A survey of micorrhizal infection in an amazonian rain forest

Abstract

A survey of mycorrhizal infectlon and depth of rootlets was carried out on a hectare of primary rain forest in w hich ali individuais over 15 em in diameter had been iàentified and labeled . Non·mycorrhiza!. lightly infected, moderately infected, and heavily infected species made up 16. 7, 23.2, 14.8, and 16. 7% , respec· tively, of tha total plot's ecological importance value. Of the plot's t:>tal importance value. 59 .9% were found to have fine roots in the 0-to 10·cm depth ra nge, 7% to be in the 10·to 30-cm range, and 7 . 9% to have roots deeper tha,, 30 em . A strong association was found between root depth and mycorrhizal condition, with surface roo ts much more llkely to be infected than deep roots. Root let depth was shown to be a consistent trait with:n a species and most often w ithin a genus. The deep-rooted, non-mycorrhizal condition was interpreted as an ecological "strategy" for avoiding competition w it:1 more efficien t mycorrhizal species . . INTRODUCTIONIn 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 rema in scarce . The nearest approach to this kind of information is in various su rveys of tropical habitats: lists of species, including some natives (Janse, 1897); Johnson, 1949; Redhead, 1968); a short list of natives (Edmisten, 1970); or a determination based on unidentified root fragments (Stark, 1970) . Only the last report allows the overall amundance of infection to be assessed , and its data apparently refer only to surface roots. 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 T . V. St . John (" ) 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. Each sampled speci es was assigneo to one of four classes of infection by a semi· quantitative evaluation of intensity of infection. Finally, the depth at which each root sample was recovered was recorded . METHODS AND MATERIALS IMPORTANCE VALUE Phytosociological dat a from Prance et a/.( 1976) were used t ogenerate an index of importance value for each species on the plot. We modified the importance value index of Curtis & Mclntosh (1950) to exclude a measure of frequency . 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. Our index was converted to an importance percentage value as clone by Risser & Rice ( 1971) Ou r index was (N + BA ) / 2. where N i i i is the fraction of the total number of individuais comprised by spec...

Arbuscular mycorrhizal colonization of vascular plants from the Yungas forests, Argentina

“…Bearing in mind that this study does not exclude the possibility of the occurrence of other kinds of mycorrhizal associations in the species examined, an absolute dominance of AM was observed in these plants. These results are in agreement with Janos' [52] and other authors' observations on the mycorrhizal status of neotropical forests [12,77].…”

“…Attention has been focused on the mycorrhizas of forests in the humid tropics [11,12,50,51,60,72,73,77], but there is little information concerning the distribution and abundance of these types of symbioses in the Yungas [3][4][5][6][7][8]. Little is known of this endangered ecosystem and an urgent call is made for its conservation.…”

Variation of the Linkage of Root Function with Root Branch Order

“…This can be the case for P. baillonii , which has the coarse, little-branched and hairless ‘magnolioid roots’ [8], [10], [40]. In this type of root, nutrient uptake depends primarily on mycorrhizal fungi [8], [9]. This can be supported by the high MC rate (Table 2) and extent as indicated by the thicker cortex that can host more mycorrhizal fungi [1], [36] in P. baillonii .…”

“…The great root trait variation in these ecosystems has the potential to result in a different linkage of root function with root branch order. For example, in an early study, Baylis noted that many tree species in Magnoliales (distributed mainly in tropics and subtropics) had coarse, little-branched and hairless terminal roots and named it ‘magnolioid roots’ [8], [9]. Species with this type of roots depend primarily on mycorrhizal fungi for nutrient uptake [8],[10].…”

Dispersion, an Important Radiation Mechanism for Ectomycorrhizal Fungi in Neotropical Lowland Forests?

“…Inocybe is often mentioned in the literature as a pioneer and an effective coloniser by spore dispersal (Smith and Read, 2008). Although they are often scattered in AM dominated forests (Béreau et al, 1997;Lodge, 1987;Singer & Araujo, 1979;St John, 1980;Tedersoo et al, 2010a), species belonging to confirmed EcM tree hosts are diverse and widely distributed in the Guayana region (Table 1). These nondominant Neotropical EcM plants might have contributed to the dispersion of EcM fungal groups such as Inocybe subgenus Inocybe by co-migration (Halling, 2001) or by providing "EcM tree islands" for fungus colonization (Peay et al, 2007).…”