page_title: Ectomycorrhizal extramatrical mycelium
section_title: Carbon cycling
hierarchical_section_title: Ectomycorrhizal extramatrical mycelium / Ecological implications / Carbon cycling
caption_attribution_description: Douglas-fir Pseudotsuga menziesii subsp. menziesii root with Cortinarius sp. ectomycorrhizae. Corvallis, Oregon.
context_page_description: Ectomycorrhizal extramatrical mycelium is the collection of filamentous fungal hyphae emanating from ectomycorrhizas. It may be composed of fine, hydrophilic hypha which branches frequently to explore and exploit the soil matrix or may aggregate to form rhizomorphs; highly differentiated, hydrophobic, enduring, transport structures.
context_section_description: Although there is evidence that certain species of mycorrhizal fungi may obtain at least a portion of their carbon via saprotrophic nutrition, the bulk of mycorrhizal carbon acquisition happens by way of trading for host-derived photosynthetic products. Mycorrhizal systems represent a major carbon sink. Laboratory studies predict that around 23% of plant-derived carbon is allocated to extrametrical mycelium, although an estimated 15-30% of this is lost to fungal respiration.
  Carbon allocation is distributed unequally to extramatrical mycelium depending on fungal taxa, nutrient availability, and the age of the associated mycorrhizas. Much of the carbon allocated to extramatrical mycelium accumulates as fungal biomass, making up an estimated one-third of the total microbial biomass and one-half of the total dissolved organic carbon in some forest soils. Carbon also supports the production of sporocarps and sclerotia, with various taxa investing differentially in these structures rather than in the proliferation of extramatrical mycelium. Carbon acquisition also goes toward the production of fungal exudates. Extramatrical hyphae excrete a range of compounds into the soil matrix, accounting for as much as 40% of total carbon usage. These exudates are released primarily at the growing front, and are used in functions such as mineralization and homeostasis.
  
  Many researchers have attempted projections of the role that extramatrical mycelium may play in carbon sequestration.  Although estimates of the life span of individual ectomycorrhizas very considerably, turnover is generally considered on a scale of months. 
  After death, the presence ectomycorrhizas on root tips, may increase the rate of root decomposition for some fungal taxa. Besides host plant death and mycorrhizal turnover, rates of carbon sequestration may also be affected by disturbances in the soil, which cause sections of the extramatrical mycelium to become severed from the host plant. Such disturbances, such as those caused by animal disruption, mycophagous invertebrates or habitat destruction, may have a notable impact on turnover rates. These variables make it difficult to estimate the turnover rates of mycorrhizal biomass in forest soils and the relative contribution of extramatrical mycelium to carbon sequestration.
caption: Cortinarius ectomycorrhizas and extramatrical mycelium on Pseudotsuga menziesii roots
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