Environmental Heterogeneity Reshapes Arthropod Communities and Overrides Biodiversity Effects on Carrion Decomposition Across the Qinghai-Tibet Plateau

Although arthropods are key agents of detritus decomposition, the extent to which environmental heterogeneity modulates this process through shifts in community composition remains poorly understood, particularly in high-elevation ecosystems. We examined animal-derived detritus (yak carrion) decomposition on the Qinghai-Tibet Plateau, partitioning direct spatial (grassland, shrubland, riverbank and wetland) and temporal effects (July-September) from those mediated by arthropod assemblages. Our results reveal that species richness and abundance varied significantly among habitats and sampling months, with species richness highest in grasslands, particularly in July, whereas abundance peaked in shrublands, especially in September. Multivariate analyses revealed pronounced habitat-level differentiation in arthropod community composition and strong associations with environmental variables, especially vegetation richness. Decomposition rates (K) were substantially higher in grassland and shrubland than in riverbank and wetland habitats, peaking in July for grasslands and in September for shrublands. Structural equation modelling (SEM) revealed that decomposition was directly driven by habitat type rather than indirectly through arthropod richness and abundance, demonstrating that environmental heterogeneity on the Qinghai-Tibet Plateau dominates over biodiversity effects on ecosystem functioning and highlighting the context-dependent nature of arthropod-mediated decomposition.