Soil phosphorus (P) drives productivity and floristic composition across tropical forest landscapes, but equivalent links between soil P and tropical forest fauna remain poorly understood. We evaluated soil P as a driver of understorey Coleoptera and epigeal arthropod assemblages across a natural landscape-level soil fertility gradient and at an adjacent site-level P fertilisation experiment in central Panama. A fifth of Coleoptera families in flight-intercept traps (corresponding to 10%-55% [range of values across 10 sites] of all specimens), a third of litter-extracted Coleoptera families (7%-86% of specimens), and almost half of litter-extracted fauna orders (20%-69% of specimens) displayed significant abundance trends across the natural fertility gradient. These responses were not paralleled in the site-level fertilisation experiment, which could be an indication that floristic composition is a proximal driver of arthropod-soil P associations across the lowland tropical forest landscape of central Panama. By revealing the significant, indirect role of soil P in shaping tropical arthropod assemblages, our results highlight the ongoing connection between geological-scale processes and the contemporary ecology of the most diverse group of animals on Earth.