Nitrogen allocation and trade-off among growth and defense strategies of ornamental herbaceous plants exposed to increasing ozone concentrations

Nitrogen (N) allocation and trade-offs across primary and secondary metabolic pathways help to evaluate plant adaptive capacity to harsh environmental conditions. Tropospheric ozone (O 3 ) is a major concern for ecosystem health, particularly in highly polluted cities like those of China. Here, Salvia splendens , Zinnia elegans and Helianthus annuus plants were exposed to ambient air (AA), moderate (AA+40 ppb, AA+40) and elevated (AA+80 ppb, AA+80) O 3 concentrations to explore interspecific differences in N allocation and O 3 -response strategies. Photosynthetic rate (A) of S. splendens increased at 15 and 32 days from the beginning of the exposure (FBE; +24 % on average) under AA+ 40, whereas decreased in Z. elegans under both AA+ 40 and AA+ 80 (-24 %, on average, at 15 days FBE), and in H. annuus under AA+ 80 (-18 % at 32 days FBE). AA+ 80 reduced N based on leaf area (N area ) in all the three species. In addition, in S. splendens , AA+ 40 promoted N allocation to photosynthesis (N photo ; +10 % at 32 days FBE) and decreased the N allocation to cell wall (N CW , -24 % throughout the entire exposure period), whereas in Z. elegans N photo was decreased at 15 and 48 days FBE (-38 %, on average) and no change was reported in N CW . Differently, both N photo and N CW decreased under AA+ 80 in all the three species. AA+40 maintained or improved the biomass production of S. splendens and Z. elegans , whereas H. annuus growth was inhibited. Overall, S. splendens and Z. elegans better adapted to AA+ 40 compared to H. annuus , which was attributed to increased contributions of N photo and N to chemical defense, highlighting species-specific strategies in adapting to O 3 -stress conditions. • Nitrogen (N) allocation/trade-off affects plant adaptation to ozone (O 3 ) pollution. • Ornamental salvia, zinnia and sunflower show species-specific adaptation to O 3 . • Salvia is more tolerant to O 3 in terms of photosynthetic and growth responses. • N allocation to photosynthesis plays a crucial role in salvia’s tolerance to O 3 . • Salvia is a good candidate for urban green spaces in O 3 -polluted areas.