Ectomycorrhiza functioning in young and mature forest stands

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As many as 15,000 species of fungi form symbiotic associations called ectomycorrhizas with roots of woody plants. One reason that there are so many ectomycorrhizal fungi may be because they fill specific niches in the soil. New methods in molecular biology have demonstrated that the hyphae of different ectomycorrhizal fungi are indeed found in different soil horizons or microsites. In addition, the extramatrical hyphae (those that extend well beyond the root) may be located in a different part of the soil profile from roots colonized by that fungus. However we know almost nothing about how the physiologies of these fungi relate to distribution amongst microsites. My research group uses several approaches to study the role of ectomycorrhizal fungi in nutrient uptake and nutrient cycling in the field. It is important to study ectomycorrhizal physiology in situ, where possible, so that bacteria associated with hyphae are native ones, and so that the extensive network of hyphae formed by these associations can remain intact. We will use a root window-based imprinting technique to identify mm-scale 'hot spots' of extracellular enzyme activity. These enzymes are involved in organic matter breakdown. Using the imprints as a guide, we will collect very small soil samples, from which we will amplify fungal DNA. We will then determine whether fungal communities in the hot spots differed from those in microsites with low enzyme activities. At some sites, we will test whether ectomycorrhizal fungi that are more common in decayed wood are more likely to secrete enzymes that break down lignin and cellulose found in wood. We will do this both by measuring the activities directly, as well as by detecting soil mRNA for these enzymes. We will also use stable isotopes of nitrogen as tracers to determine whether fungi that dominate clearcut communities differ in their ability to absorb organic N from fungi found in forests with well-developed forest floors. Much of the variation in soil microbial communities is "still viewed as random noise". Our research will help to determine whether physiological differences amongst ectomycorrhizal fungi is one of the factors that influences their distribution.