Sphagnum can ‘filter’ N deposition, but effects on the plant and pore water depend on the N form

Chiwa, Masaaki; Sheppard, Lucy J.; Leith, Ian D.; Leeson, Sarah R.; Tang, Y. Sim; Cape, J. Neil. 2016 Sphagnum can ‘filter’ N deposition, but effects on the plant and pore water depend on the N form. Science of the Total Environment, 559. 113-120. 10.1016/j.scitotenv.2016.03.130

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Abstract/Summary

The ability of Sphagnum moss to efficiently intercept atmospheric nitrogen (N) has been assumed to be vulnerable to increased N deposition. However, the proposed critical load (20 kg N ha− 1 yr− 1) to exceed the capacity of the Sphagnum N filter has not been confirmed. A long-term (11 years) and realistic N manipulation on Whim bog was used to study the N filter function of Sphagnum (Sphagnum capillifolium) in response to increased wet N deposition. On this ombrotrophic peatland where ambient deposition was 8 kg N ha− 1 yr− 1, an additional 8, 24, and 56 kg N ha− 1 yr− 1 of either ammonium (NH4+) or nitrate (NO3−) has been applied for 11 years. Nutrient status of Sphagnum and pore water quality from the Sphagnum layer were assessed. The N filter function of Sphagnum was still active up to 32 kg N ha− 1 yr− 1 even after 11 years. N saturation of Sphagnum and subsequent increases in dissolved inorganic N (DIN) concentration in pore water occurred only for 56 kg N ha− 1 yr− 1 of NH4+ addition. These results indicate that the Sphagnum N filter is more resilient to wet N deposition than previously inferred. However, functionality will be more compromised when NH4+ dominates wet deposition for high inputs (56 kg N ha− 1 yr− 1). The N filter function in response to NO3− uptake increased the concentration of dissolved organic N (DON) and associated organic anions in pore water. NH4+ uptake increased the concentration of base cations and hydrogen ions in pore water though ion exchange. The resilience of the Sphagnum N filter can explain the reported small magnitude of species change in the Whim bog ecosystem exposed to wet N deposition. However, changes in the leaching substances, arising from the assimilation of NO3− and NH4+, may lead to species change.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1016/j.scitotenv.2016.03.130
UKCEH and CEH Sections/Science Areas:	UKCEH Fellows Dise
ISSN:	0048-9697
Additional Keywords:	manipulation experiment, tissue N, dissolved organic nitrogen, base cations, N uptake
NORA Subject Terms:	Ecology and Environment
Date made live:	12 Aug 2016 13:39 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/514258

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