The causes of local diversity and composition remain a central question in community ecology. Numerous studies have attempted to understand community assembly, both within and across trophic levels. However, little is known about how community assembly aboveground influences soil microbial communities belowground. We hypothesized that plant establishment order can affect the community of arbuscular mycorrhizal fungi (AMF) in roots, with the strength of this effect dependent on both host plant identity and neighboring plant identity. Such priority effects of plants on AMF may act through host-specific filters of the initial species pool that limit the available pool for plants that established second. In a greenhouse experiment with four plant hosts, we found that the strength of the priority effect on AMF communities reflected both host plant characteristics and interactions between host and neighbor plant species, consistent with differential host specificity among plants. These patterns were independent of plant biomass and root colonization. Functional studies of AMF associated with a wide array of host plants will be required to further understand this potential driver of community dynamics.