Variation in symbiotic N2 fixation rates among Sphagnum mosses

PLoS One. 2020 Feb 4;15(2):e0228383. doi: 10.1371/journal.pone.0228383. eCollection 2020.

Abstract

Biological nitrogen (N) fixation is an important process supporting primary production in ecosystems, especially in those where N availability is limiting growth, such as peatlands and boreal forests. In many peatlands, peat mosses (genus Sphagnum) are the prime ecosystem engineers, and like feather mosses in boreal forests, they are associated with a diverse community of diazotrophs (N2-fixing microorganisms) that live in and on their tissue. The large variation in N2 fixation rates reported in literature remains, however, to be explained. To assess the potential roles of habitat (including nutrient concentration) and species traits (in particular litter decomposability and photosynthetic capacity) on the variability in N2 fixation rates, we compared rates associated with various Sphagnum moss species in a bog, the surrounding forest and a fen in Sweden. We found appreciable variation in N2 fixation rates among moss species and habitats, and showed that both species and habitat conditions strongly influenced N2 fixation. We here show that higher decomposition rates, as explained by lower levels of decomposition-inhibiting compounds, and higher phosphorous (P) levels, are related with higher diazotrophic activity. Combining our findings with those of other studies, we propose a conceptual model in which both species-specific traits of mosses (as related to the trade-off between rapid photosynthesis and resistance to decomposition) and P availability, explain N2 fixation rates. This is expected to result in a tight coupling between P and N cycling in peatlands.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ecosystem
  • Forests
  • Models, Theoretical
  • Nitrogen / analysis*
  • Nitrogen Fixation
  • Phosphorus / analysis*
  • Photosynthesis
  • Sphagnopsida / classification
  • Sphagnopsida / growth & development*
  • Sphagnopsida / metabolism
  • Sweden
  • Symbiosis

Substances

  • Phosphorus
  • Nitrogen

Grant support

The Swedish Research Council (contract 2015-05174 to HR). The Dutch National Research Organization (‘Cinderella’ ERA-Net project, NWO-grant 861.15.001 to CF). No - The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.