Below-ground ectomycorrhizal community structure in two Picea abies forests in southern Sweden

Ectomycorrhizal community structure is likely to be influenced by factors such as anthropogenic stress, site history and degree of isolation. Information about the mycorrhizal community at the level of individual mycorrhizal roots is needed, since these are the organs for nutrient exchange. To identify mycorrhizal species we used morphotyping based on colour and external anatomy of the mycorrhizal roots. The morphotypes were further divided using restriction fragment length polymorphism (RFLP) analysis of the internal transcribed spacer (ITS) region of the ribosomal DNA extracted and amplified from the mycobionts colonizing single mycorrhizal roots. The communities studied were in two similar 60-year-old Picea abies (L.) Karst. forests located in southern Sweden approximately 50 km apart at sites with different N deposition. The level of mycorrhizal colonization was almost 100% at both sites, but the total number of mycorrhizas was 30-42% higher at the northern site. Six morphotypes were distinguished at the northern site with the lower N deposition (Vedby), and four at the southern site (Skrylle). Some morphotypes consisted of several ITS types and identical ITS types were also found in roots assigned to different morphotypes. The RFLP data revealed a total of 16 ITS types. Eleven of these were identified at least to genus by comparison with local or regional reference material. Five ectomycorrhizal taxa, Cenococcum geophilum, Thelephora terrestris, Tylospora fibrillosa, Tylopilus fellelus and Ve-95-3 were common to the two sites but the total number of taxa recorded at Vedby was twice as high as at Skrylle. Possible reasons for the differences between sites are discussed.