The Growth Dynamics of Sphagnum Based on Field Measurements in a Temperate Bog and on Laboratory Cultures

1 Linear elongation and dry-matter production of three Sphagnum species (S. capillifolium, S. magellanicum and S. fallax) were measured during three consecutive growing seasons at a nutrient-poor mire in the southern Alps of Italy. The growth data were subjected to path analysis, in which climatic parameters, distance to water table and photoperiod were employed as independent variables in the regressions. 2 Individuals of all three species were also cultured in the laboratory under different combinations of photoperiod x photon flux density x night temperature. The resulting growth data were compared by two-way ANOVA. 3 Long-day photoperiod promoted growth of all species. Induction of dormancy required both short-day photoperiod and low night temperature. 4 Mean temperature had a positive effect on growth of both S. capillifolium and S. magellanicum. Growth of S. fallax, a species which is more prone to desiccation in dry periods, was more affected by water-table depth. 5 The periodic pattern of dry-matter accumulation in Sphagnum is controlled partly by an as yet unknown internal rhythm based on photoperiod, and partly by external factors related to climate. However, the response of Sphagnum to environment differs between species and is reflected in the competitive equilibria between species that are adapted to different microhabitats. Hollow species are usually more productive than hummock species in wet periods but this ratio often reverses in dry periods.