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.

Horizontal, but not vertical, biotic interactions affect fine‐scale plant distribution patterns in a low‐energy system

“…in Pajunen et al's (2011) study, several were in common with the species in this study, confirming our result that Betula may strongly interact with co-occurring species (see also Olofsson 2004). Again, some of the species included in this study have been previously found to be sensitive to the presence of Empetrum (including Deschampsia flexuosa, Vaccinium myrtillus, V. vitis-idaea, and Solidago virgaurea; Nilsson et al 2002, Bra˚then et al 2010. Again, some of the species included in this study have been previously found to be sensitive to the presence of Empetrum (including Deschampsia flexuosa, Vaccinium myrtillus, V. vitis-idaea, and Solidago virgaurea; Nilsson et al 2002, Bra˚then et al 2010.…”

Contrasting effects of biotic interactions on richness and distribution of vascular plants, bryophytes and lichens in an arctic–alpine landscape

“…Nilsson and Zackrisson 1992;Aerts 2010) and distribution of individual species (le Roux et al 2013a), and on community composition (le Roux et al 2014). These effects are driven via the negative impacts stemming from E. hermaphroditum's intense resource competition and allelopathy (Tybirk et al 2000;Bråthen et al 2010), but also via positive effects related to amelioration of harsh environmental conditions (Carlsson and Callaghan 1991). However, the mainly positive relationships in individual SDMs between lichens and E. hermaphroditum were unexpected, particularly given the general negative impact of vascular plants on lichen performance (Cornelissen et al 2001).…”

Outcomes of biotic interactions are dependent on multiple environmental variables

“…Bråthen et al. ). Nonetheless, it appears that geomorphological disturbance affects the reproductive effort of all species, specifically with higher disturbance levels generally associated with an increasingly positive effect of Empetrum on neighbouring individuals.…”

“…; Bråthen et al. ), including studies of its interaction with other species (e.g. Carlsson & Callaghan ; Bråthen et al.…”