Complex effects of mammalian grazing on extramatrical mycelial biomass in the Scandes forest‐tundra ecotone

• Published in: Ecology and evolution 2018-01, Vol.8 (2), p.1019-1030
• Main Authors: Vowles, Tage, Lindwall, Frida, Ekblad, Alf, Bahram, Mohammad, Furneaux, Brendan R., Ryberg, Martin, Björk, Robert G.
• Format: Article
• Language: English
• Subjects: Betula nana; Betula pubescens subsp; Betula pubescens subsp. czerepanovii; Biomass; Community composition; czerepanovii; Ecology; Ecosystems; ectomycorrhiza; Ectomycorrhizas; Ekologi; extramatrical mycelia; Forest biomass; Forests; Fungi; Grazing; Herbivores; Herbivory; mountain birch forest; Mycelia; Original Research; Plant communities; Plant populations; shrub heath; Species composition; Thawing; Tundra
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.3657

Mycorrhizal associations are widespread in high‐latitude ecosystems and are potentially of great importance for global carbon dynamics. Although large herbivores play a key part in shaping subarctic plant communities, their impact on mycorrhizal dynamics is largely unknown. We measured extramatrical mycelial (EMM) biomass during one growing season in 16‐year‐old herbivore exclosures and unenclosed control plots (ambient), at three mountain birch forests and two shrub heath sites, in the Scandes forest‐tundra ecotone. We also used high‐throughput amplicon sequencing for taxonomic identification to investigate differences in fungal species composition. At the birch forest sites, EMM biomass was significantly higher in exclosures (1.36 ± 0.43 g C/m2) than in ambient conditions (0.66 ± 0.17 g C/m2) and was positively influenced by soil thawing degree‐days. At the shrub heath sites, there was no significant effect on EMM biomass (exclosures: 0.72 ± 0.09 g C/m2; ambient plots: 1.43 ± 0.94). However, EMM biomass was negatively related to Betula nana abundance, which was greater in exclosures, suggesting that grazing affected EMM biomass positively. We found no significant treatment effects on fungal diversity but the most abundant ectomycorrhizal lineage/cortinarius, showed a near‐significant positive effect of herbivore exclusion (p = .08), indicating that herbivory also affects fungal community composition. These results suggest that herbivory can influence fungal biomass in highly context‐dependent ways in subarctic ecosystems. Considering the importance of root‐associated fungi for ecosystem carbon balance, these findings could have far‐reaching implications. We compared extramatrical mycelial biomass in 16‐year‐old herbivore exclosures and unenclosed control plots at five sites in the Scandes forest‐tundra ecotone, and used DNA sequencing to investigate differences in fungal species composition. We found that mycelial biomass was significantly higher in exclosures at our birch forest sites, whereas at our shrub heath sites, grazer exclosure appeared to have a negative effect on fungal biomass. These results show that herbivory can influence fungal biomass in highly context‐dependent ways in subarctic ecosystems, which, considering the importance of root‐associated fungi for ecosystem C balance, could have global implications.