Enhanced water uptake in the longitudinal direction by shiitake mycelium in shiitake cultivation logs: increase in effective diffusion coefficient based on mass of liquid water uptake

In the cultivation of shiitake mushrooms (Lentinula edodes), the farmer needs to know the time needed to water in order to adjust the water content of the logs. In this study, six test logs (Quercus serrata, diameter of 38–48 mm, length of 110–118 mm) were used, of which some were dried, some had shiitake mycelia grown on them, and some had mold generated on them. Liquid water was supplied to the test logs by placing the longitudinal direction of the test logs along the line of gravity and immersing the bottom of the test logs in water. Water uptake mass of the test logs was measured for 20 h. The effective diffusion coefficient, D_eff, was calculated from the change in time of the water uptake mass using Fick's diffusion law. The D_eff of test logs in which shiitake mycelium grew were 1.5–3.4 × 10^–8 m²/s, and the values were 2.4–4.7 times higher than that for the dried log. On the other hand, the D_eff of the moldy logs were 6.7–9.7 × 10^–10 m²/s, which was 0.058–0.081 times that of dry test logs. Based on observation of water penetration into logs by magnetic resonance imaging (MRI) and an optical microscope, it is believed that the driving force behind liquid water rising in the longitudinal direction in the test log is the capillary force acting on a three-phase interface consisting of the inner wall surface of the vessel, liquid water and air.