Interaction between high nitrate levels and chloride nutrition: effects on physiological responses and nutritional quality in lettuce baby leaves

Resúmen de la comunicación oral presentada en el XVIII Simposio Hispano-Luso de Nutrición Mineral de las Plantas-NUTRIPLANTA2024 22 a 24 de julioBadajóz (2024)

Traditionally, chloride (Cl¿) has been considered a detrimental element for agriculture when present in high concentrations in the soil, as in saline conditions, because it was commonly believed to negatively interact with the uptake of nitrate (NO3¿) in higher plants. Nitrate is the primary nitrogen (N) source for plants, being an essential element for growth and development and a signaling molecule involved in numerous physiological processes. Since Cl¿ and NO3¿ share transporters in roots, it is thought that high Cl¿ concentrations in the medium can alter NO3¿ uptake, reducing plant yield and affecting growth and development. However, our previous studies have demonstrated that applying Cl¿ at a typical macronutrient levels (1-5 mM) in the nutrient solution improves plant growth and development under optimal NO3¿ nutrition. When accumulated in leaves at macronutrient levels, Cl¿ promotes specifics physiological functions that lead to a higher efficiency in the use of water (WUE) and N (NUE), a better photosynthetic performance and N assimilation and drought resistance (Franco-Navarro et al., 2016, J Exp Bot 67:873; 2019, Plant J 99:815; 2021, J Exp Bot 72:5246; Rosales et al., 2020, Front Plant Sci 11:442; Peinado-Torrubia et al., 2023, Front Plant Sci 13:1058774). In agriculture, the NO3¿ over-fertilization can adversely affect crop yield and generate environmental problems like water pollution, being harmful to people and nature. Besides, high NO3¿ amounts in leaves can also reduce the nutritional quality of leafy vegetables and become a serious risk for human health. With this background, we studied the effect of Cl¿ nutrition, applied at both macronutrient and mild salinity levels, on the shoot growth of young lettuce plants grown under increasing NO3¿ treatments ranging from optimal to toxicity levels (i.e. 5-25 mM NO3¿). Considering the lettuce's capacity for NO3¿ over-accumulation and the significant economic impact due to its consumption as baby leaves, we also focused on how Cl¿ vs. NO3¿ nutrition can improve yield and nutritional quality by altering the accumulation of antioxidant compounds. Furthermore, a series of antioxidant tests have been analyzed in lettuce leaves: DPPH, Reducing Power, and FRAP assays, as well as the amount of total phenols and flavonoids. Additionally, the total amount of Cl¿ and NO3¿, and the malondialdehide (MDA) as an indicator of lipid peroxidation, were analyzed in lettuce leaves under the different Cl¿ /NO3¿ treatments.