Shrub alters the spatial patterns of nematode taxonomic and functional diversity on the Qinghai-Tibet Plateau

Shrub effect with climate change is known to alter alpha diversity of organism groups at the taxonomic level, but how it influences the beta diversity of soil organisms, particularly functional level, remains poorly understood. Here, we investigated the abundant nematode fauna to assess the shrub effects on alpha and beta diversity at both taxonomic and functional level in sites on the Qinghai-Tibet Plateau. We collected three functional traits (i.e., diet, body mass and life-history) associated with resource acquisition, dispersal ability, reproduction and the rate of nutrient utilization. We calculated the functional alpha and beta diversity of nematode communities under shrubs and open spaces using kernel density n-dimensional hypervolumes and combined it with taxonomic diversity to disentangle the spatial patterns and community assembly of nematode communities. Shrubs significantly increased taxonomic richness, but not functional richness. However, shrubs reshaped broad-scale nematode functional richness and ecological indices along climatic gradients. Shrubs significantly decreased the taxonomic and functional beta diversities of nematode communities, generating biota homogenization. The parallel changes of taxonomic and functional beta diversities were driven by distinct processes. Replacement dominated taxonomic beta diversity variation, while richness difference dominated functional beta diversity variation. Our findings show that shrubs were able to filter functional traits and limit the dispersal of species assemblages that exhibit such traits, thus causing taxonomic and functional homogenization of soil nematodes on the Qinghai–Tibet Plateau. Our findings advance understanding of the spatial patterns of belowground communities for taxonomic and functional aspects.