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https://doi.org/10.5194/egusphere-2023-827
https://doi.org/10.5194/egusphere-2023-827
21 Jun 2023
 | 21 Jun 2023

Contrasting potential for biological N2-fixation at three polluted Central European Sphagnum peat bogs: Combining the 15N2-tracer and natural-abundance isotope approaches

Marketa Stepanova, Martin Novak, Bohuslava Cejkova, Ivana Jackova, Frantisek Buzek, Frantisek Veselovsky, Jan Curik, Eva Prechova, Arnost Komarek, and Leona Bohdalkova

Abstract. Availability of reactive nitrogen (Nr) is a key control of carbon (C) sequestration in wetlands. To complement the metabolic demands of Sphagnum in pristine rain-fed bogs, diazotrophs supply additional Nr via biological nitrogen fixation (BNF). Since breaking the triple bond of atmospheric N2 is energy-intensive, it is reasonable to assume that increasing inputs of pollutant Nr will lead to BNF downregulation. Yet, recent studies have documented measurable BNF rates in Sphagnum-dominated bogs also in polluted regions, indicating adaptation of N2-fixers to changing N deposition. Our aim was to quantify BNF at high-elevation peatlands located in industrialized Central Europe. A 15N2-tracer experiment was combined with a natural-abundance N-isotope study at three Sphagnum-dominated peat bogs in the northern Czech in an attempt to assess the roles of individual BNF drivers. High short-term BNF rates (8.2 ± 4.6 g N m2 d−1) were observed at Male Mechove Jezirko receiving ~17 kg Nr ha−1 yr−1. The remaining two peat bogs, whose recent atmospheric Nr inputs differed from Male Mechove Jezirko only by 1–2 kg ha−1 yr−1 (Uhlirska and Brumiste), showed zero BNF. The following parameters were investigated to elucidate the BNF difference: NH4+-N/NO3-N ratio, temperature, wetness, Sphagnum species, organic-N availability, possible P limitation, possible Mo limitation, SO42− deposition, and pH. At Male Mechove Jezirko and Uhlirska, the same moss species (S. girgensohnii) was used for the 15N2 experiment, and therefore host identity could not explain the difference in BNF at these sites. Temperature and moisture were also identical in all incubations and could not explain the between-site differences in BNF. The N:P stoichiometry in peat and bog water indicated that Brumiste may have lacked BNF due to P limitation, whereas non-detectable BNF at Uhlirska may have been related to 70 times higher SO42− concentration in bog water. Across the sites, the mean natural-abundance δ15N values increased in the order: atmospheric deposition (−5.3 ± 0.3 ‰) < Sphagnum (−4.3 ± 0.1 ‰) < bog water (−3.9 ± 0.4 ‰) < atmospheric N2 (0.0 ‰). Only at Brumiste, N in Sphagnum was significantly isotopically heavier than in atmospheric deposition, possibly indicating a longer-term BNF effect. Collectively, our data highlight spatial heterogeneity in BNF rates under high Nr inputs and the importance of environmental parameters other than atmospheric Nr pollution in regulating BNF.

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Journal article(s) based on this preprint

22 Dec 2023
Contrasting potential for biological N2 fixation at three polluted central European Sphagnum peat bogs: combining the 15N2-tracer and natural-abundance isotope approaches
Marketa Stepanova, Martin Novak, Bohuslava Cejkova, Ivana Jackova, Frantisek Buzek, Frantisek Veselovsky, Jan Curik, Eva Prechova, Arnost Komarek, and Leona Bohdalkova
SOIL, 9, 623–640, https://doi.org/10.5194/soil-9-623-2023,https://doi.org/10.5194/soil-9-623-2023, 2023
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

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Biological N2-fixation helps to sustain carbon accumulation in peatlands and to remove CO2 from...
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