‘Dry rot’ fungi are a unique group of brown rot fungi that can degrade wood away from ground contact where other fungi fail to colonize. Successfully occupying this niche is partially due to efficient water and nutrient transport, but mobilizing elements, notably calcium (Ca) and iron (Fe), from adjacent building materials has also been implicated in their success. Here we report a series of trials with Serpula himantioides (previously ATCC 36335 S. lacrymans) degrading blocks in the presence or absence of Ca-rich gypsum (aka. drywall, plasterboard), using weight-loss as a measure of decay success. In previous work, pure gypsum did not facilitate dry rot in optimal growth conditions, but it was unclear if moisture or Fe-impurities could alter this dynamic. Commercial drywall was tested in a standard ASTM soil-block trial with spruce blocks and this Serpula wild-type isolate. Gypsum was also made from >99% pure CaSO4 and added in a sand-block trial with variable moisture. Finally, FeSO4 was used to amend gypsum to various Fe contents and the hardened material added to microcosms where spruce was decayed with no external Fe source. Weight-loss in blocks decayed in each experiment was statistically equal between treatments with and without the building material. These results corroborate previous findings, although this dynamic should be tested with other Serpula isolates and in an in-service trial to determine the role of building materials in dry rot.

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