于雾凉季测定了叶片叶绿素荧光参数，探讨了4～6 ℃夜间低温对4种相对光强下生长的两种西双版纳沟谷雨林树苗光系统Ⅱ（PSⅡ）活性的影响及雾对植物的可能保护机制。随夜间低温处理时间延长，不同光强下生长的团花树（Anthocephalus chinensis）和玉蕊（Barringtonia macrostachya）叶片日间和长期光抑制，以及PSⅡ反应中心的可逆失活或破坏加剧，生长环境光越强夜间低温的效应越明显，弱光下其效应不显著。间接表明雾使光强减弱利于缓解自然夜温降低对本区热带植物的影响。中光强下玉蕊对照植株发生了胁迫诱导的光抑制；相同处理条件下玉蕊的光抑制程度均比团花树重，表明玉蕊对夜间低温引起的光抑制更敏感。夜间低温处理后，中等和低光强下团花树的热耗散多于玉蕊，表明其光保护作用较强。夜间低温处理期间两种植物的光抑制与热耗散增多和PSⅡ反应中心的可逆失活或破坏的加剧有关。
We tested the hypothesis that fog can ameliorate the harmful effects of natural nocturnal chilling temperature on tropical plants in Xishuangbanna, Yunnan, China by decreasing growth light intensity in the morning during the foggy and cool seasons. The effects of nocturnal chilling temperature (4-6 ℃) on the chlorophyll a fluorescence was explored in seedlings of two tropical ravine rainforest tree species, Anthocephalus chinensis and Barringtonia macrostachya. A. chinensis is a fast growing, pioneer tree species in the ravine rainforest and B. macrostachya is an intermediate canopy layer tree species and its seedlings distribute in the understory. Seedlings of the two species were grown under four different light intensities (8%, 25%, 50% and 100% full sunlight), and diurnal, stress-induced photoinhibition, and reversible inactivation and/or damage of PSⅡ reaction centers measured. Our results demonstrated that the effects of nocturnal chilling temperature on photoinhibition were significantly intensified under stronger growth light intensities, but its effects were very small under weak growth light intensity (8% sunlight). Fog can decrease light intensity by 60%-90% in the morning during the foggy and cool season; hence, the results presented above indicate that fog can ameliorate the harmful effect of natural nocturnal chilling temperature on Xishuangbanna tropical plants through decreasing growth light intensity. Under intermediate growth light intensity (50% sunlight), stress-induced photoinhibition occurred in untreated B. macrostachya seedlings but not in A. chinensis; furthermore, under the same treatment conditions, the extent of photoinhibition was stronger in B. macrostachya than in A. chinensis. These results suggest that B. macrostachya is more sensitive to temperature-induced photoinhibition. At intermediate and low growth light intensities (25% sunlight), thermal dissipation was greater in A. chinensis than in B. macrostachya after nocturnal chilling temperature treatment, suggesting that protection against photodamage is stronger in A. chinensis. During the period of nocturnal chilling temperature treatment, photoinhibition in the two species was associated with an increase of thermal dissipation and the aggravation of reversible inactivation and/or damage to the PSⅡ reaction center.