Growth depends on neighbours: experiments with three Sphagnum L. species

Abstract

Our aim was to search for reasons why some peat mosses (Sphagnum), despite having wide distribution areas, consistently occur in small and distantly scattered populations. The effect of interspecific interactions was proposed as the main hypothesis. Three Sphagnum species exhibiting different distribution frequencies (S. wulfianum Girg., S. teres (Schimp.) Ångstr., and S. magellanicum Brid.) were selected, and two experiments in controlled conditions were established. In the first experiment, the peat mosses were grown in mono-species, two-species, and three-species mixtures. Only the growth of the species with the most restricted distribution (S. wulfianum) responded significantly to the presence of the other Sphagnum species. In the second experiment, shoots of S. wulfianum were watered with the exudates and extracts of the other two species. Significant effects were observed on the growth of S. wulfianum. We conclude that neighbour species can suppress the growth of some bryophyte species and possibly limit their natural distribution.