Greenhouse climate shapes nitrate levels, nutritional quality, and shelf life in leafy vegetables: species-specific responses

This review synthesizes current knowledge on how greenhouse environmental conditions shape nitrate accumulation, nutritional quality, and shelf-life performance in lettuce, spinach, and rocket. Preharvest climate drivers interactively regulate nitrate reduction, pigment and phenolic biosynthesis, tissue structural integrity, and the physiological mechanisms determining postharvest longevity. These environmental effects influence postharvest performance by regulating carbohydrate reserves, antioxidant capacity, membrane stability, and calcium-mediated tissue integrity, which collectively determine the ability of harvested leaves to maintain metabolic homeostasis during storage. Light intensity and temperature exert the strongest influence, regulating carbon assimilation, nitrate reductase activity, and metabolic homeostasis. Adequate, well-distributed irradiance at moderate temperatures enhances chlorophyll, carotenoids, vitamin C, and phenolics while lowering nitrate levels. In contrast, low light or excessive heat suppress nitrate reduction, dilute pigments and antioxidants, and accelerate senescence. Relative air humidity (RH, via vapor pressure deficit), irrigation regime, and nutrient balance also affect quality by modulating water relations, calcium transport, and leaf structural integrity. Mild irrigation deficit and balanced nitrogen–potassium–calcium supply promote firmer tissues, reduced nitrate accumulation, and slower yellowing, whereas overirrigation or excessive nitrogen produces succulent leaves with limited storability. CO 2 enrichment, diffuse-light films, and targeted mineral or biostimulant inputs can refine nutritional outcomes, although their effects are context-dependent and secondary to light and temperature. Species-specific sensitivities further guide climate optimization. Lettuce is particularly sensitive to low light and high RH, spinach is vulnerable to temperature-driven pigment loss, and rocket depends heavily on light quality and nitrogen balance to maintain antioxidant capacity and limit nitrate accumulation. Overall, harmonizing multiple environmental variables, rather than maximizing individual factors, offers the most effective pathway to achieving low nitrate levels, high nutritional density, and extended shelf life in greenhouse-grown leafy vegetables.