© 2003 Heron Publishing—Victoria, Canada
Influence of leaf angle on photosynthesis and the xanthophyll cycle in the tropical tree species Acacia crassicarpa
Li-Xia Liu (1, 2), Shou-Min Xu (1) and K. C. Woo (3)
1. School of Life Sciences, Northeast Normal University, Changchun 130024, China / 2. Author to whom correspondence should be addressed (liulx062@nenu.edu.cn) / 3. School of Biological Sciences, Northern Territory University, Darwin, NT 0909, Australia / Received April 22, 2003; accepted May 24, 2003; published online November 17, 2003
Summary
We examined the effects of artificially altering leaf angle of the tropical tree species Acacia crassicarpa (A. Cunn. ex Benth., Fabaceae) on light interception, leaf temperature and photosynthesis in the wet and dry seasons of tropical
Australia. Reducing leaf angle from the natural near-vertical angle (90°) to 67.5, 45, 22.5 and 0° greatly increased light
interception and leaf temperature, and decreased photosynthetic activity. Compared with the 90° phyllodes, net photosynthetic
rates in the horizontal phyllodes decreased by 18 and 42% by the second day of leaf angle change in the wet and dry seasons,
respectively. The corresponding values for Day 7 were 46 and 66%. Leaf angle reduction also altered the diurnal pattern of
photosynthesis (from two peaks to one peak) and reduced daily CO2 fixation by 23–50% by Day 2 and by 50–75% by Day 7 in the dry season. In contrast, the xanthophyll cycle pool size in the
phyllodes increased with leaf angle reduction. Thus, there are at least five major advantages to maintaining high leaf angle
orientation in tropical tree species. First, it reduces excessive light interception. Second, it lowers leaf temperature.
Third, it protects the photosynthetic apparatus against photodamage by excessive light. Fourth, it minimizes xanthophyll cycle
activity and reduces the cost for xanthophyll biosynthesis. Finally, it enhances photosynthetic activity and helps to sustain
high plant productivity.
Keywords:
diurnal changes, photoinhibition, xanthophyll pool.
