Solution pH modifies the response of Norway spruce seedlings to aluminium

Norway spruce (Picea abies) was exposed to nutrient solutions containing a range of aluminium (Al) concentrations at several pH levels (3.2, 4 and 5). Root growth was reduced by 100 µM and 400 µM Al at pH 4 and 5, but at pH 3.2 only by 400 µM Al. The Al content of the roots increased with increasing pH. The Al content of the roots was higher at the root tips than at the older root parts at all pH values. Using X-ray microanalysis it could be shown that higher levels of Al at increased pH were mainly due to increased Al contents in root cortex cell walls. In seedlings, mycorrhizal with Pisolithus tinctorius or Lactarius rufus, the Al concentration of cortex cell walls was higher when nitrate (NO₃) rather than ammonium (NH₄) was the nitrogen (N) source.