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Sphagnum and feather moss-associated N2 fixation along a 724-year chronosequence in eastern boreal Canada

Abstract

Dinitrogen (N2) fixation associated with moss-dwelling bacteria (diazotrophs) is a N source in boreal forests. In feather moss-dominated understories of Fennoscandia, N2 fixation rates increase with forest age due to N limitation. Whether this is applicable across different boreal ecosystems and successional pathways is not fully understood. In eastern Canada, increasing Sphagnum dominance starting about 100 years post-fire (paludification), is prevalent. Our main objectives were to determine how potential moss-associated N2 fixation and relative contributions of Sphagnum and other mosses vary with time since fire and to explore the mechanisms driving observed patterns. Sampling was conducted in eight black spruce forests (Picea mariana; 64–724 years post-fire) in northwestern Quebec, Canada, along an established post-fire successional gradient. Potential N2 fixation was measured with the acetylene reduction method in seven common moss species (Pleurozium schreberi, Hylocomium splendens, Dicranum polysetum, Sphagnum capillifolium, Sphagnum angustifolium, Sphagnum russowii, and Sphagnum magellanicum). N2 fixation rates by moss communities were low and seemed to increase with stand age, but large variability was found between sites and species. The mechanisms underlying N2 fixation rates were related to a switch in moss communities from feather moss to a Sphagnum dominance, which had the highest individual acetylene reduction rates, and to an increasing frequency of N2-fixing samples in old forests. This study provided one of the first records of moss-associated N2 fixation in eastern Canada and offers insights into how regional and cross-continental differences in moss community composition determine N cycling in boreal forests.

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Data availability

Upon acceptance of the manuscript, all data (acetylene reduction rates and environmental data) will be submitted to the DRYAD online database (https://datadryad.org/stash). Moss tissue percent carbon and nitrogen are provided in Supplementary Information 1.

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Acknowledgements

This project would not have been possible without the funding provided by the NSERC-UQAT-UQAM Chair in Sustainable Forest Management in Québec, Canada. Morgane Higelin, Christine Allen, Jeffrey Opoku-Nyame, and Andréane Garant helped with field work, while Kelley Gundale helped with acetylene reduction analyses in the lab.

Funding

This project was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) Chair in Sustainable Forest Management in Québec at Université du Québec en Abitibi-Témiscamingue and Université du Québec à Montréal.

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Contributions

NJF, M-CN, and YB contributed to the study conception and design. NJF and M-CN completed data collection and laboratory analyses. MJ conducted data analysis and drafted the manuscript. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Mélanie Jean.

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The authors declare no conflict of interest or competing interests.

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Communicated by Dafeng Hui.

Supplementary Information

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Supplementary file1 (DOCX 87 kb)

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Jean, M., Fenton, N.J., Bergeron, Y. et al. Sphagnum and feather moss-associated N2 fixation along a 724-year chronosequence in eastern boreal Canada. Plant Ecol 222, 1007–1022 (2021). https://doi.org/10.1007/s11258-021-01157-x

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  • DOI: https://doi.org/10.1007/s11258-021-01157-x

Keywords

  • Nitrogen fixation
  • Boreal forest
  • Feather moss
  • Sphagnum
  • Paludification