Leaf structural reddening in smoke tree and its significance

The smoke tree (Cotinus coggygria Scop.) is not only an important ornamental tree that changes the color of its leaves in autumn but also maintains red juvenile leaves on vigorous sprouting shoots. To elucidate the process of leaf reddening in the smoke tree, we examined the structure and function of its leaf venation system, anthocyanin levels, leaf water conservation ability in red juvenile leaves and green mature leaves, leaf temperature, stomata conductance and snap strength of petiole. A combination of thermography, image analyses and photosynthetic measuring technology was used to study the facts of leaf reddening of smoke tree. We found that spatial and temporal heterogeneity in the pattern of leaf reddening in the smoke tree illustrates the interaction between internal metabolism and environmental factors. These results indicate that there are periods that show water and energy imbalances at leaf lamina and that this phenomenon is essential to leaf reddening, especially during periods of leaf expanding and leaf shedding. We consistently observed a relationship between high temperatures and leaf reddening, which indicates the latter is a photoprotective response induced by imbalances in water and energy.