title: Seasonal dynamics in photosynthesis of woody plants at the northern limit of Asian tropics: potential role of fog in maintaining tropical rainforests and agriculture in Southwest China.
abstract: The lowland tropical rainforests in Xishuangbanna, Southwest (SW) China, mark the northern limit of Asian tropics. Fog has been hypothesized to play a role in maintaining rainforests and tropical crop production in this region, but the physiological mechanism has not been studied. The goals of this study were to characterize the seasonal dynamics in photosynthesis and to assess the potential for fog to mitigate chilling-induced photodamage for tropical trees and crops in Xishuangbanna. We measured seasonal dynamics in light-saturated net photosynthetic rate (Aa), stomatal conductance (gs), intercellular CO2 concentration, quantum yield of Photosystem II (Fv/Fm) and maximum P700 changes (Pm; indicates the amount of active PSI complex), as well as chilling resistance and fog (light/shading) effects on low temperature-induced decline in Fv/Fm and Pm for native tree and introduced lower latitude tree or woody shrub species grown in a tropical botanical garden. Despite significant decreases in Aa, gs, Pm and Fv/Fm, most species maintained considerably high Aa during the cool season (2.51-14.6 μmol m(-2) s(-1)). Shaded leaves exposed to seasonal low temperatures had higher Fv/Fm than sun-exposed leaves in the cool season. All species could tolerate 1.4 °C in the dark, whereas a combined treatment of low temperature and high light caused a distinctly faster decline in Pm and Fv/Fm compared with low temperature treatment alone. Because fog persistence avoids or shortens the duration of high light condition in the morning when the temperatures are still low, our results provide support for the hypothesis that fog reduces chilling damage to tropical plants in this region and thus plays a role in maintaining tropical rainforests and agriculture in SW China.
authors.affiliation: Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA Sustainability Science Program, Harvard University, Cambridge, MA 02138, USA yongjiangzhang@oeb.harvard.edu caokf@xtbg.ac.cn.
authors.forename: Yong-Jiang
authors.initials: YJ
authors.lastname: Zhang
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
authors.forename: N Michele
authors.initials: NM
authors.lastname: Holbrook
authors.affiliation: Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, and College of Forestry, Guangxi University, Nanning, Guangxi 530005, China yongjiangzhang@oeb.harvard.edu caokf@xtbg.ac.cn.
authors.forename: Kun-Fang
authors.initials: KF
authors.lastname: Cao
mesh_terms: D000222:Adaptation, Physiological; D000383:Agriculture; D002681:China; D003080:Cold Temperature; D008027:Light; D010788:Photosynthesis / Q000502:physiology*; D065947:Rainforest; D012621:Seasons; D014197:Trees / Q000502:physiology*; D014329:Tropical Climate; D014887:Weather
keywords: Asian tropical rainforest; CO2 assimilation; Xishuangbanna; chilling; photoinhibition