Vitality and bark beetle resistance of fertilized Norway spruce

Abstract

The effects of different so-called vitality fertilizers on the resistance of Norway spruce against back beetles and their associated pathogenic fungi were studied in field experiments. Stem diameter growth, phloem phenolic concentration, resin flow, and reaction to inoculation with Ceratocystic polonica were measured on the trees. The fertilization treatments increased stem diameter growth, but did not affect resin flow, phloem phenolic concentration, or the lesion length caused by the blue-stain fungus. Thus, contrary to expectations based on current theories, we could demonstrate no functional relationship between growth and defence. However, the number of resin canals correlated positively 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 unaffected by fertilization. Thus, although it does not seem possible to markedly increase either the constitutive or the inducible resistance level of Norway spruce through fertilization, vitality fertilization did not reduce the defences in our study and we hypothesize that it can be used without endangering resistance.