Patterns of arbuscular- and ecto-mycorrhizal colonization of Eucalyptus dunnii in southern Brazil.
After planting Eucalyptus dunnii, virtually free of mycorrhizal colonization, at six sites in Santa Catarina and Paraná states, S. Brazil, three distinctive patterns of root colonization by arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi were discerned during the ensuing 13 months. The soils of the 5 sites which had had previous tree crops were Oxisols, with organic matter of 4.2 to 6.5%, pH 3.8 to 4.0, and extractable phosphorus (P) of 2.6 to 3.8 p.p.m.; the sixth, agricultural site, had an Inceptisol with 2.7% organic matter, pH5.4 and extractable P 11.0 p.p.m. Three patterns of mycorrhization occurred, which appeared to be very strongly related to previous cropping: (1) pattern A was on the agricultural site, preceded by the AM-forming soya bean [Glycine max] - the relatively large incidence of AM 5 months after planting progressively decreased while that of ECM increased; (2) pattern B followed the AM/ECM-forming Eucalyptus viminalis - the incidence of AM remained minimal while that of ECM relatively rapidly reached a high plateau; and (3) pattern C followed the ECM-forming Pinus taeda - both AM and ECM progressively increased but were never abundant. Although the results do not fully explain the three patterns of colonization, it is suggested that the inoculum potential and the specificity of fungi-host relations are implicated.