Biomass, productivity and relative rate of photosynthesis of Sphagnum at different water levels on a South Swedish peat bog

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Abstract
The distribution pattern of Sphagnum species on bogs follows a hummock‐hollow gradient. S. Sect. Acutifolia (that is in this study S. fuscum and S. rubellum combined) dominates hummock tops, ca 20 cm above the maximum water level with a green biomass of 50 g m−2, S. magellancium dominates at a lower level, about 5 cm above the water level with a green biomass of 75 g m−2 and S. cuspidatum dominates in the wettest hollows with a green biomass of about 50 g m−2.In situ measurements of length growth of S. Sect. Acutifolia and S. magellanicum using a 14CO2‐labelling technique during three consecutive years, revealed an unexpectedly high between‐year variation in length growth of 7‐23 mm yr−1, and 16‐22 mm yr−1, respectively. Consequently the dominating producer in the transition between hummock and hollow changes from year to year, probably depending on climatic conditions.In vitro experiments on the effects of different water levels of 2, 5, 10 and 20 cm below the moss surface, on photosynthetic activity of S. Sect. Acutifolia and S. magellanicum, measured by a second 14CO2‐technique, indicate optimal conditions for S. magellanicum at 10 cm above water level, and for S. Sect, Acutifolia at 20 cm above water level.Differences in capillary water transport capability between the species are more important than the sensitivity of photosynthesis to water stress in explaining field patterns of productivity and distribution.