The study assessed the distinct role of extractives and lignin content in the natural durability of three tropical hardwoods growing in Mozambique namely ntholo (Pseudolachnostylis maprounaefolia Pax), metil (Sterculia appendiculata K. Schum) and neem (Azadirachta indica). The experiment consisted of exposing control, extracted and delignified wood samples to fungal attack caused by brown rot- (Postia placenta and Gloeophyllum trabeum), white rot- (Trametes versicolor and Pycnoporus sanguineus) and soft rot fungi (Chaetomium globosum and Phia- lophora mutabilis) in controlled environment.
Ntholo had the highest extractive content (4.0%) followed by metil (1.1%) and neem (1.0%). The results show that control wood samples of ntholo are characterised as very durable showing negligible mass loss (1.0-2.5%) against all tested fungi. Neem is moderately durable wood species with mass loss of 15.8% against white rot T. versicolor. The most perishable wood species was metil, which is very sensitive to white rot fungi that caused mass loss of 24.3-29.8%.
After removal of water- and solvent-soluble extractives, ntholo was still very durable, but demonstrated an increased mass loss of 3.9-4.2% caused by the white rot T. versicolor. The decay rate also slightly increased for neem (T. versicolor caused 18.2% mass loss). Since metil is perishable wood species with low content of ex- tractives no significant change in the mass loss after extraction was noted.
Delignification of all species had significantly more pronounced effect on the natural durability of tested species compared to removal of extractives. The white rot fungi were most destructive for ntholo and neem leading to mass loss higher than 40%. P. placenta was found to be the main degrader for metil with mass loss of 51.6%. Results confirm the synergy between lignin and extractives for playing key roles for the natural durability of wood.
Keywords: basidiomycetes, extractives, lignin, natural durability, soft rot fungi
Authors
Sitoe E.
Faculty of Agronomy and Forest Engineering, Eduardo Mondlane, University, Maputo, Mozambique
Uetimane E.
Faculty of Agronomy and Forest Engineering, Eduardo Mondlane, University, Maputo, Mozambique
Jebrane M.
Department of Forest Products, Swedish University of Agricultural Sciences, Sweden
Terziev N.
Department of Forest Products, Swedish University of Agricultural Sciences, Sweden
Daniel G.
Department of Forest Products, Swedish University of Agricultural Sciences, Sweden
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