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Functional Traits in Sphagnum
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Plant Ecology and Evolution.ORCID iD: 0000-0003-0497-8316
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Peat mosses (Sphagnum) are ecosystem engineers that largely govern carbon sequestration in northern hemisphere peatlands. I investigated functional traits in Sphagnum species and addressed the questions: (I) Are growth, photosynthesis and decomposition and the trade-offs between these traits related to habitat or phylogeny?, (II) Which are the determinants of decomposition and are there trade-offs between metabolites that affect decomposition?, (III) How do macro-climate and local environment determine growth in Sphagnum across the Holarctic?, (IV) How does N2 fixation vary among different species and habitats?, (V) How do species from different microtopographic niches avoid or tolerate desiccation, and are leaf and structural traits adaptations to growth high above the water table?

Photosynthetic rate and decomposition in laboratory conditions (innate growth and decay resistance) were related to growth and decomposition in their natural habitats. We found support for a trade-off between growth and decay resistance, but innate qualities translated differently to field responses in different species. There were no trade-offs between production of different decay-affecting metabolites. Their production is phylogenetically controlled, but their effects on decay are modified by nutrient availability in the habitat. Modelling growth of two species across the Holarctic realm showed that precipitation, temperature and vascular plant cover are the best predictors of performance, but responses were stronger for the wetter growing species. N2 fixation rates were positively related to moss decomposability, field decomposition and tissue phosphorus concentration. Hence, higher decomposition can lead to more nutrients available to N2-fixing microorganisms, while higher concentrations of decomposition-hampering metabolites may impede N2 fixation. A mesocosm experiment, testing effects of water level drawdown on water content and chlorophyll fluorescence, showed that either slow water loss or high maximum water holding capacity can lead to desiccation avoidance. Furthermore, leaf anatomical traits rather than structural traits affected the water economy.

This thesis has advanced the emerging field of trait ecology in Sphagnum by comparing many species and revealing novel mechanisms and an ever more complex picture of Sphagnum ecology. In addition, the species-specific trait measurements of this work offers opportunities for improvements of peatland ecosystem models.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 45
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1771
Keywords [en]
peat mosses, functional traits, NPP, decay resistance, N2 fixation, desiccation resistance, climate
National Category
Ecology
Research subject
Biology with specialization in Ecological Botany
Identifiers
URN: urn:nbn:se:uu:diva-375011ISBN: 978-91-513-0568-4 (print)OAI: oai:DiVA.org:uu-375011DiVA, id: diva2:1282760
Public defence
2019-03-15, Zootissalen, EBC, Villavägen 9, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2019-02-21 Created: 2019-01-25 Last updated: 2019-03-18
List of papers
1. Photosynthesis, growth, and decay traits in Sphagnum – a multispecies comparison
Open this publication in new window or tab >>Photosynthesis, growth, and decay traits in Sphagnum – a multispecies comparison
2016 (English)In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 6, no 10, p. 3325-3341Article in journal (Refereed) Published
Abstract [en]

Peat mosses (Sphagnum) largely govern carbon sequestration in Northern Hemisphere peatlands. We investigated functional traits related to growth and decomposition in Sphagnum species. We tested the importance of environment and phylogeny in driving species traits and investigated trade-offs among them. We selected 15 globally important Sphagnum species, representing four sections (subgenera) and a range of peatland habitats. We measured rates of photosynthesis and decomposition in standard laboratory conditions as measures of innate growth and decay potential, and related this to realized growth, production, and decomposition in their natural habitats. In general, we found support for a trade-off between measures of growth and decomposition. However, the relationships are not strong, with r ranging between 0.24 and 0.45 for different measures of growth versus decomposition. Using photosynthetic rate to predict decomposition in standard conditions yielded R2 = 0.20. Habitat and section (phylogeny) affected the traits and the trade-offs. In a wet year, species from sections Cuspidata and Sphagnum had the highest production, but in a dry year, differences among species, sections, and habitats evened out. Cuspidata species in general produced easily decomposable litter, but their decay in the field was hampered, probably due to near-surface anoxia in their wet habitats. In a principal components analysis, PCA, photosynthetic capacity, production, and laboratory decomposition acted in the same direction. The species were imperfectly clustered according to vegetation type and phylogeny, so that some species clustered with others in the same section, whereas others clustered more clearly with others from similar vegetation types. Our study includes a wider range of species and habitats than previous trait analyses in Sphagnum and shows that while the previously described growth–decay trade-off exists, it is far from perfect. We therefore suggest that our species-specific trait measures offer opportunities for improvements of peatland ecosystem models. Innate qualities measured in laboratory conditions translate differently to field responses. Most dramatically, fast-growing species could only realize their potential in a wet year. The same species decompose fast in laboratory, but their decomposition was more retarded in the field than that of other species. These relationships are crucial for understanding the long-term dynamics of peatland communities.

National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-284287 (URN)10.1002/ece3.2119 (DOI)000376646700024 ()27103989 (PubMedID)
Funder
Swedish Research CouncilSwedish Research Council FormasThe Royal Swedish Academy of Sciences
Available from: 2016-04-16 Created: 2016-04-16 Last updated: 2019-02-01Bibliographically approved
2. Biochemical determinants of litter quality in 15 species of Sphagnum
Open this publication in new window or tab >>Biochemical determinants of litter quality in 15 species of Sphagnum
2018 (English)In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 425, no 1-2, p. 161-176Article in journal (Refereed) Published
Abstract [en]

Background and aims Sphagnum mosses are ecosystem engineers that create and maintain boreal peatlands. With unique biochemistry, waterlogging and acidifying capacities, they build up meters-thick layers of peat, reducing competition and impeding decomposition. We quantify within-genus differences in biochemical composition to make inferences about decay rates, related to hummock-hollow and fen-bog gradients and to phylogeny. Methods We sampled litter from 15 Sphagnum species, abundant over the whole northern hemisphere. We used regression and Principal Components Analysis (PCA) to evaluate general relationships between litter quality parameters and decay rates measured under laboratory and field conditions. Results Both concentrations of the polysaccharide sphagnan and the soluble phenolics were positively correlated with intrinsic decay resistance, however, so were the previously understudied lignin-like phenolics. More resistant litter had more of all the important metabolites; consequently, PC1 scores were related to lab mass loss (R-2 = 0.57). There was no such relationship with field mass loss, which is also affected by the environment. PCA also revealed that metabolites clearly group Sphagnum sections (subgenera). Conclusions We suggest that the commonly stated growth-decomposition trade-off is largely due to litter quality. We show a strong phylogenetic control on Sphagnum metabolites, but their effects on decay are affected by nutrient availability in the habitat.

Keywords
Peatland, Decay resistance, Sphagnan, Phenolics, Lignin, Hummock-hollow
National Category
Botany
Identifiers
urn:nbn:se:uu:diva-354249 (URN)10.1007/s11104-018-3579-8 (DOI)000430992300011 ()
Funder
Swedish Research CouncilThe Royal Swedish Academy of Sciences
Note

Correction in: PLANT AND SOIL, Volume: 439, Issue: 1-2, Pages: 569-572, Special Issue: SI, DOI: 10.1007/s11104-019-04046-5

Available from: 2018-06-29 Created: 2018-06-29 Last updated: 2019-08-16Bibliographically approved
3. Environmental drivers of Sphagnum growth in mires across the Holarctic region
Open this publication in new window or tab >>Environmental drivers of Sphagnum growth in mires across the Holarctic region
(English)Manuscript (preprint) (Other academic)
Keywords
climate, global change, NPP, peatlands, peat mosses, nitrogen deposition
National Category
Natural Sciences
Research subject
Biology with specialization in Ecological Botany; Biology with specialization in Ecological Botany
Identifiers
urn:nbn:se:uu:diva-375010 (URN)
Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-02-01
4. Variation in symbiotic Nfixation among Sphagnum and feather mosses
Open this publication in new window or tab >>Variation in symbiotic Nfixation among Sphagnum and feather mosses
Show others...
(English)Manuscript (preprint) (Other academic)
Keywords
diazotrophs, peat moss, bog, peatland, nitrogen, phosphorus, carbon, nutrient cycling, traits, boreal forest
National Category
Natural Sciences
Research subject
Biology with specialization in Ecological Botany
Identifiers
urn:nbn:se:uu:diva-375008 (URN)
Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-02-01
5. Mechanisms behind species-specific water economy responses to water level drawdown in peat mosses
Open this publication in new window or tab >>Mechanisms behind species-specific water economy responses to water level drawdown in peat mosses
(English)Manuscript (preprint) (Other academic)
Keywords
peat mosses, water economy, capitulum water content, bulk density, hyaline cell, pore size, leaf anatomy
National Category
Natural Sciences
Research subject
Biology with specialization in Ecological Botany
Identifiers
urn:nbn:se:uu:diva-375009 (URN)
Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-02-01

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