Extraction of potassium and/or magnesium from selected soil minerals by Piloderma

Piloderma is a broad host range ectomycorrhizal fungal genus that may benefit conifer growth through increased soil nutrient availability via enhanced soil mineral weathering. In an in vitro study, we investigated the ability of Piloderma to extract K and/or Mg from three soil minerals commonly found in soils of central British Columbia: biotite, microcline, and chlorite. The growth, hyphal morphology, and chemical composition were compared among Piloderma grown for 110 days in media optimized for fungal growth as well as in media where K and/or Mg were supplied from biotite, microcline, and chlorite. Piloderma grown in treatments with low K showed fibrillar growths, hyphal swellings, and hyphae devoid of ornamentation, possibly indicating nutrient deficiency. Differences were found in growth rates, morphologies, and Mg content in hyphae grown in chlorite and biotite treatments, suggesting that Mg was limiting to the normal growth of Piloderma. Energy dispersive X-ray analysis indicated that Piloderma extracted significantly more K from biotite than from microcline. The high Ca and O content of hyphal ornamentation were mainly composed of Ca-oxalate crystals. The study indicated that K and Mg are essential for vigorous Piloderma growth and that Piloderma may provide more available K to host plant through accelerated weathering of biotite, compared to microcline and chlorite sources. The differences were attributed to the ability of Piloderma to efficiently extract K from the interlayer of biotite. However, the exact mechanism by which Piloderma supplies plant roots with K extracted from biotite is still largely unknown.