| Summary: | Degraded rangelands are common in Iceland, with harsh environmental conditions, volcanism and overgrazing being the primary contributors. Overgrazing, in turn, causes a dominance shift in favour of unpalatable plants, which, once established, maintain their dominance through mechanisms including allelopathy. Allelopathic plants produce allelochemicals, which are secondary metabolites that can act as phytotoxins in times of competition and stress. Empetrum nigrum and Racomitrium spp. are common unpalatable species in Iceland, and previous research indicates that these plants may have allelopathic effects on competing plants, inhibiting germination, growth, and survival. The primary goal of the present study was to determine whether E. nigrum and Racomitrium spp. are allelopathic plants in their Icelandic habitats. More specifically, to capture the allelopathic effects in these plants' natural habitat, both field and laboratory experiments were performed. For the laboratory experiment, sampling of plant and soil material took place at two study sites in the northern highlands of Iceland, one within the active volcanic zone, Þeistareykir, and the other outside it, Auðkúluheiði. Bioassays were used to investigate how E. nigrum leaves and Racomitrium spp shoots as well as the soil beneath E. nigrum or Racomitrium spp. affected the germination of two common vascular plants, Festuca richardsonii and Bistorta vivipara, as well as the root growth of F. richardsonii. The field experiment was carried out in Auðkúluheiði, where the effect of E. nigrum on germination and seedling survival of F. richardsonii was examined in a removal experiment. According to the results of the laboratory experiment, the leaves and soil beneath E. nigrum as well as the soil beneath Racomitrium spp inhibited the germination of the two vascular plant species. In contrast, the Racomitrium spp shoots did not demonstrate any inhibitory effects. Allelopathic effects are the most likely mechanism accounting for these inhibitory effects but further ...
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