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
the plant 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 10 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 10 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.
