The stable carbon isotope signature of methane produced by saprotrophic fungi

Schroll, Moritz; Keppler, Frank; Greule, Markus; Eckhardt, Christian; Zorn, Holger; Lenhart, Katharina

Methane (inline-formulaCH4) is the most abundant organic compound in the atmosphere and is emitted from many biotic and abiotic sources. Recent studies have shown that inline-formulaCH4 production occurs under aerobic conditions in eukaryotes, such as plants, animals, algae, and saprotrophic fungi. Saprotrophic fungi play an important role in nutrient recycling in terrestrial ecosystems via the decomposition of plant litter. Although inline-formulaCH4 production by saprotrophic fungi has been reported, no data on the stable carbon isotope values of the emitted inline-formulaCH4 (inline-formulaδ13C-inline-formulaCH4 values) are currently available. In this study, we measured the inline-formulaδ13C values of inline-formulaCH4 and carbon dioxide (inline-formulaδ13C-inline-formulaCO2 values) emitted by two saprotrophic fungi, Pleurotus sapidus (oyster mushroom) and Laetiporus sulphureus (sulphur shelf), cultivated on three different substrates, pine wood (Pinus sylvestris), grass (mixture of Lolium perenne, Poa pratensis, and Festuca rubra), and corn (Zea mays), which reflect both inline-formulaC3 and inline-formulaC4 plants with distinguished bulk inline-formulaδ13C values. Applying Keeling plots, we found that the inline-formulaδ13C source values of inline-formulaCH4 emitted from fungi cover a wide range from inline-formula−40 to inline-formula−69 mUr depending on the growth substrate and fungal species. Whilst little apparent carbon isotopic fractionation (in the range from inline-formula−0.3 to 4.6 mUr) was calculated for the inline-formulaδ13C values of inline-formulaCO2 released from P. sapidus and L. sulphureus relative to the bulk inline-formulaδ13C values of the growth substrates, much larger carbon isotopic fractionations (ranging from inline-formula−22 to inline-formula−42 mUr) were observed for the formation of inline-formulaCH4. Although the two fungal species showed similar inline-formulaδ13CH4 source values when grown on pine wood, inline-formulaδ13CH4 source values differed substantially between the two fungal species when they were grown on grass or corn. We found that the source values of inline-formulaδ13CH4 emitted by saprotrophic fungi are highly dependent on the fungal species and the metabolized substrate. The source values of inline-formulaδ13CH4 cover a broad range and overlap with values reported for methanogenic archaea, the thermogenic degradation of organic matter, and other eukaryotes.

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Schroll, Moritz / Keppler, Frank / Greule, Markus / et al: The stable carbon isotope signature of methane produced by saprotrophic fungi. 2020. Copernicus Publications.

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