Temporal changes in the elemental composition of Rhizopogon rhizomorphs during colonization of patches with fresh organic matter or acid-washed sand

A laboratory experiment was performed to estimate the elemental composition of rhizomorphs of an ectomycorrhizal (EM) fungus growing in a patchy environment. Successive samples of Rhizopogon rhizomorphs, located adjacent to patches with organic matter or patches with acid-washed sand, were taken over a period of 45 d. The mass per unit area was analyzed with scanning transmission ion microscopy (STIM), and the elemental content of elements heavier than Mg were analyzed with particle induced X-ray emission (PIXE). Rhizomorphs associated with the organic matter on average were three times heavier per unit area than rhizomorphs associated with sand. The Ca concentration (mg g(-1)) increased in rhizomorphs adjacent to patches with sand, while it decreased in rhizomorphs adjacent to patches with organic matter. Fe concentration was higher in rhizomorphs adjacent to patches with sand. We concluded that the EM fungus responded to the organic matter by producing larger rhizomorphs, rather than increasing the concentration of elements in the rhizomorphs, to improve the transport of elements to the roots. The elemental composition of rhizomorphs varied considerably over time, and the accumulation of Ca in rhizomorphs in the sand-filled compartments could be the effect of acropetal flow of solutes from the plant roots toward the mycelial front.