On the northern California coast, mixed conifer forests occur on younger, relatively fertile terraces, whereas mesic and hydric pygmy forests occur on older, infertile, poorly drained terraces. We characterized mycorrhizal associations, ectomycorrhizal morphotypes, and colonization levels for nine plant species from three plant communities (mixed conifer, mesic pygmy, and hydric pygmy). Pinus contorta ssp. bolanderi (Parl.) Critchf. and Pinus muricata D. Don were ectomycorrhizal; all ericaceous plants formed ericoid mycorrhizas except Arctostaphylos nummularia A. Gray, which formed only arbutoid mycorrhizas. Arbuscular mycorrhizas were not observed, even on Cupressus goveniana ssp. pigmaea (Lemmon) J. Bartel. Ectomycorrhizal colonization was significantly lower in pygmy forests, while ericoid mycorrhizal colonization was significantly higher, as compared with the mixed conifer forest. Ectomycorrhizal and ericoid mycorrhizal colonization was greater on hummocks than in swales at hydric pygmy sites. Thirteen distinct ectomycorrhizal and arbutoid mycorrhizal morphotypes were observed: eight only on Pinus spp. and two only on A. nummularia. Two morphotypes were found only in mixed conifer, and eight were found only in pygmy communities. Distribution of morphotypes may reveal habitat and (or) host adaptation by ectomycorrhizal fungi.Key words: ectomycorrhizal morphotypes, ericoid mycorrhizas, pygmy forest, Ericaceae, mycorrhizal colonization, low-fertility soils.
Exclusion of grass roots from soil organic layers by Calluna: the role of ericoid mycorrhizas
