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The species composition, succession and biomass production of ectomycorrhizal (ECM) sporocarps were studied during early primary succession on Mount Fuji, Japan, with special reference to developmental stages and the growth of associated hosts.

Weekly sporocarp surveys were conducted over 2 yr on a volcanic desert, where the total vegetation coverage was about 5%. We also quantified the growth of associated hosts in terms of size, photosynthesis, and leaf N and P concentration.

A total of 11 450 sporocarps of 23 species were recorded. They were associated almost exclusively with an alpine dwarf willow, Salix reinii . Two Laccaria and one Inocybe species were the first colonizers; subsequent fungal species were added as the host grew. There was no evidence of any fungus disappearing and being replaced in the sere of ECM fungal succession.

The biomass production of ECM sporocarps was exceptionally large, in general, and amounted to 19% of leaf biomass in the most productive associations. Annual ECM sporocarp production in individual ECM associations was strongly correlated with the growth of the associated host, especially with the photosynthetic rate, which appeared to be determined by leaf N and P concentration.