Dual function of plasma-activated water in lettuce: growth promoter and nitrogen source under nitrogen-sufficient/-deprived conditions

Cold atmospheric plasma produces reactive oxygen and nitrogen species (RONS) that dissolve in water to form plasma-activated water (PAW). This study investigated the dual function of PAW as a growth-promoting treatment and supplementary nitrogen source for hydroponically cultivated lettuce (Lactuca sativa L. cv. Matilda). Plants were grown in nitrogen-sufficient or nitrogen-deprived half-strength Hoagland solution and subjected to PAW seed priming, cultivation in PAW-activated nutrient solution, or a combination of both treatments. Under nitrogen-sufficient conditions, PAW seed priming increased lettuce fresh weight by up to 40%, chlorophyll content by 25%, and sensory attributes such as freshness and juiciness. Under nitrogen-deprived conditions, PAW partially compensated for nitrogen deficiency, enhanced plant growth and photosynthetic pigment accumulation, increased quercetin content, and stimulated antioxidant enzymes, particularly ascorbate peroxidase and guaiacol peroxidase. Principal component analysis identified nitrogen availability as the main factor determining metabolic and antioxidant profiles, while PAW modulated redox homeostasis in a tissue-dependent manner. These findings demonstrate that PAW-derived reactive species support plant growth through both redox signaling and nitrogen supplementation. PAW therefore represents a promising sustainable approach for improving crop performance, nutritional quality, and stress resilience while reducing conventional fertilizer inputs.