Data from: Photosynthesis, growth, and decay traits in Sphagnum – a multispecies comparison

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.