Abstract: Aims The biodiversity-ecosystem function relationship is a prominent research topic within ecology. In the context of global environmental changes, biodiversity loss may constrain ecosystem functioning. Most existing studies focus on diversity effects on individual functions (e.g., productivity, carbon sequestration, etc.) or ecosystem multi-functionality (EMF), while overlooking the interactions among different ecological functions - a phenomenon quantified as ecosystem coupling. To date, it remains elusive how diversity changes impact ecosystem coupling and the relationships between EMF and ecosystem coupling. Methods Using standardized field surveys across 40 sampling sites across the Tibetan alpine grasslands, we explored the large-scale patterns of ecosystem multifunctionality and ecosystem coupling, and their relationships with plant diversity. Important findings The EMF exhibited highly spatial heterogeneity, while ecosystem coupling showed less variation at the regional scale. Meanwhile, no significant correlation was observed between EMF and ecosystem coupling. The EMF was significantly correlated with climatic factors, plant diversity, and soil properties, whereas ecosystem coupling remained insensitive to variations in both biotic and abiotic drivers. These results reveal a widespread decoupling between EMF and ecosystem coupling at the large scale, not supporting the notion that higher EMF associated with stronger ecosystem coupling based on controlled experiments. Our findings provide new insights into the relationship between biodiversity and ecosystem functions, and also lay a theoretical base for achieving the national strategy of "integrated management of mountains, waters, forests, farmlands, lakes, grasslands and deserts " via biodiversity conservation.

Key words: ecosystem multifunctionality, ecosystem coupling, biodiversity, alpine grasslands