VITALITY AND BARK BEETLE RESISTANCE OF FERTILIZED NORWAY SPRUCE

The effects of different so-called vitality fertilizers on the resista nce of Norway spruce against bark beetles and their associated pathoge nic fungi were studied in field experiments. Stem diameter growth, phl oem phenolic concentration, resin flow, and reaction to inoculation wi th Ceratocystis polonica were measured on the trees. The fertilization treatments increased stem diameter growth, but did not affect resin f low, phloem phenolic concentration, or the lesion length caused by the blue-stain fungus. Thus, contrary to expectations based on current th eories, we could demonstrate no functional relationship between growth and defence. However, the number of resin canals correlated positivel y with tree vigour, and there were indications of a potential increase in this constitutive defence feature after fertilization. Resin flow increased two-fold in the trees wounded 1 year earlier, indicating an induced component in resin production. This induced mechanism was unaf fected by fertilization. Thus, although it does not seem possible to m arkedly increase either the constitutive or the inducible resistance l evel of Norway spruce through fertilization, vitality fertilization di d not reduce the defences in our study and we hypothesize that it can be used without endangering resistance.