Aluminium resistance of Norway spruce: Root exudation versus immobilisation in roots

Abstract

Coniferous trees like Norway spruce are widespread on acid soils and tolerate higher Al concentrations than most crop species. The aim of the present work was to understand more completely the relative importance, that exudation of complexing organic and inorganic substances on the one hand, and Al accumulation in roots on the other, play in conferring resistance to Al of Norway spruce. Young plants and seedlings supplied with different levels of Al were grown in hydroculture, and in perlite as a solid substrate. At the end of the growth periods, the nutrient media were analysed for the occurrence of organic substances and phosphorus. Roots in addition to these determinations were also analysed for accumulation and compartmentation of Al. The results suggest that the constitutive exudation of roots of complexing compounds (oxalate, phenolic substances, phosphate) contributes in part to the detoxification of Al in Norway spruce. However, binding of Al in the apoplast, involving complexes with phenolic metabolites, seems to be of greater importance.