SOFT-ROT FUNGAL DEGRADATION OF LIGNIN IN 2700-YEAR-OLD ARCHAEOLOGICAL WOODS

Soft-rot fungal degradation of archaeological wood was investigated by comparing the micromorphological characteristics, elemental compositions and monomeric and dimeric phenols derived from CuO oxidation of lignins in degraded boxwood, maple, juniper and pine woods from Tumulus MM, Turkey, thought to be the ancient tomb to King Midas dated 2700 years before present (BP). Chemical compositions of these soft-rotted archaeological woods were compared to those of modern undegraded counterparts and to those of contemporary white- and brown-rotted woods. The degraded angiosperm woods showed Type 1 (cavity) and Type 2 (erosive) forms of soft-rot, whereas the degraded gymnosperm samples exhibited only Type 1 decay. All soft-rotted woods contained higher weight percentages of ash and nitrogen than their fresh counterparts. Polysaccharides were preferentially attacked by soft-rot fungi as indicated by decreased atomic ratios of hydrogen/carbon in all degraded woods and lower atomic ratios of oxygen/carbon in remnant boxwood, maple, and pine woods. In addition, soft-rot fungi extensively attacked lignin as evidenced by the lower carbon-normalized yields of lignin monomers from most degraded samples. All soft-rotted woods had elevated acid/aldehyde ratios indicative of oxidative microbial degradation of remnant lignin sidechains. Soft-rot degradation resulted in greater carbon cross-linking of the remnant lignin and enrichment of ring-ring dimers in the degraded angiosperm samples, indicating preferential attack of sidechain-linked structures within the lignin polymer. While soft-rot fungi share some degradative characteristics with both white- and brown-rot fungi, the physical and chemical effects of soft-rot degradation are unique.