RESOURCE PARTITIONING TO GROWTH, STORAGE AND DEFENSE IN NITROGEN-FERTILIZED SCOTS PINE AND SUSCEPTIBILITY OF THE SEEDLINGS TO THE TARNISHEDPLANT BUG LYGUS-RUGULIPENNIS

We tested how variable nitrogen availability affects the above- and be low-ground growth of first-year Scots pine (Pinus sylvestris L.) seedl ings and carbon allocation to defensive allelochemicals and storage. C oncentrations of free amino acids were considered as indicators of nut ritive quality. Suitability of seedlings for polyphagous Lygus rugulip ennis Popp. (Heteroptera: Miridae) was tested with oviposition prefere nce and nymphal growth experiments. At the end of the growing season, needle length increased while root biomass decreased with elevated N f ertilization, but shoot length was not affected. Concentration of star ch in needles and roots, representing carbon storage, was not signific antly affected by N fertilization, although there was a decrease in th e starch concentration of needles when nitrogen input increased. Nitro gen fertilization significantly increased the pool of total and noness ential amino acids in the shoots. Arginine, proline and glutamine were the individual amino acids most affected by elevated N. Of the carbon -based defence compounds, total resin acid concentrations in shoots we re significantly reduced with elevated nitrogen in 9-wk-old seedlings. Palustric acid and neoabietic acid were the most affected individual resin acids, whereas foliar monoterpenes were not influenced by N avai lability. Total phenolics in shoot and root showed variable response. The increasing effect of nitrogen on the oviposition rate of Lygus fem ales was almost linear. Mean relative growth rate of the nymphs was si gnificantly affected by the level of N fertilization, but the mortalit y of nymphs was high in all treatments. The results suggest that in ni trogen-rich environments the needle growth of small Scots pine seedlin gs is improved, but their susceptibility to insect attack is increased and they remain less defended as predicted by the carbon/nutrient bal ance hypothesis. Total phenolics and resin acids, representing phenyla lanine and mevalonic acid pathways, respectively, were both reduced by increased nitrogen availability. Together with the simultaneous incre ase of foliar free nitrogen in the form amino acids, the nutritive val ue of seedlings is ameliorated and this might explain susceptibility o f nursery-grown, N fertilized seedlings to polyphagous Lygus bugs.