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 specie s (S. capillifolium, S. magellanicum and S. fallax) were measured duri ng three consecutive growing seasons at a nutrient-poor mire in the so uthern 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 Individu als of all three species were also cultured in the laboratory under di fferent combinations of photoperiod x photon flux density x night temp erature. The resulting growth data were compared by two-way ANOVA. 3 L ong-day photoperiod promoted growth of all species. Induction of dorma ncy required both short-day photoperiod and low night temperature. 4 M ean temperature had a positive effect on growth of both S. capillifoli um and S. magellanicum. Growth of S. fallax, a species which is more p rone to desiccation in dry periods, was more affected by water-table d epth. 5 The periodic pattern of dry-matter accumulation in Sphagnum is controlled partly by an as yet unknown internal rhythm based on photo period, and partly by external factors related to climate. However, th e response of Sphagnum to environment differs between species and is r eflected in the competitive equilibria between species that are adapte d to different microhabitats. Hollow species are usually more producti ve than hummock species in wet periods but this ratio often reverses i n dry periods.