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.

Marketa Stepanova et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-827', Anonymous Referee #1, 27 Jul 2023
  • RC2: 'Comment on egusphere-2023-827', Anonymous Referee #2, 27 Jul 2023

Marketa Stepanova et al.

Marketa Stepanova et al.


Total article views: 273 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
216 37 20 273 28 8 8
  • HTML: 216
  • PDF: 37
  • XML: 20
  • Total: 273
  • Supplement: 28
  • BibTeX: 8
  • EndNote: 8
Views and downloads (calculated since 21 Jun 2023)
Cumulative views and downloads (calculated since 21 Jun 2023)

Viewed (geographical distribution)

Total article views: 264 (including HTML, PDF, and XML) Thereof 264 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 03 Oct 2023
Short summary
Biological N2-fixation helps to sustain carbon accumulation in peatlands and to remove CO2 from the atmosphere. Changes in N2-fixation may affect the dynamics of global change. Increasing inputs of reactive N from air pollution should lead to downregulation of N2-fixation. Data from three N-polluted peat bogs show an interplay of N2-fixation rates with 10 potential drivers of this process. N2-fixation was measurable only at one site characterized by high phosphorus and low sulfate availability.