Effect of Water Level on Desiccation of Sphagnum in Relation to Surrounding Sphagna

Abstract

Desiccation of Sphagnum during periods of dry weather and low water table in a mire was followed by measuring the capitulum water content. The lower the water content, the greater the desiccation. For four investigated species desiccation increased in the order S. fuscum < S. rubellum < S. balticum < S. tenellum. The same ranking was found in a laboratory experiment in which the species were exposed to a gradually lowered water table. This ranking is related to the uppermost levels reached by the species on the hummocks of the mire. It is argued that the frequency and degree of desiccation, being more severe in the hollow species, will prevent these from growing on the hummocks. The specific identity of the Sphagnum surrounding the investigated capitulum has a profound effect on the course of its desiccation. Capitula of a species that normally dries out quickly (S. balticum, S. tenellum) benefit from being surrounded by shoots of superior species (S. fuscum, S. rubellum). This may explain the observation that individual shoots of S. balticum can be found at a higher level above the water table in a S. fuscum-hummock than in single-species carpets of S. balticum. This may be interpreted as a case of commensalism, acting in combination with competition.