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<p>In northern biomes, growth is nitrogen (N) limited, but bryophytes are abundant. These bryophytes often host N<sub>2</sub>-fixing microorganisms (diazotrophs) that play a crucial role in the N cycle of these ecosystems. Despite their importance, how the bryophyte-associated N<sub>2</sub>-fixation varies across species and seasons (summer, autumn, winter, and spring) remains poorly understood. We measured N<sub>2</sub>-fixation rates for 10 bryophyte species in situ throughout the entire year in the Arctic with additional incubations to verify the method. We measured positive N<sub>2</sub>-fixation during most of the year, except for the coldest period (February). The species growing in the wettest conditions (<i>Sphagnum</i> spp.) had the highest N<sub>2</sub>-fixation rates in summer, while bryophytes in drier conditions peaked in N<sub>2</sub>-fixation rates in spring and autumn. The seasonal variation in N<sub>2</sub>-fixation activity was pronounced, but similar patterns were found among different species. This study reveals that bryophyte-associated N<sub>2</sub>-fixation in northern ecosystems is larger than previously assumed, as it occurs over a more extended part of the year than previously inferred. Furthermore, the importance of bryophyte-associated diazotrophs cannot be quantified without considering both the diversity of bryophytes and their variation in N<sub>2</sub>-fixing seasonal activity patterns. Both future changes in climatic conditions and biodiversity of bryophytes can thus have large implications for the N cycle in arctic regions.</p>

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Year-Round Variation in Bryophyte-Associated Nitrogen Fixation in the Arctic

  • 期刊论文

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  • 发表日期：

    2025年11月18日

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  • Emil Alexander Sherman Andersen,
  • Signe Lett,
  • Anders Michelsen,
  • Ellen Dorrepaal,
  • Johan Olofsson

摘要

In northern biomes, growth is nitrogen (N) limited, but bryophytes are abundant. These bryophytes often host N2-fixing microorganisms (diazotrophs) that play a crucial role in the N cycle of these ecosystems. Despite their importance, how the bryophyte-associated N2-fixation varies across species and seasons (summer, autumn, winter, and spring) remains poorly understood. We measured N2-fixation rates for 10 bryophyte species in situ throughout the entire year in the Arctic with additional incubations to verify the method. We measured positive N2-fixation during most of the year, except for the coldest period (February). The species growing in the wettest conditions (Sphagnum spp.) had the highest N2-fixation rates in summer, while bryophytes in drier conditions peaked in N2-fixation rates in spring and autumn. The seasonal variation in N2-fixation activity was pronounced, but similar patterns were found among different species. This study reveals that bryophyte-associated N2-fixation in northern ecosystems is larger than previously assumed, as it occurs over a more extended part of the year than previously inferred. Furthermore, the importance of bryophyte-associated diazotrophs cannot be quantified without considering both the diversity of bryophytes and their variation in N2-fixing seasonal activity patterns. Both future changes in climatic conditions and biodiversity of bryophytes can thus have large implications for the N cycle in arctic regions.