Spatiotemporal colonization of Scots pine roots by introduced and indigenous ectomycorrhizal fungi in forest humus and nursery Sphagnum peat microcosms

Mycorrhizal and non-mycorrhizal Scots pine (Pinus sylvestris L.) seedling combinations were grown in two-dimensional Perspex® microcosms containing forest humus or nursery Sphagnum peat, without additional fertilization. Spatial and temporal patterns of mycorrhizal fungal colonization of roots were assessed over a 3-month period, through visual morphotyping and polymerase chain reaction assisted rDNA fingerprinting of developed mycorrhizas. Six distinct morphotypes of mycorrhiza developed on non-mycorrhizal seedlings grown in forest humus. Three of the morphotypes (white1-, black-, and brown-type) were, respectively, associated with the fungi Suillus bovinus (L. ex Fr.) O. Kuntze, Cenococcum geophilum Fr., and Thelephora terrestris Ehrh.:Fr. (= Tomentella radiosa (P. Karst.) Rick). A fourth pinktype morphotype displayed features indicating root colonization by Tomentellopsis submollis (Svrcek) Hjortstam, but this could not be confirmed because of a lack of source restriction fragment length polymorphism (RFLP) data. Brown-type mycorrhiza were the first to appear after seedling transplantation and black-type mycorrhizas showed local and dispersed root colonization dynamics. Mycorrhiza development in the unfertilized nursery peat substrate was restricted to a single unidentifiable brown-type morphotype, which appeared after 44 days. Rapid colonization of adjacent nonmycorrhizal seedlings by Tomentellopsis submollis, but not S. bovinus, was detected following the introduction of preinoculated seedlings into the humus or peat microcosms. The biomass of seedlings grown in nursery peat, regardless of mycorrhizal status, was significantly lower than that of mycorrhizal seedlings grown in humus. These findings support and extend previous bait seedling studies, as they provide a primary in situ characterization of distinct root colonization strategies of mycorrhizal species in forest humus and nursery peat.