Association of ectomycorrhizal fungi with decomposed animal wastes in forest habitats: a cleaning symbiosis?

A new tripartite relationship among animals, fungi, and plants, based on formation of ectomycorrhiza and on removal of animal wastes, is described. In forest habitats where animal wastes such as urine or faeces or dead bodies, mainly of mammals, have been deposited, a particular group of fungi form reproductive structures successionally after the apparent decomposition of the wastes. This natural event can be simulated by application to the soil of urea, aqueous ammonia, or nitrogen compounds that release ammonia on decomposition. Both field observations and simulation experiments show that, when these events take place in forests of ectomycorrhizal trees, ectomycorrhizal fungi fruit during the late phase in the succession. Ectomycorrhizas are in fact observed in the soils colonized by these fungi. Among these fungi, Hebeloma spp., Laccaria spp., and a few others colonize commonly in various waste sites, while Hebeloma radicosum colonizes specifically in moles’ deserted middens (latrines) near their nests. The animals involved here as waste depositors or cadavers seem not to feed on the fungi and the plants but may depend on them for cleaning their own habitats, since mycorrhizas should readily remove products derived from wastes. The tripartite relationship described may be viewed as a cleaning symbiosis.