Climate-dependent variations in plant and nematode functional traits following shrub encroachment

• Shrubs increased taxonomic and functional diversity of plant and nematode communities. • Shrub and climate jointly modulate nematode trophic structure and enrichment footprint. • Shrubs reduced the relationship between plant traits and nematode traits in a pattern of functional decoupling. Current climate change and anthropogenic activities are causing shrub encroachment, affecting biodiversity and ecosystem functioning. Shrub and their associated herbaceous plants and soil organisms will asynchronously colonize the new range, shaping different above and belowground relationships along climate gradients. With this work we quantify the functional linkage of plant and nematode communities in functional diversity and traits between shrubs and open spaces at 63 sites spanning broad climatic gradients on the Qinghai-Tibet Plateau. Shrub and climate interaction reshuffles herbaceous plant and nematode diversity and their function. Shrubs increased nematode taxonomic and functional diversity with increasing precipitation and temperature, but such shrub effects on plant diversity were independent of the climatic gradient. Shrub, precipitation, and temperature jointly modulate nematode traits, but have little effects on herbaceous plant traits. Shrubs increased nematodes with longer generation time, larger body mass, and at higher trophic levels, enhancing the metabolic footprint of soil communities; stronger modification on soil food webs and enrichment footprints amplified with increasing precipitation and temperature. Shifts in plant traits were associated with nematode C-P value and trophic structure, while Shrubs reduced the linkage between plants and nematodes in functional traits. Our study demonstrates that climate modulates the facilitative shrub effects on biodiversity and its functions, but points to the functional decoupling of plants and nematodes to environment shifts that may delay nutrient cycle and impact ecosystem functioning.