Cellular-level water distribution in the green wood of Eucalyptus trees cultivated in Japan

Understanding xylem water distribution is essential for evaluating both the physiological traits of trees and their characteristics related to wood processing. This study examined cellular-level water distribution in the green wood of nine trees from four Eucalyptus species— E. saligna, E. piperita , E. elata, and E. smithii —cultivated in Japan, using gravimetric measurement, soft X-ray photography, and cryo-scanning electron microscopy (cryo-SEM). All examined trees contained large amounts of water, with an average of 88% of cell lumina filled. Notably, vessel water distribution in the heartwood varied within and among individual trees, while imperforate tracheary elements (ITEs) were consistently filled with water throughout the sapwood and heartwood. Cryo-SEM observations further revealed that ITEs surrounding vessels and small vessels arranged in periodic tangential bands tended to retain more water than other cells of the same type. These findings suggest that the hydration status of vessels contributes to variation in water distribution; ITEs serve as stable water reservoirs; and the morphology of these cells influences their property of water retention in Eucalyptus xylem. This knowledge provides foundational insights into tree physiology and wood properties of Eucalyptus species, such as fast growth, environmental adaptability, and vulnerability to cell collapse.