For saxicolous (rock-dwelling) mosses, the only
feasible sources are dust and precipitation (Rieley et al.
1979), especially for potassium (Bates 1976), although
Hébrard et al. (1974) demonstrated the ability of Grimmia
orbicularis to obtain radiolabelled 90Sr from an artificial
rock. For pleurocarpous taxa and taxa living in the forest,
the atmosphere (dust and precipitation) is generally
considered to be the major nutrient source (Brown 1982),
but as we shall see, this may not be the whole story.