© 2005 Heron Publishing—Victoria, Canada
Photosynthetic acclimation to light changes in tropical monsoon forest woody species differing in adult stature
Z.-Q. Cai (1, 2), T. Rijkers (3) and F. Bongers (3)
1. Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla 666303, P.R. China / 2. Corresponding author (czq@xtbg.org.cn) / 3. Forest Ecology and Forest Management Group, Centre for Ecosystem Studies, Wageningen University, P.O. Box 47, 6700 AH Wageningen,
The Netherlands / Received July 2, 2004; accepted December 4, 2004; published online June 1, 2005
Summary
We studied morphological and physiological leaf and whole-plant features of seedlings of six late-successional woody species
common in the Xishuangbanna lowland rain forest in southwest China. Study species differed in adult stature and shade tolerance
and included the shrubs Lasianthus attenuatus Jack and Lasianthus hookeri C.B. Clarke ex Hook. f.; the sub-canopy species Barringtonia macrostachya (Jack) Kurz and Linociera insignis C.B. Clarke; the canopy tree Pometia tomentosa (Blume) Teijsm. & Binn.; and the emergent species Shorea chinensis (Wang Hsie) H. Zhu. After 1 year of growth in low light (4.5% full sun), seedlings were transferred to high light (24.5%
full sun) to investigate acclimation responses of existing leaves to forest gap opening and to determine whether seedling
capacity for acclimation is a limiting factor in its natural regeneration. Leaves of the shrub species are shade-adapted,
as indicated by their low photosynthetic capacity, efficiency in using sunflecks, low stomatal density, low Chl a/b ratio
and high spongy/palisade mesophyll ratio. The shrub species utilized sunflecks efficiently because they had a short photosynthetic
induction time and low induction loss. In all species, transfer of seedlings to high light resulted in a substantial initial
reduction in the dark-adapted quantum yield of photosystem II (variable chlorophyll fluorescence/maximum chlorophyll fluorescence;
Fv/Fm) at midday. Predawn Fv/Fm of the taller species did not change greatly, but predawn Fv/Fm of the shrub species decreased significantly without complete recovery within 25 days of transfer to high light, indicating
chronic photoinhibition and damage to the previously shade-adapted leaves. Maximum net photosynthetic rate and dark respiration
of the four taller species increased considerably after transfer to high light, but not in the shrub species. Similar trends
were observed for the number of newly formed leaves and relative height growth rate. We conclude that the shrubs L. hookeri and L. attenuatus have limited potential for developmental and physiological acclimation to high light, which explains their absence from forest
gaps. Compared with the shrub species, the taller tree species, which are more likely to experience high light during their
life span, showed a greater potential for light acclimation. Physiological differences among the four tree species were not
consistent with differences in adult stature.
Keywords:
chlorophyll fluorescence, leaf anatomy, light acclimation, photosynthesis, photosynthetic induction.
