Extraction and translocation of calcium from gypsum during wood biodegradation by oxalate-producing fungi

Dry rot fungi are a unique group of brown rot fungi, capable of decaying wood at a distance from soil and moisture sources. When degrading wood in the built environment, these fungi are typically observed in contact with calcium (Ca)-containing materials, but it is unclear how or if this association benefits the fungus. In this work, several wood-degrading fungi, including two dry rot species, were cultured for 10 weeks in agar-block microcosms containing spruce heartwood and a Ca treatment. Calcium treatments were gypsum blocks (>99% pure CaSO4) or 2 mM CaCl2 in agar. Controls contained no Ca addition. Scanning electron microscopy and microanalysis confirmed hyphal contact with gyp-board and verified Ca oxalate crystal formation. Cation analysis revealed net Ca enrichment in wood degraded in the presence of gyp-board, including wood degraded by a white rot fungus. Despite wood Ca enrichment in gypsum treatments, wood weight loss and pH were unaffected, while acid-extractable oxalate was often higher. This suggests that Ca extracted from materials by wood decay fungi affects oxalate solubility, but does not necessarily facilitate wood decay. This dynamic should, however, be explored in relation to other building material elements and during incipient decay.