OCCURRENCE AND INFECTIVITY OF ARBUSCULAR MYCORRHIZAL FUNGI IN SOME NORWEGIAN SOILS INFLUENCED BY HEAVY-METALS AND SOIL PROPERTIES

Mycorrhizae are ubiquitous symbiosis which can mediate uptake of some plant nutrients. In polluted soils they could be of great importance i n heavy metal availability and toxicity to plants. Mycorrhizae have al so been reported to protect plants against toxic metals. We investigat ed the occurrence and infectivity of arbuscular mycorrhizal (AM) spore s as affected by heavy metal levels and other soil properties in Norwe gian soils collected from heavy metal polluted, high natural backgroun d and non-polluted areas. Spore numbers, mycorrhizal infectivity and s pore germination of indigenous mycorrhizal fungi and of a reference st rain (Glomus mosseae) in soils showed lower values in two soils with h igh metal concentrations and in one soil with a low pH. Mycorrhizal in fectivity was negatively correlated with extractable metals. Spore num ber and mycorrhizal infectivity in a soil with naturally high heavy me tal content were not different to in non-polluted soils, and indigenou s AM fungi appeared more tolerant to metals than those in non-polluted soils. Mycorrhizal infectivity, expressed as MSI(50) values, was sign ificantly correlated (r(1) = 0.89, p < 0.05) with the percentage of ge rminating G. mosseae spores in the soils. However, the number of spore s per volume of soil was not significantly correlated with infectivity or spore germination of the reference strain. The spore germination m ethod is discussed as a bioassay of heavy metal toxicity in soil.