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

Top-down control by nematodes over soil microorganisms – considered stronger over bacteria than 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, high reindeer densities during autumn migration have induced shift into graminoids and 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 hig..., , This file contains densities of nematode trophic groups and families together with soil phospholipids (PLFAs) after four growing seasons of factorial warming and fertilization at two 50-year reindeer grazing intensities. The study site is conducted in Raisduoddar (69°31’29 N, 21°19’16 E; altitude 430–570 m asl), northern Norway.Â