambient and elevated O(3) concentrations. Kashi Sheetal has been determined to be O(3) tolerant due to greater endogenous levels of H(2)O(2) accumulation and enzymatic antioxidant contents with O(3) exposure. The O(3)-sensitive variety, Kashi Harittima, responded more positively to N treatments, at both O(3) 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 (O(3) sensitive), as compared to Kashi Sheetal (O(3) tolerant) at both ambient and elevated O(3) concentration, due to higher antioxidant enzymatic response and greater rate of photosynthesis in the former.