Abstract
Application of a mycosociological method (adaptation of the Lange method) in Central Amazonia produced the following results: In the white-sand podzol campinarana type of forests the dominant trees are obligatorily ectotrophically mycorrhizal; litter is accumulated as raw humus as a consequence of ectotroph dominance; fewer leaf inhabiting litter fungi occur in the dry as well as the wet seasons than are counted in the latosol terra-firme rain forest, and the fungi of that category are most strongly represented ("F-dominance") by other species here than in the terra-firme stands tested. The ectomycorrhizal trees and fungi are enumerated. On the other hand, in the terra-firme forest, ectotrophically mycorrhizal fungi did not occur in the test plots. The trees are almost all non-ectomycorrhizal in primary terra-firme forest; here, litter does not appreciably accumulate as a deep raw humus layer because the considerably higher number of leaf inhabiting litter fungi (ratios of 4:1 to 4.2:1 in favor cf terra-firme) and greater diversification (a larger number of species) is potentially capable of reducing more than the yearly leaf-fall. In this study, a group of fungi was mainly considered which is not represented in laboratory litter decomposition experiments. However, a comparison with unpublished and published data shows that our results satisfactorily match the experimental and phyto-sociological data obtained both with other classes of microorganisms and with observations in other regions. The quantity of litter decomposing fungi in the foliicolous group depends mainly on the amount of precipitation during the last few days before counting. This does not hold for all lignicolous fungi. The reasons for this as well as the mechanisms by which the ectomycorrhizas may reduce litter decomposition rates and influence the nutrient cycling patterns are discussed. The most important genera of Basidiomycetes involved in litter decomposition in the Lower Rio Negro forest associations are enumerated. Possible economic significance of introducing ectotrophs in the terra-firme forest is indicated.