Tree Physiology Advance Access originally published online on December 5, 2008
Tree Physiology 2009 29(2):217-228; doi:10.1093/treephys/tpn018
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Sustained diurnal photosynthetic depression in uppermost-canopy leaves of four dipterocarp species in the rainy and dry seasons: does photorespiration play a role in photoprotection?
1 Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China
2 Corresponding author (caokf{at}xtbg.ac.cn)
3 Graduate University of Chinese Academy of Sciences, 19A Yuquan Road, Beijing 100049, China
4 Weed Science Center, Utsunomiya University, 350 Mine-machi, Utsunomiya 321-8505, Japan
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Abstract |
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Diurnal and seasonal changes in gas exchange and chlorophyll fluorescence of the uppermost-canopy leaves of four evergreen dipterocarp species were measured on clear days. The trees, that were growing in a plantation stand in southern Yunnan, China, had canopy heights ranging from 17 to 22 m. In the rainy season, Dipterocarpus retusus Bl. had higher photosynthetic capacity (Amax) than Hopea hainanensis Merr. et Chun, Parashorea chinensis Wang Hsie and Vatica xishuangbannaensis G.D. Tao et J.H. Zhang (17.7 versus 13.9, 11.8 and 7.7 µmol m–2 s–1, respectively). In the dry season, Amax in all species decreased by 52–64%, apparent quantum yield and dark respiration rate decreased in three species, and light saturation point decreased in two species. During the diurnal courses, all species exhibited sustained photosynthetic depression from midmorning onward in both seasons. The trees were able to regulate light energy allocation dynamically between photochemistry and heat dissipation during the day, with reduced actual photochemistry and increased heat dissipation in the dry season. Photorespiration played an important role in photoprotection in all species in both seasons, as indicated by a continuous increase in photorespiration rate in the morning toward midday and a high proportion of electron flow (about 30–65% of total electron flow) allocated to oxygenation for most of the day. None of the species suffered irreversible photoinhibition, even in the dry season. The sustained photosynthetic depression in the uppermost-canopy leaves of these species could be a protective response to prevent excessive water loss and consequent catastrophic leaf hydraulic dysfunction.
Keywords: chlorophyll fluorescence, electron flow, gas exchange, heat dissipation, hydraulic conductivity
Received June 14, 2008; Accepted September 11, 2008