Root architecture and root/shoot-ratios of Norway spruce as affected by thinning intensity and soil type in Denmark

Abstract

This paper deals with the structural root systems and the root/shoot-ratios in Norway spruce. 10-16 trees were excavated in each of three thinning plots, replicated on a very fertile clayey and a very poor sandy soil. Root architecture, stem volume and crown fresh weight were assessed. The total number of lateral roots near the stump was independent of site and thinning intensity. The number of “dominant” roots among the total number of roots near the stump also seemed unaffected. It is assumed that these parameters are strongly genetically controlled. The number of roots at 1 meter distance from the stump center was highest on the poor site. As the roots/stem-ratio also showed significant higher values on the poor site, whereas the roots/crown-ratio was unaffected by site, it is concluded that crown and roots are stronger sinks on a poor than on a fertile site. The roots/stem-ratio also increased with increasing thinning intensity on both sites. The results show that the architecture of Norway spruce trees adapts to an environment in a rational way in order to deal with different stresses: Trees respond to an increased wind load with an increased allocation of carbohydrates to the structural roots — enhancing the roots/stem-ratio; and low level water- and nutrient-supply affects increased root branching frequency and root/shoot- ratio.