Anthocyanin-rich extract from grape pomace enhances the quality and yield of hydroponic lettuce by modulating carbon-nitrogen metabolism.

Anthocyanins are regarded as natural biostimulants with significant potential in agricultural production. We investigated the effects of an anthocyanin-rich extract from grape pomace (ACNs) on the yield and quality of hydroponic lettuce. The most balanced improvements in growth and quality were achieved with 2 g L-1 ACNs. ACNs significantly increased shoot biomass, elevated the levels of total phenolics, flavonoids, anthocyanins, and antioxidant activity, while concurrently reducing nitrate accumulation. These changes were accompanied by upregulated enzyme activities and transcript levels in phenolic biosynthesis and nitrogen assimilation pathways, together with enhanced photosynthetic performance. Metabolomic analysis further revealed that ACNs modulated carbon and nitrogen metabolism, promoting a shift in metabolic profiles toward the accumulation of health-promoting phenolic compounds. Therefore, grape pomace-derived anthocyanins can serve as an effective elicitor to improve both the yield and nutritional quality of lettuce, offering a promising strategy for the valorization of winery byproducts into functional vegetables.