Rare earth elements in shungite-bearing soils: content, distribution and specific mycorrhiza formation

The paper presents the results of the study of the content and distribution of rare earth elements (REE) in the soils formed over shungite rocks in Zaonezhye (Russia, Karelia). The mean gross content of REE in the soils confined to undeveloped shungite outcrops (Podsosonye, Lebeshchina, Karnavolok) remote from the sources of man-made burden is 57 mg/kg. This is lower than the REE content in the soils of Maksovo and Zazhogino quarries that is 78 mg/kg. REE concentrations in shungite soils are below the average bulk earth values. A topological similarity was found in the patterns of REE distribution in shungite rocks and the soils, which manifested itself in the predominance of light over heavy REE (∑LREE / ∑HREE = 5 - 7) and in the presence of a negative Eu anomaly. A slight REE accumulation in the soil was observed (soil enrichment factor), its rate depending on the organic matter content and acidity of the soils. Specific mycorrhiza formation patterns were identified in spruce growing on the soils above the shungite rocks. The thickness and share of a mycelial sheath in the ectomycorrhizal tip of spruce growing in soils above shungite rocks were greater than those of the spruce ectomycorrhizae from the conditionally reference site. There the density of spruce ectomycorrhizae is twice as high as that in the spruce growing on shungite-bearing soils. It was stated that there were correlations between the REE content in soil and the values of ectomycorrhizal parameters. For ectomycorrhizae of the spruce trees growing on the soils above the non-developed shungite rock outcrops positive correlations were detected between REE content and the values of the fungal mycorrhiza component. As for the ectomycorrhizal parameters of the spruce trees growing in the immediate vicinity of the active shungite quarry negative correlations between the soil REE content and the ectomycorrhiza plant component were noted.