To elucidate the water-conducting pathways in living trees by the dye injection method, suitable sample preparation procedures are needed. We evaluated quantitatively the properties and concentrations of three dyes (acid fuchsin, basic fuchsin and safranin) widely used for this purpose, and determined the optimal conditions required to avoid artifacts after dye injection into the sap stream of Pieris japonica D. Don. Among the dyes tested, an aqueous solution of acid fuchsin at a concentration of 0.1% or more was the most useful for delineating water movement. In non-transpiring stem segments, the vertical movement of acid fuchsin by capillarity and diffusion from the dye injection site was limited. However, acid fuchsin moved rapidly in the horizontal direction by capillarity and diffusion, and most xylem cells were stained within 2 h. A delay of more than 2 h between dye injection and examination of the tissues greatly reduces the precision of the method. Use of the dye injection method without appropriate, well-defined experimental procedures may give rise to misleading information about the functional water-conducting pathway in living trees.

An analysis was made of progressive changes in patterns of cavitation in the sapwood of three species of conifer (Larix kaempferi, Abies sachalinensis, and Picea jezoensis) that were growing in a sub-frigid zone. In all three conifers, all tracheids of the newly forming outermost annual ring were filled with water or cytoplasm during the period from May to August. However, many tracheids in the transition zone from earlywood to latewood lost water in September, presumably through drought-induced cavitation. Cavitated tracheids tended to be continuously distributed in a tangential direction. Subsequently, some earlywood tracheids of the outermost annual ring lost water during the period from January to March. This was associated with freeze-thaw cycles. In the second and third annual rings from the cambium of all three conifers, the lumina of most tracheids in the transition zone from earlywood to latewood contained no water. In contrast, some latewood tracheids near the annual ring boundary and many earlywood tracheids retained water in their lumina. The third annual ring had more cavitated tracheids than the second annual ring. Our observations indicated that cavitation progressed gradually in the tracheids of the conifers and that they were never refilled once cavitation had occurred. The region involved in water transport in conifers did not include the entire sapwood and differed among annual rings.

Compared to trees, little is known about the respiratory characteristics of bamboo, especially culm respiration. In this study, we measured the respiration rates of current year, 2, 3, and above 4-year-old Moso bamboo (Phyllostachys pubescens) culms and examined its relation to culm morphology and anatomical structure. Current year culms had substantially higher respiration rates (1.9 ± 0.46 μmol m^–2 s^–1) compared to older culms (2, 3, and above 4-year-old average: 0.17 ± 0.09 μmol m^–2 s^–1). Culm wood density increased with age, with the concurrent thickening of parenchyma cell walls in the culm tissue. Nitrogen content in the culm tissue decreased with culm age. Both culm wood density and nitrogen content had significant relationships with culm respiration rate. On the other hand, culm height, wall thickness, and circumference did not affect culm respiration rate. Although bamboo culms did not change in size through the year, anatomical changes in the culm tissue that accompanied the aging of a culm affected the respiration. The culm age would have a significant effect on the evaluation of the respiratory characteristics of the bamboo forest. Our results suggested that young culms required a large amount of respiration to grow “inward” as cell wall thickening and also to maintain the relatively large amount of active tissue.