This study investigated the effect of root disease symptoms on the hydraulic conductivity of symptomatic Douglas-fir and grand fir root segments. The fungi involved include Heterobasidion annosum, Armillaria ostoyae, Inonotus tomentosus, Phaeolus schweinitzii, Phellinus weirii and Leptographium wagnerii. Root segments were excavated from Douglas-fir or grand firs lacking aboveground symptoms. Flow rate through root segments was measured by perfusing the root segments with 10 mM oxalic acid and weighing the flow periodically until it stabilized. Hydraulic conductiviti was computed from the flow rate, the segment length, and the pressure forcing the liquid through the segment. Root segments with staining had a 30% reduction in root hydraulic conductivity when compared with asymptomatic roots; root segments with decay had an 80% reduction. More than 420m of roots were examined from an area of about 20m2; 76% had symptoms of root disease. The prevalence of symptoms and the drastic reduction in root hydraulic conductivity suggest Douglas-firs and grand firs could experience root disease-caused moisture stress in the early stages of root infection.
