Moss Responses to Elevated CO2 and Variation in Hydrology in a Temperate Lowland Peatland

Abstract

We studied the effects of elevated CO 2 (180 -200 ppmv above ambient) on growth and chemistry of three moss species (Sphagnum palustre, S. recurvum and Polytrichum commune) in a lowland peatland in the Netherlands. Thereto, we conducted both a greenhouse experiment with both Sphagnum species and a field experiment with all three species using MiniFACE (Free Air CO 2 Enrichment) technology during 3 years. The greenhouse experiment showed that Sphagnum growth was stimulated by elevated CO 2 in the short term, but that in the longer term ( ‡1 year) growth was probably inhibited by low water tables and/or downregulation of photosynthesis. In the field experiment, we did not find significant changes in moss abundance in response to elevated CO 2 , although CO 2 enrichment appeared to reduce S. recurvum abundance. Both Sphagnum species showed stronger responses to spatial variation in hydrology than to increased atmospheric CO 2 concentrations. Polytrichum was insensitive to changes in hydrology. Apart from the confounding effects of hydrology, the relative lack of growth response of the moss species may also have been due to the relatively small increase in assimilated CO 2 as achieved by the experimentally added CO 2 . We calculated that the added CO 2 contributed at most 32% to the carbon assimilation of the mosses, while our estimates based on stable C isotope data even suggest lower contributions for Sphagnum (24 -27%). Chemical analyses of the mosses showed only small elevated CO 2 effects on living tissue N concentration and C/N ratio of the mosses, but the C/N ratio of Polytrichum was substantially lower than those of the Sphagnum species. Continuing expansion of Polytrichum at the expense of Sphagnum could reduce the C sink function of this lowland Sphagnum peatland, and similar ones elsewhere, as litter decomposition rates would probably be enhanced. Such a reduction in sink function would be driven mostly by increased atmospheric N deposition, water table regulation for agricultural purposes and land management to preserve the early successional stage (mowing, tree and shrub removal), since these anthropogenic factors will probably exert a greater control on competition between Polytrichum and Sphagnum than increased atmospheric CO 2 concentrations.

Mineral nitrogen and phosphorus pools affected by water table lowering and warming in a boreal forested peatland

“…Shading has been found to significantly reduce the C:N ratio of Sphagnum capitula from ~54 to ~27 from peat mesocosms removed from a raised bog in Upper Teesdale, UK (Bonnett, Ostle, & Freeman, ). Although C:N over 100 has been reported for Sphagnum litter (Asada, Warner, & Aravena, ), several studies report values similar to this study of 30–50 (e.g., Limpens, Berendse, & Klees, ; Péli, Nagy, & Cserhalmi, ; Toet et al, ). We also observed that C:N ratio of Sphagnum was similar to the leaves of R. groenlandicum , a result consistent with reported C:N ratios from a range of plant functional types in a shrubby ombrotrophic bog in eastern Canada (Wang & Moore, ).…”

Rapid loss of an ecosystem engineer: Sphagnum decline in an experimentally warmed bog

“…Mini‐FACE experiments in four predominantly ombrotrophic peat bogs in Finland, Sweden, the Netherlands, and Switzerland showed no effect of elevated CO 2 on Sphagnum biomass over 3 years (Hoosbeek et al, ). In a greenhouse experiment, Sphagnum growth was initially stimulated by elevated CO 2 , but the response did not persist in the second year of exposure, and in the field, Sphagnum responded more to spatial variation in hydrology than to atmospheric CO 2 concentrations (Toet et al, ). In contrast with vascular plants for which effects of elevated CO 2 on photosynthesis and stomatal conductance are well documented (Ainsworth & Long, ), Sphagnum photosynthesis is controlled more by water content (Schipperges & Rydin, ; Williams & Flanagan, ), and stomatal responses are precluded.…”

The role of northern peatlands in the global carbon cycle for the 21st century

“…Field studies and laboratory experiments show that the CO 2 fertilization effect on plant growth should be smaller in peatlands than in other northern ecosystems. On the one hand, some moss species were found not to be stimulated by elevated CO 2 (Berendse et al, 2001; Toet, 2006). On the other hand, the effects of CO 2 on growth of vascular plants in peatland might be limited by low nitrogen availability in oligotrophic peatlands (Hoosbeek et al, 2001).…”