University of Oulu

Stark, S., Väisänen, M., Männistö, M.K., Kühn, J. and Ruess, L. (2023), Long-term grazing intensity by reindeer alters the response of the soil micro-food web to simulated climate change in subarctic tundra. Oikos e09855.

Long-term grazing intensity by reindeer alters the response of the soil micro-food web to simulated climate change in subarctic tundra

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Author: Stark, Sari1; Väisänen, Maria1,2; Männistö, Minna K.3;
Organizations: 1Arctic Centre, University of Lapland, Rovaniemi, Finland
2Ecology and Genetics Research Unit, University of Oulu, Oulu, Finland
3Natural Resources Institute Finland, Rovaniemi, Finland
4Humboldt-Universität zu Berlin, Institute of Biology, Ecology Group, Berlin, Germany
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.2 MB)
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Language: English
Published: John Wiley & Sons, 2023
Publish Date: 2023-08-17


Top–down control by nematodes over soil microorganisms — considered to be stronger over bacteria than over fungi — may dampen microbial responses to global changes in tundra. To test whether large grazers alter the responses of belowground trophic networks to global changes, we employed factorial warming and nitrogen fertilization treatments in adjacent sites with different reindeer grazing intensities for the past 50 years. Lightly grazed tundra is dominated by dwarf shrubs and a more fungal-based microbial community, while in heavily grazed tundra the high reindeer densities during autumn migration have induced a shift into graminoids and a more bacterial-based microbial community. We analysed the soil micro-food web (i.e. the nematode density, trophic structure and species composition) as well as fungal, bacterial and total phospholipid fatty acids (PLFAs) after four growing seasons of warming and fertilization both before and during reindeer migration. We predicted that bacterivore densities are higher and fungivore densities lower under heavy than light grazing (i.e. nematode populations before migration reflect grazing effects via the base of the food web), whereas reindeer migration induces a negative impact on nematode densities under heavy grazing (disturbance by trampling is the driving factor). We further predicted that nematodes negate treatment effects on microbial biomass to a stronger extent in the bacterial-based heavily grazed tundra than in the fungal-based lightly grazed tundra. Fungivore densities were higher under light than under heavy grazing, but nematodes did not respond to trampling. Warming increased fungivores and the fungal PLFAs irrespective of grazing and timing but, under heavy grazing, it increased bacterivores while the bacterial PLFAs remained steady. Fertilization increased carnivores and influenced nematode species composition, diversity and maturity interactively with warming. Our data suggest that large grazers affect tundra soil nematodes via bottom–up effects through microbial community composition and biomass, which in turn may alter the strength of their top–down control over soil bacteria under climate warming.

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Series: Oikos
ISSN: 0030-1299
ISSN-E: 1600-0706
ISSN-L: 0030-1299
DOI: 10.1111/oik.09855
Type of Publication: A1 Journal article – refereed
Field of Science: 1181 Ecology, evolutionary biology
Funding: This work was supported by the Academy of Finland (decision no. 218121 and 130507 to SS).
Copyright information: © 2023 The Authors. Oikos published by John Wiley & Sons Ltd on behalf of Nordic Society Oikos. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.