Conclusions
Among the species examined, increasing CWR appears to indicate differential utilization of stored water in relation to variation of xylem structure, thereby providing insight into the interspecific responses of tree species to drought.
Methods
To fill the existing knowledge gap, we excised twigs of Abies firma (Japanese fir, conifer), Cercidiphyllum japonicum (katsura tree, diffuse-porous) and Quercus serrata (konara oak, ring-porous) to quantify interspecific variation of water transfer in xylem corresponding with increasing cumulative water release (CWR) using micro x-ray computed tomography and cryo-SEM.
Results
For all species studied, the main components of water storage within the operating range of water potential were not living cells but cavitation release and capillaries. Abies firma maintained water in the earlywood-like cells, for possible maintenance of the transpiration stream. Cercidiphyllum japonicum maintained water in its vessels over 200 kg m-3 of CWR, while Q. serrata lost most of its water in vessels with increasing CWR up to 100 kg m-3 . Cercidiphyllum japonicum exhibited a higher water storage capacity than Q. serrata. Under high CWR, narrow conduits stored xylem water in C. japonicum and imperforate tracheary elements in Q. serrata. Conclusions: Among the species examined, increasing CWR appears to indicate differential utilization of stored water in relation to variation of xylem structure, thereby providing insight into the interspecific responses of tree species to drought.