Department of Plant Ecology, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki 305-8687, Japan.
Tree Physiol. 2010 Aug;30(8):935-45. doi: 10.1093/treephys/tpq025. Epub 2010 Jun 24.
This study compared leaf gas exchange, leaf hydraulic conductance, twig hydraulic conductivity and leaf osmotic potential at full turgor between two drought-deciduous trees, Vitex peduncularis Wall. and Xylia xylocarpa (Roxb.) W. Theob., and two evergreen trees, Hopea ferrea Lanessan and Syzygium cumini (L.) Skeels, at the uppermost canopies in tropical dry forests in Thailand. The aims were to examine (i) whether leaf and twig hydraulic properties differ in relation to leaf phenology and (ii) whether xylem cavitation is a determinant of leaf shedding during the dry season. The variations in almost all hydraulic traits were more dependent on species than on leaf phenology. Evergreen Hopea exhibited the lowest leaf-area-specific twig hydraulic conductivity (leaf-area-specific K(twig)), lamina hydraulic conductance (K(lamina)) and leaf osmotic potential at full turgor (Ψ(o)) among species, whereas evergreen Syzygium exhibited the highest leaf-area-specific K(twig), K(lamina) and Ψ(o). Deciduous Xylia had the highest sapwood-area-specific K(twig), along with the lowest Huber value (sapwood area/leaf area). More negative osmotic Ψ(o) and leaf osmotic adjustment during the dry season were found in deciduous Vitex and evergreen Hopea, accompanied by low sapwood-area-specific K(twig). Regarding seasonal changes in hydraulics, no remarkable decrease in K(lamina) and K(twig) was found during the dry season in any species. Results suggest that leaf shedding during the dry season is not always associated with extensive xylem cavitation.
本研究比较了两种落叶树种（Vitex peduncularis Wall. 和 Xylia xylocarpa（Roxb.）W. Theob.）和两种常绿树种（Hopea ferrea Lanessan 和 Syzygium cumini（L.）Skeels）在泰国热带干燥森林上层树冠的叶片气体交换、叶片水力导度、嫩枝水力传导率和叶片充分膨压时的渗透势。目的是检验：（i）叶片和嫩枝水力特性是否因叶片物候而不同；（ii）木质部空化是否是叶片在旱季脱落的决定因素。几乎所有水力性状的变化更多地取决于物种，而不是叶片物候。在物种间，常绿的 Hopea 表现出最低的比叶面积嫩枝水力导度（specific K(twig)）、叶片水力导度（lamina hydraulic conductance, K(lamina)）和叶片充分膨压时的渗透势（osmotic potential at full turgor, Ψ(o)），而常绿的 Syzygium 表现出最高的比叶面积嫩枝水力导度、叶片水力导度和渗透势。落叶的 Xylia 具有最高的边材面积比叶面积嫩枝水力导度，同时具有最低的胡伯值（边材面积/叶面积）。在旱季，落叶的 Vitex 和常绿的 Hopea 表现出更负的渗透势和叶片渗透调节，同时具有较低的边材面积比叶面积嫩枝水力导度。关于旱季的水力变化，在任何物种中，旱季期间 K(lamina)和 K(twig)均未出现明显下降。结果表明，叶片在旱季脱落并不总是与广泛的木质部空化有关。
