Abstract:

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.