A survey of micorrhizal infection in an amazonian rain forest

T V.St John

doi:10.1590/1809-43921980103527

Abstract

Abstract 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.

Highlights

In spite of the known importance of mycorrhizal fungi in mineral nutrition of plants (Gerdemann, 1975; Bowen. 1973) and much speculation about the importance of these fungi in t ropical ecosystems (Mc l ean, 1919; Richards, 1953, Went & Stark, 1968), such basic ecological data as distribution and abundance of infection in tropical forests remain scarce
An index of importance value was calculated for each species as a means of identifying dominant or ecologically significant species in the forest
Since only one quadrat was used and ali species occurred on it, the frequency values are ali equal and this measure contributes nothing to the importance value index

Summary

INTRODUCTION

In spite of the known importance of mycorrhizal fungi in mineral nutrition of plants (Gerdemann, 1975; Bowen. 1973) and much speculation about the importance of these fungi in t ropical ecosystems (Mc l ean, 1919; Richards, 1953, Went & Stark, 1968), such basic ecological data as distribution and abundance of infection in tropical forests remain scarce. 1973) and much speculation about the importance of these fungi in t ropical ecosystems (Mc l ean, 1919; Richards, 1953, Went & Stark, 1968), such basic ecological data as distribution and abundance of infection in tropical forests remain scarce. A study of an area of primary tropical ri:li n forest in which ali individuais had beP.n identified and labeled (Prance et a/., 1976) offered an cpportunity to obtain such data in some detail. An index of importance value was calculated for each species as a means of identifying dominant or ecologically significant species in the forest. Species with high importance value were given prionty in sampling. The depth at which each root sample was recovered was recorded

METHODS AND MATERIALS

Findings

DISCUSSION