Nitrogen-induced changes in phenolics of Vaccinium myrtillus--implications for interaction with a parasitic fungus

The effects of nitrogen (N) fertilization on the phenolic status of Vaccinium myrtillus leaves were studied to assess whether N amendment affects the potentially defensive phenolic metabolites in a way that could have consequences for the interaction with a parasitic fungus (Valdensia heterodoxa). Healthy (symptomless) and V. heterodoxa-infected leaves were collected from plants grown in the understorey of a boreal coniferous forest, where they received no additional N or either a moderate or a high dose of N fertilizer. Leaf samples were taken during a single growth season and analyzed for individual phenolics using HPLC. The effect of a moderate N dose on the concentration and content of phenolics was in most cases nonsignificant. In contrast, the high N dose resulted in pronounced effects. In healthy leaves, N fertilization reduced concentration of three of five individual phenolics. Moreover, fertilization with high dose of N accompanied by infection by V. heterodoxa often increased the concentration and content of phenolics as compared to unfertilized plants. Addition of N had no significant effect on the growth of the analyzed V. myrtillus leaves, and the N-induced variation in phenolic levels seemed to be due to changed rate of their production. The concentration and content of phenolic metabolites in healthy leaves collected from unfertilized plots fluctuated compound-specifically during the growth season, and the phenolic responses to N and infection showed temporal and compound-specific variations.