Sphagnum growth and ecophysiology during mire succession

Abstract

Sphagnum mosses are widespread in areas where mires exist and constitute a globally important carbon sink. Their ecophysiology is known to be related to the water level, but very little is currently known about the successional trend in Sphagnum. We hypothesized that moss species follow the known vascular plant growth strategy along the successional gradient (i.e., decrease in production and maximal photosynthesis while succession proceeds). To address this hypothesis, we studied links between the growth and related ecophysiological processes of Sphagnum mosses from a time-since-initiation chronosequence of five wetlands. We quantified the rates of increase in biomass and length of different Sphagnum species in relation to their CO(2) assimilation rates, their photosynthetic light reaction efficiencies, and their physiological states, as measured by the chlorophyll fluorescence method. In agreement with our hypothesis, increase in biomass and CO(2) exchange rate of Sphagnum mosses decreased along the successional gradient, following the tactics of more intensely studied vascular plants. Mosses at the young and old ends of the chronosequence showed indications of downregulation, measured as a low ratio between variable and maximum fluorescence (F(v)/F(m)). Our study divided the species into three groups; pioneer species, hollow species, and ombrotrophic hummock formers. The pioneer species S. fimbriatum is a ruderal plant that occurred at the first sites along the chronosequence, which were characterized by low stress but high disturbance. Hollow species are competitive plants that occurred at sites with low stress and low disturbance (i.e., in the wet depressions in the middle and at the old end of the chronosequence). Ombrotrophic hummock species are stress-tolerant plants that occurred at sites with high stress and low disturbance (i.e., at the old end of the chronosequence). The three groups along the mire successional gradient appeared to be somewhat analogous to the three primary strategies suggested by Grime.

Methanotrophy induces nitrogen fixation during peatland development

“…This proportion is in agreement with the recent estimate of 35% for Sphagnum riparium, inferred from N content and growth rate in a 2-mo laboratory experiment (6). Despite the low absolute areal rate of N 2 fixation in the older mainly rainwater-fed stages (fen-bog transitions), where moss growth is more nutrient limited, the comparison of Sphagnum growth rates (26) and N contents further suggests that the proportion of fixed N of the new biomass N increment may increase to 58%. The rest of the N is, we presume, being taken up as inorganic ions and organic N, or recycled to new growth from older parts of the moss shoot (29).…”

“…At these sites, 30-65% of annual moss growth occurs during the October-April period, outside the traditionally defined growing season (26).…”

Restoration of ecosystem structure and function in boreal spruce swamp forests

“…7). Sphagnum biomass increment in the spruce swamp forests was similar to the increment in ombrotrophic bogs (Laine et al 2011); a similar conclusion has been drawn previously by Pakarinen and Rinne (1979). However, because Sphagnum species of nutrient-rich habitats decompose more rapidly than Sphagna of nutrient-poor habitats (Johnson and Damman 1991, Beleya 1996, Limpens and Berendse 2003 carbon accumulation in Sphagnum biomass is likely to be less than in poorer systems.…”

Behind the stability of boreal bog carbon sink: Compositional and functional variation of vegetation across temporal and spatial scales

“…Lawn Sphagnum structural tissues are stimulated by CO2 originating from the decomposition below, which allows them to rise above hollow species and outcompete them (Smolders et al 2001). Hollow Sphagna are more productive in terms of biomass increment and photosynthesis rate (Gunnarsson 2005;Granath et al 2009;Laine et al 2011), but their lower drought resistance limits their habitat to the wet surfaces (van Breemen 1995;Väliranta et al 2007). These habitats created by Sphagnum mosses favor different composition of vascular plant species.…”

“…In this context, water table gradient is an abstract concept referring to a gradual change in plant species composition in relation to moisture instead of an actual, physical gradient. Plant species typical for the dry end of the water table gradient, hummock Sphagna and dwarf-shrubs, are known to have lower photosynthesis rate than sedges or lawn and hollow Sphagna (Leppälä et al 2008;Laine et al 2011). Despite this, hummocks are known to often have higher photosynthesis than the wetter plant communities due to their generally higher photosynthesizing leaf area Munir et al 2014).…”