Interactions between soil pH, wood heavy metal content and fungal decay at Norway spruce stands

The incidence of conifer wood decay caused by pathogenic white-rot-fungi in the genus Heterobasidion increases along with increase in soil pH. To clarify factors that influence this relationship, 36 Norway spruce stands that represent a wide range in soil pH and calcium content were surveyed for frequency of H. parviporum caused decay and soil type specific differences in wood composition and fungal growth. Significantly higher concentrations of biotoxic metals were recorded for wood from soils with pH below 4.6 compared to less acidic soils. This finding is coherent with the observed generally higher oxalate concentration in decaying wood in the more acidic stands, as wood decay fungi secrete oxalic acid to detoxify excess metals. The performed in vitro inoculation experiment of wood provided no conclusive evidence that H. parviporum strains from different soil types differ in oxalate production. Further field experiments are warranted to test a hypothesis now raised: soil type-specific differences in accumulation of toxic metals in wood influence wood decomposition rate and fungal spread within and between trees, and thereby also stand decay frequency.