Seasonal Water Relations and Leaf Temperature in a Deciduous Dipterocarp Forest in Northeastern Thailand

Abstract

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 • C, 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.

Impact of Severe Drought during the Strong 2015/2016 El Nino on the Phenology and Survival of Secondary Dry Dipterocarp Species in Western Thailand

“…ex Miq. is considered as a deciduous species in some previous studies [22,49,50], but it never showed complete deciduousness in this study site. Different letters (a,b,c,d,e) mean significant differences by Tukey's honestly significant difference (HSD) tests at 95% confidence level.…”

“…The carbon uptake during the photosynthetically active period can thus compensate for the absence of carbon assimilation during the leafless period [53,54]. However, the stomatal conductance sharply declines when air temperature becomes higher than 40 • C. This will promote high leaf temperatures and thus reduced photosynthetic efficiency [22].…”

“…Recent studies indicate that some species in this family are sensitive to warm temperature. Leaf temperatures can be higher than 7-8 • C compared to air temperature due to their isohydric strategies leading to less transpirational cooling ability [22].…”

Plant Diversity, Traditional Utilization, and Community-Based Conservation of the Small-Scale Nong Sakae Community Forest in Nakhon Ratchasima, Thailand

“…Recognizing the plant species and their distribution within the forest is crucial for conservation efforts. Our study found that a high number of the Fabaceae family, which is dominated in the deciduous dipterocarp forests across mainland Southeast Asia (Rundel et al, 2017). Furthermore, it is essential to highlight that a bamboo species, V. ciliata A. Camus, is among the plant species discovered in the Nong Sakae Community Forest.…”

No evidence of homeostatic regulation of leaf temperature in Eucalyptus parramattensis trees: integration of CO2 flux and oxygen isotope methodologies

“…This work is consistent with a large body of literature regarding the biophysical controls of leaf temperature. We recognize that many aspects of plant morphology and physiology can influence T leaf relative to T air , including leaf width, foliar clumping, canopy‐scale influences on atmospheric mixing, and latent cooling from transpiration (Jarvis & McNaughton, 1986; Hadley & Smith, 1987; Smith & Carter, 1988; Leuzinger & Körner, 2007; Leigh et al ., 2012; Rundel et al ., 2017; Wright et al ., 2017; Drake et al ., 2018). However, the evidence presented here emphasizes the strong environmental control of T air on T leaf .…”