Fig. 1

Schematic representation of sample treatment and cryo-scanning electron microscopy/energy-dispersive X-ray spectroscopy (cryo-SEM/EDX) point analysis. a, b Bottles with a Cs solution were attached to a trunk approximately 20 cm above the injection hole, and the Cs solution was injected continuously during a defined period (please see Table 1). c, d, e After the injection, a part of the trunk was frozen by liquid nitrogen and the tree was felled. f, g The xylem region where the Cs solution was injected and its conduit were confirmed by the red color achieved by acid fuchsin staining. h, i A fresh transverse surface of the sample block was smoothly cut by cryostat and subjected to observation and analysis by cryo-SEM/EDX. Several points were selected to be analyzed on a secondary electron image, and the characteristic X-ray of each Cs-Lα peak (4.286 keV) was checked