Soluble nutrient content in wood and its susceptibility to fungal discoloration and decay in above ground and ground tests
O M Caballero, N Terziev
The objective of this comprehensive study was to reveal the impact of soluble nutrients in wood on its susceptibility to fungal discoloration and decay in various tests, which is important for the test methodology and standardisation. Seven tests were carried out including pure culture above and ground contact tests, above ground field test and laboratory ground contact tests. The samples containing soluble sugars and nitrogen were more susceptible to mould discoloration than those poor in nutrients. A laboratory test with the fungus Penicillium brevicompactum predicted well the moulding tendency of the samples in the consequent field test. The samples rich in nutrients showed an average of 16% of mass loss whereas samples poorer in nutrients were significantly less affected (8-9%) after 120 days of exposure in a soil rich in soft rot fungi. A pure culture test with the soft rot fungus Phialophora mutabilis confirmed the above -mentioned observation. Garden compost, rich in both soft rot fungi and bacteria, caused severe mass loss (40-48%) of the samples after 120 days of exposure, but no difference in the mass losses between the samples rich and those poor in nutrients was measured. The content of nutrients was neither related to the mass loss of samples in a soil rich in brown rot fungi, nor in a pure culture test with the brown rot fungus Postia placenta. The nutrient status of samples as well as the choice of test soil can lead to completely different results and, consequently, conclusions. The results are in favour of taking samples with approximately equal content of soluble nutrients to decrease the variability of test results, e.g., mass losses.