Resistance of fertilized Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.)

The ability to react to wounding with resin flow and rapid synthesis of defence chemicals is an important means of resistance in conifers. Strong resin flow and rapid accumulation of phenolics and stilbenes in the phloem around a wounded site can prevent the invasion of bark beetles and associated fungi. As growth is considered the primary sink for assimilates, a relationship, even a trade-off is expected to exist between growth and defense. We have tested how fertilization can affect resin flow and phloem phenolics in Norway spruce, Picea abies, and Scots pine, Pinus sylvestris, in Norway spruce, nitrogen fertilization increased the stem diameter growth and the vigour index, but did not affect resin flow, phloem phenolic concentrations or the lesion length caused by C. polonica. However, in Scots pine, with low vigour index resin flow was either weak or strong, whereas trees with high vigour index were never associated with high resin or phenolic content. The observation that high vigour and strong defense never occurred together is in agreement with the growth-differentiation balance hypothesis.