PERTANIKA JOURNAL OF SOCIAL SCIENCES AND HUMANITIES

Heat and high light intensity affected physiology and morphology of young Dipterocarpus alatus Roxb. leaf studied. D. alatus is a native forest tree and being extended to cultivation in the field as an economic crop. Nowadays, climate change due to increasing in temperature and light intensity can affect growth, morphological and photosynthetic traits in D. alatus. This research aimed to study the effects of high temperature and strong light intensity on physiology and morphology of the young D. alatus. The experiment was decided in CRD with 5 replications. The two-year-old D. alatus was treated with combination stress between temperature (at 35°C or 41°C) and light intensity (at 700 or 1800 µmol m^-2s^-1) for 7 days. Plant morphology, gas exchange, PSII efficiency and photosynthetic pigment contents were measured. Strong light intensity (1800 µmol m^-2s^-1) affected plant morphology by leaf burning and heat injury. However, high temperature (41°C) combined with strong irradiation enlarged leaf injury and also increased percentage of heat injury (3.01±0.81%; T41L1800) compared to control (0.07±0.00%; T35L700). In contrast, it reduced percentages of leaf angle (-8.77±2.82%) and leaf area (-1.04±0.38%). In addition, the combination stress influenced reduction of net photosynthetic rate and contents of Chl a+b and Chl a but unaffected Chl b and Car contents. Therefore, combined stress affected young D. alatus by damaging photosynthetic pigments such as Chl a and injured leaf tissue. This resulted in reduction in both of photosynthetic mechanism and D. alatus leaf growth. Thus, young D. alatus leaf (two-year-old) was susceptible to heat combined with excessive light.