Vertical niche differentiation of ectomycorrhizal hyphae in soil as shown by T‐RFLP analysis

Abstract

Summary• Niche differentiation for different soil substrates has been proposed as a mechanism contributing to ectomycorrhizal fungal diversity. This hypothesis has been largely untestable because of a lack of techniques to study the in situ distribution of ectomycorrhizal hyphae.• We developed a technique involving soil DNA extraction, PCR and terminal restriction fragment length polymorphism (T-RFLP) analysis for species identification to investigate the vertical distribution of fungal hyphae in four distinct layers of the forest floor (lower litter, F-layer, H-layer, and B-horizon) of a Pinus resinosa plantation.• Fungal communities differed markedly among the four layers. Cluster analysis suggested six different patterns of resource utilization: litter-layer specialists, litterlayer generalists, F-layer, H-layer, and B-horizon species, and multilayer generalists. Known ectomycorrhizal species were found in all six clusters.• This spatial partitioning observed among ectomycorrhizal fungi along a single, relatively simple substrate-resource gradient supports the niche differentiation hypothesis as an important mechanism contributing to ectomycorrhizal fungal diversity.

Diversity of an ectomycorrhizal fungal community studied by a root tip and total soil DNA approach

“…However, Russula sp. and Lactarius sp., both having smooth hyphal mantles and lacking large amounts of emanating hyphae (Agerer 2001), have been detected in several molecular studies on soil fungal diversity (Chen and Cairney 2002;Dickie et al 2002;Landeweert et al 2003;Smit et al 2003).…”

“…In contrast to the detection of fungal pathogens, accurate detection of EM mycelium in soil involves total removal of (fragments of) EM root tips. Separation of root tips from soil samples is often done by sieving the samples (Guidot et al 2002;Landeweert et al 2003) or by the removal of root tips with a pair of forceps under a dissecting microscope (Chen and Cairney 2002;Dickie et al 2002;Landeweert et al 2003). In some cases complete hyphal strands and mycelium have been extracted from soil (Zhou et al 2001;H.…”

“…Sampling of EM root tips is typically inadequate when attempting to obtain a true picture of species richness (Horton and Bruns 2001) and the use of soil DNA extracts can reduce several sample biases related to root tip sampling. The use of molecular identification methods to study EM hyphae in soil will become more common in the near future, as these techniques permit in situ testing of hypotheses on resource partitioning and niche differentiation of individual fungi (Dickie et al 2002). Methods based on soil DNA extracts might be a good alternative when analysing species diversity of an EM fungal community, but it depends on the nature of the study whether the answers needed are best provided by a root tip or mycelial approach.…”

“…Recently, molecular methods based on total soil DNA extracts were used to detect and identify EM mycelium in natural soil (Chen and Cairney 2002;Dickie et al 2002;Landeweert et al 2003). These molecular methods enable the identification of fungi in soil without the extraction or cultivation of the organisms themselves.…”

“…In addition, the method used to extract root tips from the soil that will be used to detect mycelium should be chosen after careful consideration. Other studies have removed root tips from soil samples by visually checking for the presence of root tips under the dissecting microscope or by sieving the soil before extracting total soil DNA (Chen and Cairney 2002;Dickie et al 2002;Landeweert et al 2003). Several sieve mesh sizes have been used to separate soil from EM root tips but it is unknown whether and how these different sieve mesh sizes influence the outcome of the study.…”