Norway spruce (Picea abies) was exposed to nutrient solutions containi
ng a range of aluminium (Al) concentrations at several pH levels (3.2,
4 and 5). Root growth was reduced by 100 mu M and 400 mu M Al al pH 4
and 5, but at pH 3.2 only by 400 mu M 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 incr
eased pH were mainly due to increased Al contents in root cortex cell
walls. In seedlings, mycorrhizal with Pisolithus tinctorius or Lactari
us rufus, the Al concentration of cortex cell walls was higher when ni
trate (NO3) rather than ammonium (NH4) was the nitrogen (N) source.