Weathering of Limestone, Marble, and Calcium Phosphate by Ectomycorrhizal Fungi and Associated Microorganisms

Abstract

Ectomycorrhizal fungi and their associated microorganisms were tested for their ability to weather Limestone, marble, and calcium phosphate using a plate method. Degradation of these rock materials led to production of clear zones around the microbial colonies. A displacement method also was used to test selected microorganisms for their capacity to release calcium from the insoluble rock materials. Most of the fungi tested were ectomycorrhizal and associated with Douglas-fir (Pseudotsuga menziesii) or Scots pine (Pinus. sylvestris). Most of the associated microorganisms tested were isolated from the mycorrhizal sporocarps, Douglas-fir ectomycorrhizas, or red alder (Alnus rubra) nodule surfaces. Rhizopogon vinicolor, Suillus bovinus, Hysterangium setchellii, a Rhizopogon-associated Penicillium sp. and a yeast were able to degrade limestone, marble, and calcium phosphate, as were 4 fluorescent pseudomonads and 3 Azospirillum isolates associated with R vinicolor and Douglas-fir ectomycorrhizas. As a result of the rock solubilization, the pseudomonads released significantly more calcium than did other microorganisms. A possible role of a microbially mediated weathering process in nutrient cycling in rhizosphere ecosystems is discussed.