DOES NITROGEN-FERTILIZATION HAVE AN IMPACT ON THE TRADE-OFF BETWEEN WILLOW GROWTH AND DEFENSIVE SECONDARY METABOLISM

The effect of nitrogen fertilization on the phytomass production, shoo t length and leaf secondary phenolics in nine Salix myrsinifolia clone s was investigated. Cuttings taken from 1-year-old and 2-year-old shoo t parts of field cultivated clones were grown at three concentrations of nitrogen (7, 150 and 300 ppm) in a greenhouse for one growing seaso n. The willow clones differed significantly in phytomass yield and sec ondary phenolics content. Nitrogen fertilization affected significantl y the growth and secondary metabolism of willow clones. In most clones , the addition of nitrogen from a sub-optimum concentration (7 ppm) to an optimum concentration (150 ppm) appeared to reduce the amounts of salicortin, chlorogenic acid and unknown salicylate and increased shoo t phytomass, but a supra-optimum nitrogen concentration (300 ppm) resu lted in highly variable growth and secondary phenolic responses. A sig nificantly negative correlation between leaf phytomass and amount of t otal phenolics at sub-optimum and optimum N-treatments indicates trade -off between growth and secondary metabolism in willow clones at these treatments. However, the leaf phytomass:total amount of phenolics rat io varied significantly among clones, and in all clones it was not sig nificantly lower at sub-optimum N-treatment than at optimum N-treatmen t.