The effect of u.v.‐B radiation on u.v.‐absorbing secondary metabolites in birch seedlings grown under simulated forest soil conditions

Abstract

summary Birch ( Betula pendula Roth) seedlings were grown under enhanced u.v.‐B radiation and simulated forest‐soil conditions, after which individual secondary metabolites were determined in the leaves. It was found that not all of the u.v.‐absorbing secondary metabolites of the seedlings responded to supplementary u.v.‐B radiation. Under increased u.v.‐B radiation, significant increases in concentration were observed only for the major flavonoid, quercitrin, the minor fiavonoid, myricetin‐3‐galactoside, and for chlorogenic acid. On the other hand, 3,4′dihydroxypropiophenone‐3‐β‐D‐glucopyranoside decreased under u.v.‐B irradiation. The concentration of phenolic compounds in the leaves changed during the growing season (between two harvests) but this change was not related to u.v.‐B enhancement. A low availability of mineral nutrients did not impair the capacity of the seedlings to accumulate u.v.‐protecting phenolic compounds under increased u.v.‐B radiation. The growth conditions used might have affected the intracellular concentrations of secondary metabolites, and thus furnished the birch seedlings with an increased tolerance of u.v.‐B radiation. These findings point to the significance of certain phenolic components in the protection of deciduous trees against u.v.‐B radiation.