Interfering with neighbouring communities: allelopathy astray in the tundra delays seedling development

1. Altered species composition caused by environmental and climatic change can affect the transfer of plant residues among communities. Whereas transferred residues are typically considered a resource in recipient systems, residues of allelopathic species may instead cause interference. 2. Evergreen dwarf shrubs, specifically the allelopathic species Empetrum nigrum are increasing in abundance in response to a warming climate. Empetrum has small, evergreen leaves that can be transferred to other communities when withered and lost from the plant. 3. We hypothesize that Empetrum can have allelopathic effects in the recipient communities of the withered leaves. We call this allochthonous allelopathy as opposed to autochthonous allelopathy, which is well documented in communities where it grows. 4. We measured influx of allochthonous Empetrum leaves onto snow-covered snowbeds, where they are easily identified within the debris. Next, we compared the bioactivity of allochthonous withered leaves with that of green Empetrum leaves. Finally, we conducted an experiment testing the germination and seedling growth of ten tundra species in snowbed soil supplemented with no (control) and three densities of allochthonous Empetrum leaves. 5. We found Empetrum leaves to be common on the snow cover of snowbeds. We found Empetrum leaves collected on snowbeds to be as bioactive as green leaves. Finally, we found forb species to have reduced germination and all ten species to have delayed seedling development when growing in snowbed soil supplemented with withered Empetrum leaves. Seedlings under the control treatment were 2.3 times longer and had 3.2 times more leaves in comparison to seedlings grown under the strongest allochthonous leaf treatment. 6. Results from our study imply that Empetrum is allelopathic in recipient systems of its allochthonous leaves. The abundant nature of Empetrum in the tundra, suggests that allochthonous allelopathy is a common phenomenon, causing biotic stress in snowbeds and potentially other parts of the tundra. Exemplifying the ability of a plant to interfere in neighbouring communities, our study demonstrates a plant trait that may provide insight to other study systems.A readme-file accomplishes description of all the variables that are provided in four different datasets: 1 - counts of Empetrum nigrum leaves on snowbeds. 2 - bioassays on both fresh and withered leaves of Empetrum nigrum along with their content of secondary metabolites. 3 - data on germination of a set of species exposed to withered leaves of Empetrum nigrum in soil. 4 - data on seedling growth of a set of species exposed to withered leaves of Empetrum nigrum in soil. A link to a fifth dataset (abundance data of Empetrum nigrum) that is used in the related paper is also provided here