Species diversity and distribution of biomass above and below ground among ectomycorrhizal fungi in an old-growth Norway spruce forest in south Sweden

Abstract

The structure of an ectomycorrhizal community was assessed on a 100-m² plot in a 100-year-old, oligotrophic Norway spruce, Picea abies (L.) Karst., forest in southern Sweden. During the 6-year study (1986–1992) sporocarps were identified and their biomass determined. Late in the fall of 1993, we identified mycorrhizas and estimated their abundance. Forty-eight epigeous, ectomycorrhizal taxa were identified based on the examination of sporocarps. Hygrophorus olivaceoalbus (Fr.:Fr.) Fr. and six species of Cortinarius, i.e., C. acutus (Pers.:Fr.) Fr., C. brunneus (Pers.:Fr.) Fr., C. evernius (Fr.:Fr.) Fr., C. obtusus (Fr.) Fr., C. paleaceus Fr., and C. strobilaceus Moser, were found every year. For the period as a whole, they accounted for 32% of the annual sporocarp biomass. Twenty-one species were observed during 1 year only. Cenococcum geophilum Fr. and Piloderma croceum Erikss. & Hjortst. accounted for 18 and 19%, respectively, of the mycorrhizal abundance of the mycorrhizal root tips examined. Using polymerase chain reaction (PCR) based molecular methods, we were able to distinguish 25 taxa forming mycorrhiza from soil cores covering a total of 22.5 cm² of the forest floor. Twelve of these taxa were identified using a sporocarp or mycelial culture based reference data base containing 25 of the sporocarp-producing species. These 12 species accounted for an average of 74% of the sporocarp biomass. In contrast, their share of the estimated mycorrhizal abundance and biomass was about 30%. At least half of the abundance of the belowground ectomycorrhizal community was accounted for by species that did not produce conspicuous epigeous sporocarps. Ascomycetes accounted for about 20% of the mycorrhizal abundance. Calculations showed that on a per hectare basis there was 8.8 kg of fungal biomass in the form of sporocarps (average annual cumulative production), an estimated 250–400 kg as mycorrhiza (standing crop) and 440 kg in the form of sclerotia of Cenococcum geophilum (standing crop). Key words: ectomycorrhizal community structure, ITS–RFLP, Picea abies.