The role of boron in below-ground and above-ground growth of Norway spruce (Picea abies) trees and seedlings

Abstract

A short term pot experiment in a growth room and long-term field fertilisation experiments were used to study the effects of boron on the below-ground and above-ground growth of Norway spruce seedlings and trees. In the short term pot experiment, B treatments were applied in the nutrient solution. Three different levels of boron supply were used ranging from deficiency levels up to optimal ones. Furthermore, a drought period of nine days was imposed to one half of the seedlings at the end of the experiment. The results of this experiment clearly showed that low internal boron decreases the number of fine roots and root dry weight in Norway spruce seedlings. The seedlings grown with adequate internal B had more root tips than those receiving the lower B treatments, when needle B concentrations at the lowest B supply were 16–17 mg kg−1, which has earlier been considered as a sufficient B level. Boron had only a slight effect on above-ground growth of the seedlings before the drought treatment. However, the seedlings with low internal B grew significantly less when exposed to drought, which indicates reduced drought resistance in these seedlings. In long term field fertilisation experiments, B fertiliser was applied to experiments at the rate of 1.5kg B ha−1 in June, 1989. Boron increased needle B concentrations even ten years after the fertilisation. Annual volume growth, fine root biomass, fine root length and number of root tips were increased in a fertile site, but the effect was smaller or absent in a less fertile site.