Soil invertebrates mediate the relationship between plant communities and soil biogeochemistry. The traits of soil invertebrates, including body stoichiometry, growth rates, feeding choices, and phenology, influence organic matter processing rates and whether it remains in or leaves the soil system. Plants also shape the abundance, species composition, and diversity of soil invertebrate communities and food webs via the quantity and chemistry of their above- and belowground litters. Consequently, plant and soil invertebrate communities interact during the development of terrestrial ecosystems and together determine decomposition, nutrient cycling, carbon storage, and other emergent properties. At the same time, environmental changes, such as pollution and climate change, are reducing invertebrate diversity and abundance globally, destabilizing food webs. The role soil invertebrates play in plant-soil interactions is recognized but poorly defined in soil biogeochemical dynamics. As such, soil invertebrates are the new “black box” of soil ecology. In this session, presenters will explore the effects of plant communities on the soil invertebrates beneath them and highlight the consequences of soil invertebrate community composition and food web dynamics for soil biogeochemistry.