The seasonal growth pattern of Sphagnum magellanicum Brid. in different microhabitats on a mire in the southern Alps (Italy)

Abstract

On a nutrient-poor mire in the southern Alps of Italy Sphagnum magellanicum achieved a total linear elongation of 28-31 mm and a dry matter increment of 12-13 mg per plant during the growing season 1994. Sphagnum magellanicum grew actively whenever night temperature was above zero, but during this period growth was primarily controlled by water availability. The growth rates were very much the same in open sites compared to areas covered by Pinus mugo scrubs. However, plants growing in the two habitats showed different adaptations to environment. This implied a different pattern of physiological control on the growth rates of Sphagnum magellanicum in the two habitats. Provided the moisture content of the capitula was not limiting, the growth rates in shaded habitats were greatest when the concentrations of chlorophyll b as well as the ratio of chlorophyll to carotenoids were highest. Conversely, the growth rates in the open were negatively correlated with the ratio chlorophyll a to b, probably because chlorophyll a was degraded more rapidly than chlorophyll b in conditions of environmental stress. Red wall pigments (sphagnorubin s.l.) were more concentrated in the open, especially at the end of the growing season, the synthesis of such pigments being enhanced by high irradiance coupled with night chilling. However, the concentrations of sphagnorubin did not show the expected negative correlations with chlorophyll concentration and growth rate, presumably because of a different timing of the metabolic pathways of sphagnorubin synthesis and chlorophyll degradation.