Apatite and Orthoclase Forest Fertilization: Insoluble Phosphorus and Potassium Made Available By Ectomycorrhizal Fungi and Associated Bacteria.

Most coniferous trees of the boreal forests are associated with ectomycorrhizal fungi. This association is responsible for supplying host trees with minerals and water while the fungal symbiont receives photosynthates. In boreal forests, most of the mineral base cation nutrients available to the ecosystem originate from bedrock weathering by ectomycorrhizal fungi and associated bacteria. Rock weathering is the result of soil microorganisms dissolving minerals by releasing organic acids and siderophores. The present study sought to investigate the value of apatite and orthoclase as sources of phosphorus and potassium in Picea glauca Moench (Voss) and Pinus banksiana Lamb. stands. Forest floors were amended with apatite and orthoclase at a rate of 650 and 900 g/m² either separately or in combination. Changes in tree growth and nutrition were assessed with dendrometric measurements and foliar analyses. The contribution of selected microorganisms to the weathering of apatite and orthoclase was tested in pure culture; we found both minerals to be readily used as P and K sources by common ectomycorrhizal species when no soluble sources of these elements were supplied. Phosphate solubilizing bacteria have been isolated from the mycorrhizosphere of P. glauca and identified using 16S rRNA gene sequences. Further, mesh bags containing rock phosphate, orthoclase and quartz were incubated in the soils of P. glauca and P. banksiana stands in order to observe the diversity of the fungal communities developing within. The possibility of selective carbon allocation by the plant in response to fungal mineral weathering and bacterial hosting abilities will be discussed.