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Ecophysiological adjustment of two Sphagnum species in response to anthropogenic nitrogen deposition
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2009 (English)In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 181, no 1, 208-217 p.Article in journal (Refereed) Published
Abstract [en]

We asked whether Sphagnum species have adjusted their N uptake in response to the anthropogenic N deposition that has drastically altered N-limited ecosystems, including peatlands, worldwide. A lawn species, S. balticum, and a hummock species, S. fuscum, were collected from three peatlands along a gradient of N deposition (2, 8 and 12 kg N ha-1 yr-1). The mosses were subjected to solutions containing a mixture of four N forms. In each solution one of these N forms was labeled with 15N (viz. 15NH4+, 15NO3- and the amino acids [15N]alanine (ALA) and [15N]glutamic acid (GLU)). We found for both species that the majority of the N taken up was from NH4+, followed by ALA, GLU, and very small amounts of NO3-. At the highest N deposition site N uptake was reduced, but this did not prevent N accumulation as free amino acids in the Sphagnum tissues. The reduced N uptake may have been genetically selected for under the relatively short period with elevated N exposure from anthropogenic sources, or may have been the result of plasticity in the Sphagnum physiological response. The negligible Sphagnum NO3- uptake may make any NO3- deposited readily available to co-occurring vascular plants.

Place, publisher, year, edition, pages
2009. Vol. 181, no 1, 208-217 p.
URN: urn:nbn:se:umu:diva-23284DOI: 10.1111/j.1469-8137.2008.02628.xOAI: diva2:222608
Available from: 2009-06-09 Created: 2009-06-09 Last updated: 2016-02-08Bibliographically approved
In thesis
1. Responses of peatland vegetation to enhanced nitrogen
Open this publication in new window or tab >>Responses of peatland vegetation to enhanced nitrogen
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Human alteration of the global nitrogen (N) cycle has had major impacts on naturally N-limited ecosystems worldwide. Peatlands, dominated by peat mosses, Sphagnum species, represent one such sensitive ecosystem. I have studied how this ecosystem is affected by increased N availability, using a small-scale N fertilization experiment in combination with a gradient study of three peatlands with varying N deposition.

I found both in the experiment and in the gradient a similar pattern of Sphagnum decline accompanied by an increase of vascular plants associated with enhanced N supply. For one common Sphagnum species - both in the experiment and in the gradient study - I also found an identical, linear increase in soluble amino acid N (NAA) accumulation. As soluble amino acids function as N storage compounds among Sphagna, NAA is a suitable measure for Sphagnum N status, and indicates accumulation of excess N not used for growth. My results show that NAA can be used as a sensitive indicator to signal N pollution before the slow, and gradual, regime shift from Sphagnum to vascular plant dominance is visible. In an N-uptake experiment using Sphagnum specimens from the three peatlands varying in N deposition, I found a reduced N-uptake by both investigated Sphagnum species from a high N deposition site, in south-western Sweden. This potential of Sphagna to adjust to high N loads through N uptake regulation will, however, not prevent tissue N accumulation, and as a result a shift from Sphagnum to vascular plant dominance.

In general I found similar patterns of N induced changes both in Sphagnum tissue chemistry and vegetation structure in the experiment and along the gradient study. Thus, I conclude that long-term, small-scale field experiments seem to offer reliable estimates of both the direction and strength of key vegetation responses in Sphagnum dominated peatlands. This is likely related to the key role of Sphagna as ecosystem engineers.

In the experiment I found a marked time lag in vegetation response to N application treatments. The closed Sphagnum carpet did not collapse until after eight years of continuous treatments. Another result was that dwarf shrubs, e.g. cranberry Vaccinium oxycoccos, first increased, but later declined due to severe attacks by fungal diseases. One important conclusion is that long-term, manipulative field experiments are necessary for our ability to understand how ecosystems will respond to environmental change.

Place, publisher, year, edition, pages
Umeå: Ekologi, miljö och geovetenskap, 2008. 24 p.
Sphagnum, nitrogen, peatlands, soluble amino acids, gradient study, field experiment
National Category
Biological Sciences
urn:nbn:se:umu:diva-1655 (URN)978-91-7264-551-6 (ISBN)
Public defence
2008-06-05, Lilla Hörsalen, KBC, SE-90187, Umeå, 10:00 (English)
Available from: 2008-05-15 Created: 2008-05-15 Last updated: 2016-02-08Bibliographically approved

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Wiedermann, Magdalena MEricson, Lars
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