Volcanic soils alleviate the allelopathic capacity of Empetrum nigrum in degraded tundra ecosystems

Land degradation due to unsustainable land use is of major concern worldwide, and recovery is often slow. A potential mechanism behind slow recovery of degraded ecosystems is the retarding impacts of allelopathic plant species on the establishment of species that might facilitate the recovery process. However, the strength of the retarding impact may depend on soil type. In this study, we investigated the potential role of an abundant, evergreen, and allelopathic dwarf shrub, Empetrum nigrum, in trapping tundra ecosystems in a degraded state in Iceland after centuries of unsustainable land use. We first run a series of bioassays to assess the potential allelopathic legacy effects of the Empetrum-associated volcanic soils (Andosol and Vitrisol) on seed germination and root elongation of the common grass species Festuca richardsonii in comparison with Empetrum-associated non-volcanic Histosol and Podzol soil types. Then we assessed the Empetrum leaf-soil interactions for all soil types using leaves from a degraded site in Iceland. We found no potential allelopathic legacy effects of Empetrum associated with volcanic soils, whereas the non-volcanic soils negatively impacted Festuca root elongation. Empetrum leaves alone affected both seed germination and root elongation. These effects were strongly alleviated by the volcanic soils, but not by the non-volcanic soils. We conclude that abundant allelopathic plant species may significantly contribute to trapping tundra ecosystems in a degraded state, but the strength of this trapping mechanism depends on the soil environment.