The effect of aluminium on uptake and distribution of magnesium and calcium in roots of mycorrhizal Norway spruce seedlings

Abstract

Spruce seedlings (Picea abies (L.) Karst.) colonized with Lactarius rufus (Scop.) Fr. or Lactarius theiogalus Fr. were grown in an axenic silica sand culture system with frequently renewed nutrient solution. After successful mycorrhizal colonization the seedlings were exposed to 800 μM Al(NO3)3 (pH 3.9) for 13 or 17 weeks. Concentrations of Al, Mg, and Ca in the tissues of the mycorrhizal root tips were determined by X‐ray microanalysis. After 13 or 17 weeks of exposure to Al, high Al concentrations were found in cell walls of all mycorrhizal tissues except the stele tissues. Compared to the controls Mg levels in most of the mycorrhizal structures were reduced by Al treatment. Calcium levels in cortex cell walls of root tips colonized with L. rufus were reduced by exposure to Al. However, in cell walls of the stele Ca levels were significantly increased. No differences in Al or Mg levels were detected in structures of mycorrhizal and non‐mycorrhizal root tips from the same individual seedlings. These results suggest that (1) the endodermis is the primary barrier to radial Al transport and (2) the presence of a hyphal sheath did not prevent Al from reaching the root cortex and from displacing Mg and Ca.