Role of Fungal Mycelium in the Formation of Carbonate Concretions in Growing Media—An Investigation by SEM and Synchrotron-Based X-Ray Tomographic Microscopy

Soil fungi can facilitate calcification. Mushroom Morchella sp . mycelium induced the formation of carbonate concretions on the surface of an organic-based growing media amended with sand and ground limestone. According to SEM observation and X-ray-tomographic microscopy a dense mycelial network induced calcification. The CaCO3 content of concretions (⊘: 0.3–1.5 cm) was found to be at 30%. Microsparitic calcite cemented the pores between the sand grains forming a dense clogging microstructure. Besides water uptake by the mycelium, a high evaporation rate and a decrease in pCO2 contributed to the formation of the concretions. Fungal mycelium in the concretions is surrounded by voids indicating that at the surface of the mycelium, calcification is counteracted most probably by the release of organic acids.