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Changes in photosynthesis, xanthophyll cycle, and sugar accumulation in two North Australia tropical species differing in leaf angles

Xu, S.-M., Liu, L.-X., Woo, K.C., Wang, D.-L.
Photosynthetica 2007 v.45 no.3 pp. 348-354
Acacia crassicarpa, Eucalyptus pellita, absorption, dry season, energy, fructose, glucose, leaf angle, leaves, light intensity, lutein, photoinhibition, pinitol, sucrose, temperature, trees, water stress, Australia
Two tropical species of North Australia, Acacia crassicarpa and Eucalyptus pellita, have similar leaf size and leaf structure but different leaf angles. A. crassicarpa with near vertical leaf angle directly reduced photon absorption and leaf temperature (T ₗ) and had relatively high photosynthetic activity (P ₘₐₓ) and low xanthophyll cycle activity. In contrast, E. pellita with a small leaf angle exhibited high T ₗ, low P ₘₐₓ, and high activity of xanthophyll cycle which was useful for the dissipation of excessive energy and reduction of photoinhibition. In the dry season, contents of soluble sugars including pinitol, sucrose, fructose, and glucose in A. crassicarpa increased whereas larger amounts of only fructose and glucose were accumulated in E. pellita. Different sugar accumulation may be involved in osmotic adjustment of leaves during water stress that makes photosynthesis more efficient. The leaf angle may be critical for developing different protective mechanisms in these two tropical tree species that ensure optimal growth in the high irradiance and drought stress environment in North Australia.