Keywords :
Thailand Forests; Shorea; Xylia; Dalbergia; Woody Legumes; Dipterocarpaceae
บทคัดย่อ :
Deciduous dipterocarp forests across mainland Southeast Asia are dominated by two
families: the Dipterocarpaceae and Fabaceae. Monsoon conditions produce strong seasonal climates
with a hot dry season of 5-7 months extending from late November or early December through
April or early May. Seasonal measurements of stomatal conductance and plant water potential
found important differences between members of the two families. Despite their long dry season,
Shorea siamensis and S. obtusa (Dipterocarpaceae) showed little significant patterns of seasonal change
in xylem water potentials, with midday potentials never dropping below -1.3 MPa. These species
present a classic example of isohydric strategies of adaptation where stomatal regulation maintains a
relatively stable minimum water potential over the course of the year. However, maximum rates of
stomatal conductance dropped sharply in the late dry season as the leaves heated in full sun without
significant transpirational cooling, reaching as high as 44-45 degrees Celsius, making them potentially sensitive to
global increases in extreme temperature. The woody legumes Xylia kerrii and Dalbergia oliveri present
different patterns of seasonal water relations and leaf response to high temperatures. The legumes
exhibit anisohydric behavior where water potential decreases over the dry season as evaporative
demand increases. Dry season midday water potentials dropped from high wet season levels to -2.4
to -3.2 MPa, moderately lowering maximum stomatal conductance. The relatively small leaflets
of these legumes responded to the high temperatures of the late dry season by temporarily wilting,
reducing their exposure to solar radiation and taking advantage of convective cooling. Large leaf
size of dipterocarps in this community may not be an adaptive trait but rather an ancestral condition
compensated for with ecophysiological adaptations.
เอกสารอ้างอิง :
Rundel, P. W., Boonpragob, K., & Patterson, M. (2017). Seasonal water relations and leaf temperature in a deciduous dipterocarp forest in Northeastern Thailand. Forests, 8(10), 368.
