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Can isotopic fractionation during respiration explain the 13C-enriched sporocarps of ectomycorrhizal and saprotrophic fungi?
Örebro University, Department of Natural Sciences.
Örebro University, Department of Natural Sciences.
Örebro University, Department of Natural Sciences.ORCID iD: 0000-0003-4384-5014
2008 (English)In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 177, no 4, p. 1012-1019Article in journal (Refereed) Published
Abstract [en]

• The mechanism behind the 13C enrichment of fungi relative to plant materials is unclear and constrains the use of stable isotopes in studies of the carbon cycle in soils.

• Here, we examined whether isotopic fractionation during respiration contributes to this pattern by comparing δ13C signatures of respired CO2, sporocarps and their associated plant materials, from 16 species of ectomycorrhizal or saprotrophic fungi collected in a Norway spruce forest.

• The isotopic composition of respired CO2 and sporocarps was positively correlated. The differences in δ13C between CO2 and sporocarps were generally small, < ±1‰ in nine out of 16 species, and the average shift for all investigated species was 0.04‰. However, when fungal groups were analysed separately, three out of six species of ectomycorrhizal basidiomycetes respired 13C-enriched CO2 (up to 1.6‰), whereas three out of five species of polypores respired 13C-depleted CO2 (up to 1.7‰; P < 0.05). The CO2 and sporocarps were always 13C-enriched compared with wood, litter or roots.

• Loss of 13C-depleted CO2 may have enriched some species in 13C. However, that the CO2 was consistently 13C-enriched compared with plant materials implies that other processes must be found to explain the consistent 13C-enrichment of fungal biomass compared with plant materials.

Place, publisher, year, edition, pages
Cambridge: Cambridge University Press , 2008. Vol. 177, no 4, p. 1012-1019
Keywords [en]
Carbon/*metabolism, Carbon Dioxide/metabolism, Carbon Isotopes, Fungi/*metabolism, Nitrogen/metabolism, Nitrogen Isotopes, Oxygen Consumption/*physiology, Picea/microbiology, Time Factors, Trees/microbiology
National Category
Ecology Soil Science Natural Sciences Agricultural Sciences
Research subject
biologi
Identifiers
URN: urn:nbn:se:oru:diva-4647DOI: 10.1111/j.1469-8137.2007.02332.xPubMedID: 18086229OAI: oai:DiVA.org:oru-4647DiVA, id: diva2:138946
Available from: 2008-10-20 Created: 2008-10-20 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Achieving carbon isotope mass balance in northern forest soils, soil respiration and fungi
Open this publication in new window or tab >>Achieving carbon isotope mass balance in northern forest soils, soil respiration and fungi
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Northern forests contain a large part of the global terrestrial carbon pool and it is unclear whether they will be sinks or sources for atmospheric carbon if the climate warms as predicted. Stable isotope techniques provide unique tools to study the carbon cycle at different scales but the interpretation of the isotope data is impaired by our inability to close the carbon isotope mass balance of ecosystems. This involves the paradox that the soil organic matter becomes increasingly 13C-enriched with increasing soil depth relative to the carbon input, plant litter, at the same time as soil respiration, the major carbon outflow from the soil, and fungi, organisms dependent on plant derived carbon, both are relatively 13C-enriched. I have determined the δ13C of the respired CO2 and the organic matter from different ecosystem components in a Norway spruce forest aiming at finding an explanation to the observed carbon isotope pattern.

In the first study the soil surface respiration rate and isotopic composition was found to be governed by aboveground weather conditions the preceding 1-6 days. This suggests there is a fast flux of recent photosynthates to root respiration. In the second study I compared the respired CO2 from decomposition with the δ13C of the root free soil organic matter sampled from the litter layer down to 50 cm depth. Discrimination against 13C during respiration could not explain the 13C enrichment of soil organic matter with depth because the δ13C of the respired CO2 became increasingly 13C-enriched relative to the organic matter with soil depth. However, ~1.5‰ of the 2‰ 13C-gradient could be explained by the 13C depletion of atmospheric CO2 that has proceeded since the beginning of the 18th century due to the burning of fossil fuels and deforestation. The remaining shift was hypothesized to be due to a belowground contribution of 13C-enriched ectomycorrhizal derived carbon. In the third study I compared the δ13C of respired CO2 and sporocarps of ectomycorrhizal and saprotrophic fungi sampled in the spruce forest. The δ13C of respired CO2 and sporocarps were positively correlated and the differences in δ13C between CO2 and sporocarps were small, <±1‰ in nine out of 16 species, although three out of six species of ectomycorrhizal basidiomycetes respired 13C-enriched CO2 (up to 1.6‰), whereas three out of five species of polypores respired 13C-depleted CO2 (up to 1.7‰; P<0.05). Loss of 13C-depleted CO2 may have enriched the biomass of some fungal species in 13C. However, the consistent 13C enrichment of fungal sporocarps and respired CO2 relative to the plant materials implies that other processes must be found to explain the consistent 13C-enrichment of fungal biomass compared to plant materials. In the final study, compound specific stable isotope analyses provided further evidence for the hypothesis that the biomass of ectomycorrhizal fungi are 13C-enriched relative to host biomass because the carbon provided by the host is 13C-enriched Furthermore, ectomycorrhizal fungi showed lower average δ13C values of metabolites than saprotrophs which gives further support for the so-called saprotrophic-mycorrhizal divide. I conclude that a belowground allocation of 13C-enriched carbon to ectomycorrhizal fungi closes the carbon isotope mass balance in boreal and temperate forest soils and explains the 13C-enriched soil respiration.

Place, publisher, year, edition, pages
Örebro: Örebro universitet, 2008. p. 60
Series
Örebro Studies in Biology, ISSN 1650-8793 ; 5
Keywords
13C, Carbon cycle, Ectomycorrhizal fungi, Forest soil, Microbial respiration, Soil respiration, Stable isotopes
National Category
Biological Sciences
Research subject
Biology
Identifiers
urn:nbn:se:oru:diva-2101 (URN)978-91-7668-594-5 (ISBN)
Public defence
2008-05-23, Hörsal T, Teknik, Örebro universitet, Örebro, 10:00
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Supervisors
Available from: 2008-04-24 Created: 2008-04-24 Last updated: 2017-10-18Bibliographically approved

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Boström, BjörnComstedt, DanielEkblad, Alf

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