Secondary metabolites and nutrient concentrations in silver birch seedlings under five levels of daily UV‐B exposure and two relative nutrient addition rates

Summary Changes in secondary metabolites in silver birch ( Betula pendula ) seedlings are presented in response to ultraviolet‐B radiation (UV‐B) and nutrient addition. Concentrations of individual secondary metabolites and nutrients were measured in leaves of greenhouse‐grown silver birch seedlings exposed to five time‐integrated irradiances of biologically effective UV‐B (I BE UV‐B ) and fertilized with two relative nutrient addition rates. Several phenolics were not only induced by UV‐B, but their concentration was dependent on UV‐B daily time‐integrated irradiance. Relative nutrient addition rate also affected the concentration of phenolics but had little effect on the UV‐B daily time‐integrated irradiance‐responses. The mineral nutrient concentration of leaves was affected by nutrient addition but not by increasing I BE UV‐B . Possible threshold‐exposures for the accumulation of secondary metabolites or nutrients were not detected. UV‐B and relative nutrient addition rate have mainly an additive (rather than synergistic) effect in silver birch, and leaves respond to increasing UV‐B by synthesizing metabolites (e.g. flavonols), which are important UV‐B filters. This study reports the first UV‐B‐exposure‐response curves for individual secondary metabolites and nutrients in leaves of a woody tree species.