The stable carbon isotope signature of methane produced by saprotrophic fungi

<p>Methane (<span class="inline-formula">CH<sub>4</sub></span>) is the most abundant organic compound in the atmosphere and is emitted from many biotic and abiotic sources. Recent studies have shown that <span class="inline-formula">CH<sub&g...

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Bibliographic Details
Main Authors: M. Schroll, F. Keppler, M. Greule, C. Eckhardt, H. Zorn, K. Lenhart
Format: Article
Language:English
Published: Copernicus Publications 2020-07-01
Series:Biogeosciences
Online Access:https://bg.copernicus.org/articles/17/3891/2020/bg-17-3891-2020.pdf
Description
Summary:<p>Methane (<span class="inline-formula">CH<sub>4</sub></span>) is the most abundant organic compound in the atmosphere and is emitted from many biotic and abiotic sources. Recent studies have shown that <span class="inline-formula">CH<sub>4</sub></span> 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 <span class="inline-formula">CH<sub>4</sub></span> production by saprotrophic fungi has been reported, no data on the stable carbon isotope values of the emitted <span class="inline-formula">CH<sub>4</sub></span> (<span class="inline-formula"><i>δ</i><sup>13</sup>C</span>-<span class="inline-formula">CH<sub>4</sub></span> values) are currently available. In this study, we measured the <span class="inline-formula"><i>δ</i><sup>13</sup>C</span> values of <span class="inline-formula">CH<sub>4</sub></span> and carbon dioxide (<span class="inline-formula"><i>δ</i><sup>13</sup>C</span>-<span class="inline-formula">CO<sub>2</sub></span> values) emitted by two saprotrophic fungi, <i>Pleurotus sapidus</i> (oyster mushroom) and <i>Laetiporus sulphureus</i> (sulphur shelf), cultivated on three different substrates, pine wood (<i>Pinus sylvestris</i>), grass (mixture of <i>Lolium perenne</i>, <i>Poa pratensis</i>, and <i>Festuca rubra</i>), and corn (<i>Zea mays</i>), which reflect both <span class="inline-formula">C<sub>3</sub></span> and <span class="inline-formula">C<sub>4</sub></span> plants with distinguished bulk <span class="inline-formula"><i>δ</i><sup>13</sup>C</span> values. Applying Keeling plots, we found that the <span class="inline-formula"><i>δ</i><sup>13</sup>C</span> source values of <span class="inline-formula">CH<sub>4</sub></span> emitted from fungi cover a wide range from <span class="inline-formula">−40</span> to <span class="inline-formula">−69</span>&thinsp;mUr depending on the growth substrate and fungal species. Whilst little apparent carbon isotopic fractionation (in the range from <span class="inline-formula">−0.3</span> to 4.6&thinsp;mUr) was calculated for the <span class="inline-formula"><i>δ</i><sup>13</sup>C</span> values of <span class="inline-formula">CO<sub>2</sub></span> released from <i>P. sapidus</i> and <i>L. sulphureus</i> relative to the bulk <span class="inline-formula"><i>δ</i><sup>13</sup>C</span> values of the growth substrates, much larger carbon isotopic fractionations (ranging from <span class="inline-formula">−22</span> to <span class="inline-formula">−42</span>&thinsp;mUr) were observed for the formation of <span class="inline-formula">CH<sub>4</sub></span>. Although the two fungal species showed similar <span class="inline-formula"><i>δ</i><sup>13</sup>CH<sub>4</sub></span> source values when grown on pine wood, <span class="inline-formula"><i>δ</i><sup>13</sup>CH<sub>4</sub></span> source values differed substantially between the two fungal species when they were grown on grass or corn. We found that the source values of <span class="inline-formula"><i>δ</i><sup>13</sup>CH<sub>4</sub></span> emitted by saprotrophic fungi are highly dependent on the fungal species and the metabolized substrate. The source values of <span class="inline-formula"><i>δ</i><sup>13</sup>CH<sub>4</sub></span> cover a broad range and overlap with values reported for methanogenic archaea, the thermogenic degradation of organic matter, and other eukaryotes.</p>
ISSN:1726-4170
1726-4189