title: Photoprotection of evergreen and drought-deciduous tree leaves to overcome the dry season in monsoonal tropical dry forests in Thailand.
abstract: In tropical dry forests, uppermost-canopy leaves of evergreen trees possess the ability to use water more conservatively compared with drought-deciduous trees, which may result from significant differences in the photoprotective mechanisms between functional types. We examined the seasonal variations in leaf gas exchange, chlorophyll fluorescence and the amounts of photosynthetic pigments within lamina of the uppermost-canopy leaves of three drought-deciduous trees (Vitex peduncularis Wall., Xylia xylocarpa (Roxb.) W. Theob., Shorea siamensis Miq.), a semi-deciduous tree (Irvingia malayana Miq.) and two evergreen trees (Hopea ferrea Lanessan and Syzygium cumini (L.) Skeels) in Thailand. Area-based maximum carbon assimilation rates (Amax) decreased during the dry season, except in S. siamensis. The electron transport rate (ETR) remained unchanged in deciduous trees, but decreased during the dry season in evergreen and semi-deciduous trees. In the principal component analysis, the first axis (Axis 1) accounted for 44.3% of the total variation and distinguished deciduous from evergreen trees. Along Axis 1, evergreen trees were characterized by a high Stern-Volmer non-photochemical quenching coefficient (NPQ), high xanthophyll cycle pigments/chlorophyll and a high de-epoxidation state of the xanthophyll cycle, whereas the deciduous trees were characterized by a high ETR, a high quantum yield of PSII (ΦPSII = (Fm(') -F)/Fm(')) and a high mass-based Amax under high-light conditions. These findings indicate that drought-deciduous trees showing less conservative water use tend to dissipate a large proportion of electron flow through photosynthesis or alternative pathways. In contrast, the evergreens showed more conservative water use, reduced Amax and ETR and enhanced NPQ and xanthophyll cycle pigments/chlorophyll during the dry season, indicating that down-regulated photosynthesis with enhanced thermal dissipation of excess light energy played an important role in photoprotection. Trees with different water uses and leaf lifespans appear to employ different photoprotective mechanisms to overcome the unfavorable dry-season drought. Our data may suggest that future changes in precipitation will strongly impinge on forest structure and functions.
authors: Center for Ecological Research, Kyoto University, 2 Hirano, Otsu, Shiga 520-2113, Japan.
authors: Atsushi
authors: A
authors: Ishida
authors: Jun-Ya
authors: JY
authors: Yamazaki
authors: Hisanori
authors: H
authors: Harayama
authors: Kenichi
authors: K
authors: Yazaki
authors: Phanumard
authors: P
authors: Ladpala
authors: Takashi
authors: T
authors: Nakano
authors: Minaco
authors: M
authors: Adachi
authors: Kenichi
authors: K
authors: Yoshimura
authors: Samreong
authors: S
authors: Panuthai
authors: Duriya
authors: D
authors: Staporn
authors: Takahisa
authors: T
authors: Maeda
authors: Emiko
authors: E
authors: Maruta
authors: Sapit
authors: S
authors: Diloksumpun
authors: Ladawan
authors: L
authors: Puangchit
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D055864:Droughts; D004579:Electron Transport; D008027:Light; D019684:Magnoliopsida / Q000502:physiology* / Q000528:radiation effects; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology / Q000528:radiation effects; D018526:Plant Transpiration / Q000502:physiology; D012621:Seasons; D013785:Thailand; D014197:Trees / Q000502:physiology* / Q000528:radiation effects; D014329:Tropical Climate; D014867:Water / Q000502:physiology; D024341:Xanthophylls / Q000378:metabolism
chemical_list: D024341:Xanthophylls; D014867:Water; D002734:Chlorophyll
keywords: chlorophyll fluorescence; functional type; leaf phenology; photoinhibition