Proceedings of the 14th International Peat Congress
Haraguchi 2012: Photosynthetic responses in Sphagnum spp. in temperate mires to temperature, pH and salinity
Theme I. Inventory, stratigraphy and conservation of mires and peatlands
Sphagnum spp. are dominant peat forming plants mainly distributed in low temperature, high acidity and low salinity environments. We investigated photosynthetic responses of Sphagnum spp. to temperature, pH and salinity to test if Sphagnum spp. are physiologically adapted to these environments. We investigated the temperature dependency (range 5-40 °C) of gross photosynthetic rates for Sphagnum palustre, S. fimbriatum, S. papillosum, S. fuscum and S. fallax. The maximum photosynthetic rate was obtained at 30-35 °C for all species. Photosynthetic rates of all these species
showed a maximum at 300-500 micromol m-2 s-1 of PPFD and it decreased at higher PPFD (> 500 micro-mol m-2 s-1) under low temperature (5-10 °C). The pH dependence (range 3.8-10.0) of gross photosynthetic rate was investigated for S. palustre, S. cuspidatum, S. squarrosum, S. girgensohnii, S. fuscum, S. rubellum and S. magellanicum. Most of the species showed optimal pH at 5.0-6.0, although the rate at pH=9.0 was 50-80 % of the rate at the optimal pH for photosynthesis. The salinity dependence (range 0-40 mM NaCl) of gross photosynthetic rate was investigated for S. palustre and S. fimbriatum. The rate of plants cultivated in 1-40 mM NaCl solution (pH=6.0) for 2 days showed ca.
2/3 of that in plants cultivated in pure water. These results on temperature, pH and salinity dependency of photosynthetic rate imply that Sphagnum spp. are not specifically adapted to the mire environments where they dominate.