The ant-plant Hirtella physophora (Chrysobalanaceae), the ant Allomerus decemarticulatus (Myrmicinae) and an Ascomycete fungus, Trimmatostroma sp., form a tripartite association. The fungus improves nutrient uptake by the host plant, but hitherto it has been unclear whether it has an indirect or a direct role in transferring nutrients to the plant.
Identification of hyphae inside stem tissue and a stable nitrogen isotope tracer experiment combined with NanoSIMS imaging reveals that 15N-enriched cells are not diffuse. Leroy et al. show that in this ant-plant system a fungus actively transfers nitrogen from a 15N-labelling solution to the plant’s stem tissues, suggesting that the fungus may play a role in transporting nutrient-derived ant waste. The complex trophic structure of ant-plant interactions is shown to rely upon the presence of the fungus. The study provides insight into the potentially important nutritional aspects and tradeoffs involved in myrmecophyte–ant mutualisms.