Rhizosphere interactions: the root microbiome
Jones , Melanie Dawn .
Does ectomycorrhizal fungal diversity contribute to functional diversity in the ectomycorrhizosphere?
Ectomycorrhizal fungal biomass typically comprises 25-40% of the biomass of ectomycorrhizal root tips and, thus, dominates the microbiota of these roots. As is characteristic of fungi in general, ECM fungi carry out absorptive nutrition. They excrete enzymes that degrade complex biopolymers into monomers that can be absorbed by themselves, other microbes, or roots. This is one of the ways in which ectomycorrhizal fungi influence nutrient availability in soil. Recently, methods for quantifying soil enzyme activities in micro-well plates have been modified to allow the assay of individual ectomycorrhizasin order to investigate the influence of the ectomycorrhizal fungal symbiont on enzyme activities in the rhizosphere. We typically measure the activities of N-acetylglucosaminidase, sulfatase, phosphomonoesterase, cellobiohydrolase, beta-glucosidase, xylosidase, leucine amino peptidase and laccase. These are an array of exoenzymes involvedin either breaking down cell wall components to provide access to nutrient-rich materials within cells or in releasing N, S or P from macromolecules in absorbable forms. Given that the mycorrhizas are collected from the field, the enzymes assayed could be produced either by the fungi themselves or by prokaryotes associated with fungal or root surfaces. I will present the results of studies conducted in early successional systems following wildfire or clearcutting, as well as pine and spruce stands perturbed by long-term addition of balanced fertilizer. We detected evidence of functional overlap among ectomycorrhizal fungi in terms of their enzyme profiles. Although activities of many of the exoenzymes were higher in systems with higher soil carbon or total N, identity of the fungal symbiont was the most important factor influencing the enzyme profile of any individual ectomycorrhiza. In systems where there was a substantial change in the ectomycorrhizal fungal community on roots (e.g.,between seedlings from clearcuts vs. adjacent forests), the enzyme profiles also differed substantially. We conclude that by associating with a range of ectomycorrhizal fungi, a host tree or seedling increases functional diversity with respect to uptake of nutrients from organic sources.
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Presentation Type: Symposium or Colloquium Presentation
Location: Delaware D/Hyatt
Date: Tuesday, July 10th, 2012
Time: 9:15 AM