Effects of vitality fertilization on the resin flow and vigour of Scots pine in Finland

Abstract

The vitality and defence of Scots pine were measured in order to study how different fertilizer combinations affect these traits, and to determine whether an increase in growth leads to reduced defence as predicted by the theories based on the assumption of the existence of a trade-off between growth and carbon-based defence compounds. Stem diameter growth and vigour index were measured as indicators of vitality and stem resin flow and the concentration of phloem phenolics were used as indicators of defence level. Fertilizer treatments containing nitrogen had a growth-promoting effect and the vigour index was higher in the nitrogen-fertilized treatments than in the control and non-nitrogenous fertilizer treatments. Four of the ten experimental sites were situated along a heavy metal pollution gradient at 0.5, 2.5, 4 and 8 km distance from the emission source. The vigour index in the severely polluted site closest to the emission source was considerably lower than that in the other three sites along the gradient, but even there nitrogen gave a clear growth response. In spite of the large within- and between-tree variation in resin flow, the average resin exudation differed little between the experimental sites. In most sites the resin flow was highest in the control treatment. A weak negative correlation was found between resin flow and vigour index. In the pollution gradient the mean resin flow was lowest at the most polluted site and increased along the gradient up to 4 km from the emission source. The phenolic concentration of the phloem was not affected by fertilization in any of the experiments apart from the severely polluted one. Indications of a weak negative linear correlation between vigour index and phloem phenolics were found. There was no significant correlation between the phenolic concentration and the amount of resin flow in any of the different sites. Except for the liming treatment in the polluted experiments, we did not detect any response to non-nitrogenous fertilizer treatments.