Mycorrhizal fungi are central to the functioning of terrestrial ecosystems, playing a critical role in ecological processes such as nutrient cycling and carbon storage. Mycorrhizal fungi enhance nutrient uptake by plants, primary productivity, decomposition, and they contribute to organic matter accumulation. This session aims to bring together research investigating the diverse roles and functions of mycorrhizal fungi in forest, grassland, wetland, and other “natural” ecosystems, with a focus on ectomycorrhizal, arbuscular, and ericoid mycorrhizal associations. We will explore how mycorrhizal fungi drive ecosystem functioning in its broadest sense, and how these processes respond to environmental changes, from climate change to management. We welcome contributions from research conducted across all biomes and scales, ranging from the global to petri dish environment, encompassing observational, experimental, and modeling approaches. By fostering discussion and sharing cutting-edge research, this session aims to deepen our understanding of mycorrhizal fungi as mediators of ecosystem function, clarify their ecological importance, and highlight the need for continued exploration in this rapidly evolving field.