Abstract: Aims Nematodes are an important component of below-ground communities and play a crucial role in maintaining ecosystem structure and function. Global environmental changes, such as shrub encroachment and nitrogen deposition, have become important drivers of community structure and function. The interactions between different environmental factors together affect biodiversity, but the effects of the interaction between shrub encroachment and nitrogen deposition on soil nematode functional diversity remain unclear. Methods In this study, we conducted field control experiments of shrub removal and nitrogen addition on the eastern edge of Qinghai–Tibetan Plateau. We used kernel density n-dimensional hypervolumes to calculate the functional diversity of nematode communities and to explore the response of nematodes to shrubs, nitrogen deposition and their interactions. Important findings Shrubs significantly increased nematode taxonomic and functional diversity, while nitrogen addition mitigated the positive shrub effects on functional diversity. Shrubs significantly increased the proportion of herbivore, bacterivore, and fungivore nematodes, while decreasing the proportion of predator nematodes. Moreover, nitrogen addition had a little effect on nematode community composition but exacerbated the positive effects of shrub on lower trophic level nematodes and the negative effects on higher trophic level nematodes. Correlation and RDA analyses indicated that plant biomass and soil moisture were key factors driving nematode community composition and functional traits. In the context of future nitrogen deposition and shrub encroachment, nematode functional diversity becomes more similar, but nematode function tends to specialize in different environments.

Key words: soil nematode, functional diversity, functional trait, shrub effect, nitrogen addition, Qinghai–Tibetan Plateau