A survey of micorrhizal infection in an amazonian rain forest

A survey of mycorrhizal infection and depth of rootlets was carried out on a hectare of primary rain forest in which all individuals over 15 cm in diameter had been identified and labeled. Non-mycorrhizal, lightly infected, moderately infected, and heavily infected species made up 16.7, 23.2, 14.8, and 16.7%, respectively, of the total plot's ecological importance value. Of the plot's total importance value, 59.9% were found to have fine roots in the 0- to 10-cm depth range, 7%. to be in the 10-to 30-cm range, and 7.9% to have roots deeper than 30 cm. A strong association was found between root depth and mycorrhizal condition, with surface roots much more likely to be infected than deep roots. Rootlet depth was shown to be a consistent trait within a species and most often within a genus. The deep-rooted, non-mycorrhizal condition was interpreted as an ecological "strategy" for avoiding competition with more efficient mycorrhizal species.