Interactions between nitrogen fertilization and ozone in watermelon cultivar Reina de Corazones in open-top chambers. Effects on chlorophyll a fluorescence, lipid peroxidation, and yield

Watermelon (Citrillus lanatus) plants were grown for two consecutive years in open-top chambers with three different ozone concentrations (O₃-free air, O₃ ambient, and air with additional O₃; CFA, NFA, and NFA+O₃) and three nitrogen fertilizer concentrations 0, 14.0, and 29.6 g N per pot; N0, N1, and N2). There was an interaction between ozone and N fertilizer for the major parameters studied. O₃ and N2 treatments led to a significant decrease in maximum efficiency of photosystem 2 (PS2) photochemistry (F_v/F_m), and induced a significant decrease in the actual quantum yield of PS2 (Φ_PS2), due mainly to the increased closure of PS2 reaction centres (q_P) and to an increase in the non-photochemical quenching (NPQ). On the other hand, these plants exhibited an increased susceptibility to photoinhibition, which could be associated with an increased fraction of reduced Q_A. An increase in lipid peroxidation indicated that damage was occurring at the membrane levels. High N concentration enhanced the detrimental effects of ozone on the fluorescence parameter induction and lipid peroxidation. All these negative alterations led to a decreased yield.