Metabolome reveals high nitrogen supply decreases the antioxidant capacity of blue honeysuckle (Lonicera caerulea L.) by regulating flavonoids.

The objectives of this research were to analyze the effects of varying nitrogen application rates on fruit quality and antioxidant properties of blue honeysuckle through widely targeted metabolomics analysis. High nitrogen application resulted in a reduction in fruit size and soluble solid content, along with significant decreases in the levels of total anthocyanins, phenolic compounds, flavonoids, and antioxidant indices. Under low nitrogen, key flavonoids in fruit namely Kaempferol-7-O-glucoside, Morin 3-alpha-L-lyxopyranoside, and Quercetin-3-O-xyloside (Reynoutrin) showed the high peak areas, with SOD, POD, and CAT activities at 1742.19, 45,525.65, and 1065.13 U/g, but decreased under high nitrogen. The molecular docking analysis revealed affinity values of -5.39, -2.72, -4.37, -3.98, -4.04, -4.18, -2.51, -2.31, and - 4.08 kcal/mol for SOD, POD, and CAT. These three flavonoids play a crucial role in the antioxidant defense system by targeting different enzymes, and their reduced concentrations under high nitrogen conditions may impair the fruit's antioxidant capacity.