Oxalic acid secretion and extracellular oxalate regulation by brown rot wood decay fungi

• Published in: Phytopathology Vol. 96; no. 6; p. S182
• Main Authors: Schilling, J S, Jellison, J
• Format: Journal Article
• Language: English
• Published: 01.06.2006
• ISSN: 0031-949X

Brown rot fungi depolymerize wood non-enzymatically by combining iron (II) and hydrogen peroxide to produce hydroxyl radicals. We are studying the role of fungal oxalic acid secretion in lowering pH and mobilizing iron because it is unknown if these functions are mechanistic or incidental. We tested for oxalate optimization by subjecting wood pre-treated with 0-100 mM oxalate to several brown rot species. In agar microcosms, brown rot fungi equalized wood pH and oxalate regardless of time-zero level. In soil-block microcosms, however, oxalate catabolism dynamics were more variable between microcosms, suggesting soil effects. Because these same fungi over-produce oxalate when grown on metal-amended agar, we tested effects of soil-relevant forms of Fe, Al, and Cu on these brown rot dynamics. While agar oxalate levels were affected by metal treatments, wood oxalate was equal among treatments despite significant metal translocation into the wood. Our work suggests that brown rot fungi regulate extracellular oxalate during wood decay, and this has implications both on in-service wood preservation and on forest biogeochemistry.