- 1Department of Arctic and Marine Biology, UiT - The Arctic University of Norway, Tromsø, Norway
- 2Centre for Microbiology and Environmental Systems Science, University of Vienna, Vienna, Austria
- 3Institute of Microbiology, University of Greifswald, Greifswald, Germany
- 4Arctic Centre, University of Groningen, Groningen, The Netherlands
Climate change affects herbivore populations and their migration patterns and feeding grounds in High-Arctic tundra ecosystems. Knowledge about the ecosystem-scaled impacts of environmental changes in the High-Arctic, including changes in herbivore grazing pressure, requires long-term perspectives and the integration of above- and belowground components.
Here we investigated the effects of grazing geese and reindeer on high-Arctic tundra, by studying the effects of short- (4 years) and long-term (14 y) exclusion of herbivores in situ. Within the Thiisbukta peatland, next to Ny-Ålesund (78.93°N, 11.92°E), Svalbard, 5 replicated high-Arctic wet tundra sampling sectors have been established. Each, at the time of sampling, included 4- and 14-year exclosure plots (Ex-4 and Ex-14), as well as control plots (Hr), where herbivory was not prevented.
Preventing herbivory altered a moss-dominated vegetation (Hr) to a mix of mosses and vascular plants (Ex-4) and a vascular-plant-dominated vegetation (Ex-14). These aboveground changes were reflected belowground and included a significant increase in root biomass and significantly higher contents of lignin derivates in the soil organic matter after the long-term exclusion of herbivores. Additionally, concentrations of inorganic phosphorous and monosaccharides (namely glucose and N-acetyl-glucosamine) were also increased after the long-term exclusion, while soil pH and moisture decreased. To study the effects of these alterations on soil organisms and their complex communities we employed metatranscriptomics, allowing us the simultaneous investigation of soil organisms across domains and kingdoms, ranging from Bacteria, Archaea, and viruses, to protists, Fungi, and other microbial Eukaryotes, to soil meso- and macrofauna community members, including Collembola, Nematoda, Arachnida, Insecta, and other small Metazoa. We observed a substantial, often gradual, re-structuring of the soil communities in the exclosure plots on multiple tropical and functional levels. For example, within the microbial food web, we observed decreased relative abundances of eukaryotic predators (e.g., ciliates) and bacterivorous bacteria (e.g., Myxococcota) after the long-term exclusion of herbivores, while relative abundances of viruses targeting Bacteria increased. Prominent changes in relative abundances of meso- and macrofauna community members after the long-term exclusion of herbivores were decreased relative abundances of Rhabditophora (Platyhelminthes), Monogononta (Rotifera), and Maxillopoda (Arthropoda) and increased relative abundance of Insecta and Arachnida (both Arthropoda). However, among eukaryotic kingdoms, Fungi showed the strongest positive response to the exclusion of herbivores and the subsequent increase of vascular plants. Especially the abundances of mycorrhizal fungi and plant pathogens were increased, coinciding with increased relative abundances of viruses targeting Fungi. Furthermore, with increasing coverage of vascular plants, soil respiration rates increased. At the same time, total microbial biomass did not differ significantly, but the turnover time of microbial biomass was significantly shorter 14 years after the exclusion of herbivores.
Taken together our results suggest that High-Arctic tundra ecosystems with a vascular-plant-dominated vegetation, here caused by changes in herbivore grazing pressure, are characterized by an altered soil food web, facilitating a faster microbial loop and an accelerated decomposition of soil organic matter. Thus, we demonstrated how aboveground changes substantially altered belowground communities and the trophic interactions that control carbon cycling in High-Arctic tundra ecosystems.
How to cite: Söllinger, A., Bender, K. M., Martin, V., Bjørdal, Y., Dahl, M. B., Richter, A., Loonen, M., Svenning, M. M., and Tveit, A. T.: Cascading effects of Arctic tundra herbivory on above- and belowground biomass, soil biogeochemistry, and soil (microbial) food webs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11566, https://doi.org/10.5194/egusphere-egu25-11566, 2025.