Effect of Soluble Nutrient Content in Wood on its Susceptibility to Soft Rot and Bacterial Attack in Ground Test

Summary The objective of the study was to investigate whether soluble sugars and nitrogenous compounds in wood have an impact on susceptibility of wood to decay in ground contact, which is important in the field of test methodology and standardization. Kiln drying of Scots pine planks caused a distinct gradient of low-molecular weight (LMW) sugars and nitrogenous compounds in the 0–2 mm zone at the surface of the timber, whereas the deeper zones had constant and low contents of soluble substances. Strips, containing different content of soluble nutrients, were cut and exposed in two types of soil; the former one being rich in soft rot fungi, the latter one being rich in soft rot fungi and bacteria. The strips rich in nutrients showed an average of 16 % of mass loss whereas samples poorer in nutrients were less affected (8–9 %) after 120 days of exposure in the soil rich in soft rot fungi. A pure culture test with the soft rot fungus Phialophora mutabilis confirmed the above-mentioned observation. The result is in favour of taking samples with approximately equal content of soluble nutrients to decrease the variability of test results, e.g., mass losses. The garden compost, rich in both soft rot fungi and bacteria, caused severe mass loss (40–48 %) of the strips after 120 days of exposure. No difference in the mass losses of the samples was measured. The choice of test soil as well as the nutrient status of the samples can lead to completely different results and, consequently, conclusions.