Distribution of lead in mycorrhizal and non‐mycorrhizal Norway spruce seedlings

Abstract

Non‐mycorrhizal spruce seedlings(Picea abies Karst.) and spruce seedlings colonized with Lactarius rufus (Scop.) Fr. or two strains of Paxillits involutus (Batsch) Fr. were grown in an axenic silica sand culture system with frequently renewed nutrient solution. After successful mycorrhizal colonization, the seedlings were exposed to 1 μM PbCI2 for 19 weeks. The degree of infection in all of the mycorrhizal treatments approached 100% during the experiment and was not affected by exposure to Pb. However, the number of root tips per root dry weight and the shoot: root ratio, both in the non‐mycorrhizal and the mycorrhizal seedlings, had decreased after the 19 week treatment with PbCl2 Using X‐ray microanalysis, the distribution and concentration of Pb in the tissues of mycorrhizal and non‐mycorrhizal root tips were compared. In the mycorrhizae of seedlings exposed to Pb no significant accumulation of Pb in the hyphal mantle or in fungal cell walls of the Hartig net were detected. Lead accumulated primarily in the cortex cell walls both of non‐mycorrhizal and mycorrhizal root tips. No significant difference of Pb concentrations in root cortex cell walls of non‐mycorrhizal and mycorrhizal seedlings was found; except for seedlings colonized with Paxillus involutus strain 537. However, at the endodermis no effect of mycorrhizal fungal colonization on the Pb tissue concentration was detected. The presence of the fungal sheath did not prevent Pb from reaching the root cortex. The endodermis acted as a barrier to Pb radial transport in both mycorrhizal and non‐mycorrhizal seedling roots.