The Effects of Nitrogenous Compounds on Decay of Wood by Soft-Rot Fungi

Abstract

The amino acids in the sapwood of Fagus sylvatica L., Pinus sylvestris L. and Tilia europaea L. were investigated. The amino acids were identified and quantified in three sections; those present as free amino acids, those bound in soluble proteins and those bound in insoluble protein, The amino acid content of the soft-rot organism, Chaetomium globosum Kunze ex Fr., was also determined and found to be similar in amino acid range and ratio, but lower in magnitude than the timbers. The in vitro ability of three soft-rot fungi and one Basidiomycete to grow and produce cellulase when amino acids were supplied as a nitrogen source was investigated. The fungi were found, in general, to produce greatest growth and cellulase production in the presence of aspartic acid and glutamic acid, the two amino acids found to be most abundant in the sapwood of timbers investigated. A humidity chamber technique was employed to study soft-rot decay of wood. This enabled pure fungal cultures to be used to inoculate the wood and may be considered to simulate conditions which result in soft-rot decay of wood not in ground contact. Fungal spore suspensions were used to inoculate wood blocks which had received additional levels of inorganic or organic nitrogen. The criteria used to assess decay were weight loss and loss of bending strength. Bending strength was measured on a tensometer with specially designed three-point loading jaws. Strength loss and weight loss were closely correlated in decay tests with Chaetomium globosum but in experiments with Trichoderma viride Pers. ex Fr. and Alternaria tenuissima (Fr.) Wiltsh. correlation was apparent only at the highest weight losses. The addition of organic nitrogen to wood, as aspartic or glutamic acid, was found to increase decay by Chaetomium globosum to a greater extent than the addition of inorganic nitrogen.