Diversity and function of fungi in peatlands: A carbon cycling perspective

Abstract

Thormann, M. N. 2006. Diversity and function of fungi in peatlands: A carbon cycling perspective. Can. J. Soil Sci. 86: 281-293. Peatlands are a dominant landform in the northern hemisphere, accumulating carbon in the form of peat due to an imbalance between decomposition and plant production rates. Decomposer (saprobes) and mycorrhizal fungi significantly influence carbon dynamics by degrading organic matter via the synthesis of extracellular enzymes. As organic matter decomposes, litter quality variables figure most prominently in the succession of fungi. Hence, litters composed primarily of complex polymers decompose very slowly. Surprisingly, recalcitrant polymer degraders (mostly basidiomycetes) are rarely isolated from peat, which may explain the accumulation of complex polymers in peat profiles. While enzymatic profiles of mycorrhizal fungi and other root endophytes may be more limited compared with saprobes, many of these fungi can degrade polymers of varying complexity as well and hence may also be significant decomposers of organic matter. To date, anamorphic ascomycetes and zygomycetes are the most frequently isolated fungi from peatlands (63 and 10% of all taxa, respectively), and chytridiomycetes, teleomorphic ascomycetes, and basidiomycetes appear to be less common (11% of all taxa). The remaining 16% of taxa remain unidentified or are sterile taxa. How disturbances affect peatland microbial communities and their roles is virtually unknown. This aspect of peatland microbial ecology requires immediate attention. The objective of this paper is to review the current state of knowledge of the diversity of fungi and their roles in carbon cycling dynamics in peatlands. Can. J. Soil Sci. 86: 281-293. Les tourbières figurent parmi les principales formes de relief dans l'hémisphère nord. Elles accumulent du carbone sous la forme de tourbe, produit du déséquilibre entre le taux de décomposition et le taux de production des végétaux. Les microorganismes décomposeurs (saprobiontes) et les champignons des mycorhizes ont une action considérable sur la dynamique du carbone, car ils dégradent la matière organique par la synthèse d'enzymes extracellulaires. Lorsque la matière organique se décompose, ce sont les paramètres qualitatifs des détritus végétaux qui commandent le plus la succession de champignons. C'est pourquoi les débris essentiellement composés de polymères complexes se décomposent très lentement. Pourtant, il est surprenant qu'on isole si rarement les saprobiontes des polymères récalcitrants (surtout des basidiomycètes) de la tourbe, ce qui expliquerait l'accumulation de polymères complexes dans cette dernière. Bien que le profil enzymatique des champignons des mycorhizes et d'autres endophytes des racines soit plus étroit que celui des saprobiontes, bon nombre de ces champignons dégradent aussi des polymères de complexité variable. Ils pourraient donc être d'importants décomposeurs de la matière organique. Jusqu'à présent, les champignons qu'on retrouve le plus souvent dans les tourbières sont des a...

Microbial Community Structure and Activity Linked to Contrasting Biogeochemical Gradients in Bog and Fen Environments of the Glacial Lake Agassiz Peatland

“…This finding is contrary to prior cultivation-dependent studies, which suggested that surface peatlands with extensive hyphal growth are usually dominated by fungal biomass (29,72). Our qPCR values simply represent ratios of fungal/bacterial SSU gene abundance, instead of biomass.…”

Aerobic carbon-cycle related microbial communities in boreal peatlands: responses to water-level drawdown

“…Quite unexpectedly, sequences similar to the common and fast growing genera Mucor and Penicillium were not detected at any of our sites (II, IV, V) even though their presence in peatlands has been confirmed elsewhere (e.g., Given and Dickinson 1975, Thormann 2006a, 2006b. It is unlikely that these genera would be entirely absent from Lakkasuo and Suonukkasuo, but they are certainly not abundant (II).…”

“…Cellulose-degrading fungi are more abundant in peatlands than their bacterial counterparts (Hiroki and Watanabe 1996) and nowadays fungi are considered to be the main aerobic decomposers in these habitats (e.g., Thormann 2006aThormann , 2006b). In pristine wet peatlands, fungal decomposers are mostly limited to the uppermost surface layers (Latter et al 1967, Nilsson andRülcker 1992).…”

“…Many microfungal species have been isolated from living and decomposing Sphagnum fuscum, and their ability to decompose various organic compounds, e.g., tannic acids, cellulose and pectine, is well described (Thormann et al 2001(Thormann et al , 2002. From a taxonomic point of view, anamorphic ascomycetes were the largest group (62%) of microfungi and genera Penicillium and Acremonium were the dominant groups in peatland isolation studies (Thormann 2006a). Zygomycetes (Mortierella) were also frequently isolated (10% of all species).…”

Litter type affects the activity of aerobic decomposers in a boreal peatland more than site nutrient and water table regimes

“…Indirect effects of WT drawdown on the composition and activity of aerobic microbial decomposers in peatlands via changes in plant community structure are, in spite of their significance, still poorly understood (Laiho, 2006;Thormann, 2006). Furthermore, soil nutrient availability may influence community-level decomposition processes (Hobbie and Gough, 2004).…”