Ecosystem disturbance reduces the allelopathic effects of Empetrum hermaphroditum humus on tundra plants

Abstract

Question: Do naturally occurring ecosystem disturbances interfere with allelopathic effects and alleviate growing conditions for plants typical of more productive ecosystem states? Location: An unproductive tundra ecosystem in Northern Fennoscandia. Methods: We designed a factorial phytotron experiment to monitor the growth of seedlings of two herbaceous species in undisturbed and disturbed humus of the dominant dwarf shrub Empetrum hermaphroditum, which releases allelopathic substances that accumulate in soil over time. Herbivore defecation and wildfire are two major ecosystem disturbances likely to alleviate effects of these allelopathic substances. Humus and seeds of herbaceous species were sampled from Empetrum-dominated heaths. Disturbance effects on humus were simulated by adding reindeer faeces and by low-severity burning. Results: The concentration of the allelopathic substance batatasin-III in Empetrum humus was 0.32±0.16 (SE) μg g−1, which is similar to previous reports from boreal areas. Reindeer faeces addition and burning treatments to Empetrum humus caused three- and five-fold increases in growth of the herbaceous species Avenella flexuosa and Solidago virgaurea respectively. Changes in soil chemistry caused by the disturbance, i.e. increased pH and nutrient availability, likely interfered with allelopathic effects and improved conditions for growth. Conclusions: Humus from Empetrum-dominated tundra areas is infertile for seedlings of local herbaceous plants. Simulated herbivore defecation and wildfire can alleviate this infertility. Based on our results, we discuss the potential role of these naturally occurring disturbances in switching vegetation composition from Empetrum to herbaceous dominance, i.e. from an unproductive to a more productive tundra ecosystem.