Abstract
Background and aimsSphagnum 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.MethodsWe 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.ResultsBoth 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 (R2 = 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).ConclusionsWe 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.
Highlights
Northern peatlands store immense amounts of carbon, according to a recent estimate 436 Gt (Loisel et al 2014), which is equivalent to >50% of the carbon stored as CO2 in the atmosphere (IPCC 2013)
Hájek Department of Functional Ecology, Institute of Botany of the Czech Academy of Sciences, Dukelská 135, CZ-379 82 Třeboň, Czech Republic parameters and decay rates measured under laboratory and field conditions. Both concentrations of the polysaccharide sphagnan and the soluble phenolics were positively correlated with intrinsic decay resistance, so were the previously understudied lignin-like phenolics
The sections of the genus Sphagnum differed in concentrations of sphagnan, phenolics and Klason lignin, and in cation exchange capacity (CEC) (ANOVA: P < 0.0001 for all; Fig. 1, detailed data in Supplementary Tables 1 and 2), with the differences generally due to high concentrations in sect
Summary
Northern peatlands store immense amounts of carbon, according to a recent estimate 436 Gt (Loisel et al 2014), which is equivalent to >50% of the carbon stored as CO2 in the atmosphere (IPCC 2013). The carbon is stored as peat, i.e. poorly decomposed organic matter. This is largely due to anoxia in the waterlogged habitat and the litter quality of the species that occupy these peatlands. Make up around 45% of the peat in boreal peatlands (Turetsky 2003) and are the organisms creating and maintaining many of these ecosystems, bogs (Rydin and Jeglum 2013). Anoxia is linked to the lower peat layers (the permanently water-logged catotelm), while the acrotelm is intermittently oxic (Morris et al 2011; Rydin and Jeglum 2013). Knowledge about the litter quality of ecosystem engineers, such as Sphagnum spp., is crucial to the understanding of ecosystem functions in northern peatlands. Sphagnum mosses are ecosystem engineers that create and maintain boreal peatlands. 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
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