Biological nitrogen fixation (BNF) represents the natural pathway by which mosses meet their demands for bioavailable/reactive nitrogen (Nr) in peatlands. However, following intensification of nitrogen fertilizer and fossil fuel use, atmospheric Nr deposition has increased exposing peatlands to Nr loading often above the ecological threshold. As BNF is energy intensive, therefore, it is unclear whether BNF shuts down when Nr availability is no longer a rarity. We studied the response of BNF under a gradient of Nr deposition extending over decades in three peatlands in the U.K., and at a background deposition peatland in Sweden. Experimental nitrogen fertilization plots in the Swedish site were also evaluated for BNF activity. In situ BNF activity of peatlands receiving Nr deposition of 6, 17, and 27 kg N ha-1 yr-1 was not shut down but rather suppressed by 54, 69, and 74%, respectively, compared to the rates under background Nr deposition of μ2 kg N ha-1 yr-1. These findings were corroborated by similar BNF suppression at the fertilization plots in Sweden. Therefore, contribution of BNF in peatlands exposed to chronic Nr deposition needs accounting when modeling peatland's nitrogen pools, given that nitrogen availability exerts a key control on the carbon capture of peatlands, globally.
Bibliographical noteFunding Information:
We acknowledge the financial support of the Keele University ACORN Program, UK CEH Life Sciences Mass Spectrometry Facility at Lancaster, UKRI NERC macronutrient cycle program grant (NE/J011541/1) and the British Bryological Society for this project. We thank Dr. A. Stott at UK CEH, the National Trust and Natural England for allowing us access to their sites for research in the U.K. The Swedish Infrastructure for Ecosystem Science (SITES) is acknowledged for the support through the Svartberget Experimental Forests facilities. The help of Dr J. Daniels at the Natural England's Fenns-Whixal peatland site in identifying moss species is also aknowledged.The technical staff at the Svartberget Experimental Forests is also specifically acknowledged.
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- Nassimilation method
- biological nitrogen fixation
- nitrogen biogeochemistry
- Nr deposition
- Sphagnum mosses