Metal Toxicity in Mycorrhizal Norway Spruce Seedlings

Abstract

Mycorrhizal and non-mycorrhizal spruce seedlings (Picea abies Karst.) were grown in an axenic quartz sand culture system with frequently renewed nutrient solution. The seedlings were exposed to either 1 μM PbCl2 or 800 μM Al (NO3)3 for 13 to 19 weeks. Using X-ray microanalysis, the distribution and content of Pb and Al in mycorrhizal and non-mycorrhizal root tips have been compared. Independent of mycorrhizal colonization and fungal species the highest contents of Pb and Al were found in the apoplast of the root cortex. Except for seedlings colonized with Paxillus involutes strain 537 and exposed to Pb, no significant difference in Pb or Al contents in cell walls of the root cortex of mycorrhizal and non-mycorrhizal root tips was found. In the mycorrhizal seedlings exposed to Al, contents of Mg in needles and roots were strongly reduced. This reduction was attributed to Al displacing Mg in the root cortex cell walls. The results indicate that the fungal sheath does not prevent Al and Pb from uptake into the root.