Origin and hydrodynamics of xylem sap in tree stems, and relationship to root uptake of soil water.

Although 10 years have passed since Japan's Fukushima nuclear accident, the future radiation risk from Cs contamination of wood via root uptake is a serious concern. We estimated the depth at which the roots of evergreen coniferous sugi (Cryptomeria japonica) and broadleaf deciduous konara (Quercus serrata) trees actively take up soil water by using positive δD values from the artificial DO tracer and seasonal changes in the δO values of soil water as a natural environmental tracer. We compared the tracer concentration changes in xylem sap with those in the soil water and ascertained that both tree species primarily took up water from a depth of 20 cm, though with mixing of water from other depths.