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

Masaaki Chiwa, Lucy J. Sheppard, Ian D. Leith, Sarah R. Leeson, Y. Sim Tang, J. Neil Cape

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)113-120
Number of pages8
JournalScience of the Total Environment
Volume559
DOIs
Publication statusPublished - Jul 15 2016

Fingerprint

porewater
filter
Water
bog
critical load
wet deposition
Ammonium Compounds
peatland
Nitrates
moss
Ecosystems
Leaching
Nutrients
Water quality
Anions
effect
Cations
Protons
anion
ion exchange

All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

Cite this

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.

In: Science of the Total Environment, Vol. 559, 15.07.2016, p. 113-120.

Research output: Contribution to journalArticle

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