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Physiological responses to nitrogen and sulphur addition and raised temperature in Sphagnum balticum
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Ecological Botany.
2009 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 161, no 3, 481-490 p.Article in journal (Refereed) Published
Abstract [en]

Sphagnum, the main genus which forms boreal peat, is strongly affected by N and S deposition and raised temperature, but the physiological mechanisms behind the responses are largely unknown. We measured maximum photosynthetic rate (NPmax), maximum efficiency of photosystem II [variable fluorescence (F v)/maximum fluorescence yield (F m)] and concentrations of N, C, chlorophyll and carotenoids as responses to N and S addition and increased temperature in Sphagnum balticum (a widespread species in the northern peatlands) in a 12-year factorial experiment. NPmax did not differ between control (0.2 g N m−2 year−1) and high N (3.0 g N m−2 year−1), but was higher in the mid N treatment (1.5 g N m−2 year−1). N, C, carotenoids and chlorophyll concentration increased in shoot apices after N addition. F v/F m did not differ between N treatments. Increased temperature (+3.6°C) had a small negative effect on N concentration, but had no significant effect on NPmax or F v/F m. Addition of 2 g S m−2 year−1 showed a weak negative effect on NPmax and F v/F m. Our results suggest a unimodal response of NPmax to N addition and tissue N concentration in S. balticum, with an optimum N concentration for photosynthetic rate of ~13 mg N g−1. In conclusion, high S deposition may reduce photosynthetic capacity in Sphagnum, but the negative effects may be relaxed under high N availability. We suggest that previously reported negative effects on Sphagnum productivity under high N deposition are not related to negative effects on the photosynthetic apparatus, but differences in optimum N concentration among Sphagnum species may affect their competitive ability under different N deposition regimes.

Place, publisher, year, edition, pages
2009. Vol. 161, no 3, 481-490 p.
Keyword [en]
Chlorophyll fluorescence, Nutrient deposition, Peatlands, Photosynthesis, Photosynthetic nitrogen use efficiency
National Category
Biological Sciences
URN: urn:nbn:se:uu:diva-120447DOI: 10.1007/s00442-009-1406-xISI: 000269010300004PubMedID: 19593588OAI: oai:DiVA.org:uu-120447DiVA: diva2:303357
Available from: 2010-03-12 Created: 2010-03-12 Last updated: 2012-02-15Bibliographically approved
In thesis
1. Peatland Bryophytes in a Changing Environment: Ecophysiological Traits and Ecosystem Function
Open this publication in new window or tab >>Peatland Bryophytes in a Changing Environment: Ecophysiological Traits and Ecosystem Function
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Peatlands are peat forming ecosystems in which not fully decomposed plant material builds up the soil. The sequestration of carbon into peat is mainly associated with the bryophyte genus Sphagnum (peat mosses), which dominate and literally form most peatlands. The responses of Sphagnum to environmental change help us to understand peatland development and function and to predict future changes in a rapidly changing world. In this thesis, the overarching aim was to use ecophysiological traits to investigate mechanisms behind the response of Sphagnum to elevated N deposition, and, processes connected to ecosystem shift and ecosystem function of peatlands.

Regarding elevated N deposition, three experiments were performed at different scales (country-wide to greenhouse). Independent of scale and species, apical tissue N concentration increased with increasing N input until N saturation was reached. Maximum photosynthetic rate, a trait evaluating photosynthetic capacity, increased with N input and could be well predicted by tissue N concentration. Thus, the physiological responses of Sphagnum to N deposition are often positive and I found no evidence of toxic effects. Production did, however, not increase with N input, and results of the N:P ratio suggested that P limitation, and possibly other elements, might hamper growth under high N input. The effect of P limitation was, in contrast to current view, most pronounced in fast growing species indicating species specific responses to nutrient imbalance.

I explored the puzzling, but historically frequently occurring, rich fen to bog ecosystem shift; a shift from a species-rich ecosystem dominated by brown mosses, to a species-poor one with greater carbon storage that is Sphagnum-dominated. The bog-dwelling species of Sphagnum grew well, to our surprise, when in contact with rich fen water but was not a strong competitor compared to rich fen Sphagnum species. If submerged under rich fen water (high pH), the bog Sphagnum species died while rich fen species of Sphagnum were unaffected. These results show that differences in two physiological traits (growth rate and tolerance to flooding) among species, can explain when a peatland ecosystem shift might occur.

In the last study, the function of peatlands was related to trade-offs between traits and allometric scaling in Sphagnum. Results suggested that growth strategies are determined by the distribution of Sphagnum relative to the water table in order to minimize periods with suboptimal hydration. Allometric analyses stressed the importance of resource allocation among and within shoots (apical part vs. stem), although the allocation patterns in Sphagnum were not always consistent with those of vascular plants. Interestingly, data indicated a trade-off between photosynthetic rate and decomposition rate among Sphagnum species.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 39 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 889
allometric scaling, chlorophyll fluorescence, competition, decomposition, flooding, mire, N concentration, nitrogen deposition, photosynthesis, succession, stoichiometry
National Category
Research subject
Ecological Botany
urn:nbn:se:uu:diva-165138 (URN)978-91-554-8249-7 (ISBN)
Public defence
2012-02-17, Zootissalen, EBC, Villavägen 9, Uppsala, 10:00 (English)
Available from: 2012-01-27 Created: 2012-01-03 Last updated: 2012-02-15Bibliographically approved

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