Keywords :
cryo-SEM, drought, embolism, leaf abscission,
phenology, water relations
บทคัดย่อ :
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 Ktwig), lamina hydraulic conductance
(Klamina) and leaf osmotic potential at full turgor (Yo)
among species, whereas evergreen Syzygium exhibited the
highest leaf-area-specific Ktwig, Klamina and Yo. Deciduous
Xylia had the highest sapwood-area-specific Ktwig, along
with the lowest Huber value (sapwood area/leaf area). More
negative osmotic Yo and leaf osmotic adjustment during the
dry season were found in deciduous Vitex and evergreen
Hopea, accompanied by low sapwood-area-specific Ktwig.
Regarding seasonal changes in hydraulics, no remarkable decrease
in Klamina and Ktwig 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.
เอกสารอ้างอิง :
Ishida, A., Harayama, H., Yazaki, K., Ladpala, P., Sasrisang, A., Kaewpakasit, K., ... & Ishizuka, M. (2010). Seasonal variations of gas exchange and water relations in deciduous and evergreen trees in monsoonal dry forests of Thailand. Tree Physiology, 30(8), 935-945.
