title: Seasonal variations of gas exchange and water relations in deciduous and evergreen trees in monsoonal dry forests of Thailand.
abstract: 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.
authors.affiliation: Department of Plant Ecology, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki 305-8687, Japan. atto@ecology.kyoto-u.ac.jp
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ishida
authors.forename: Hisanori
authors.initials: H
authors.lastname: Harayama
authors.forename: Kenichi
authors.initials: K
authors.lastname: Yazaki
authors.forename: Phanumard
authors.initials: P
authors.lastname: Ladpala
authors.forename: Amornrat
authors.initials: A
authors.lastname: Sasrisang
authors.forename: Kanokwan
authors.initials: K
authors.lastname: Kaewpakasit
authors.forename: Samreong
authors.initials: S
authors.lastname: Panuthai
authors.forename: Duriya
authors.initials: D
authors.lastname: Staporn
authors.forename: Takahisa
authors.initials: T
authors.lastname: Maeda
authors.forename: Minoru
authors.initials: M
authors.lastname: Gamo
authors.forename: Sapit
authors.initials: S
authors.lastname: Diloksumpun
authors.forename: Ladawan
authors.initials: L
authors.lastname: Puangchit
authors.forename: Moriyoshi
authors.initials: M
authors.lastname: Ishizuka
mesh_terms: D002980:Climate; D018515:Plant Leaves / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology*; D012621:Seasons; D013785:Thailand; D013997:Time Factors; D014197:Trees / Q000502:physiology*; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water