Belowground facilitation and trait matching: two or three to tango?

High biodiversity increases ecosystem functions; however, belowground facilitation remains poorly understood in this context. Here, we explore mechanisms that operate via ‘giving–receiving feedbacks’ for belowground facilitation. These include direct effects via root exudates, signals, and root trait plasticity, and indirect biotic facilitation via the effects of root exudates on soil biota and feedback from biota to plants. We then highlight that these two- or three-way mechanisms must affect biodiversity–ecosystem function relationships via specific combinations of matching traits. To tango requires a powerful affinity and harmony between well-matched partners, and such matches link belowground facilitation to the effect of biodiversity on function. Such matching underpins applications in intercropping, forestry, and pasture systems, in which diversity contributes to greater productivity and sustainability. Belowground facilitation is a vital mechanism underlying ecosystem function in diverse plant communities.A bottleneck to linking theory to application is that interspecific belowground facilitation processes are incompletely understood.Here, we explore direct and indirect facilitation, which requires matching specific belowground responses between the facilitated species and the facilitator.Understanding and integrating the processes of interspecific facilitation helps to design sustainable diverse plant communities with compatible ecosystem functions.