Leaf color characteristics and photosynthetic characteristics of purple-leafed Lagerstroemia indica 'Ebony Ember'

Lagerstroemia indica 'Ebony Embers' with purple leaves was an excellent foliage plant. To compare and analyze the coloration mechanism and photosynthetic characteristics of purple-leafed cultivars of Lagerstroemia indica, L. indica 'Ebony Embers' with purple leaves and L. indica 'Arapaho' with green leaves were used to measure the content of pigments and soluble sugar, pigment distribution and the characteristics of photosynthesis. The results were as followings:1) the contents of chlorophyll, carotenoid and anthocyanin in leaves of 'Ebony Embers' were significantly higher than those in 'Arapaho'. The degree of purple coloration was consistent with the content change of anthocyanin in leaves, indicating that anthocyanin was the crucial pigment for purple coloration in leaves of 'Ebony Embers'. The anthocyanin was mainly distributed in palisade tissue and spongy tissue near the epidermis. 2) The content of soluble sugar in leaves of 'Ebony Ember' was significantly higher than that of 'Arapaho', which showed a positive correlation with the content of anthocyanin in purple leaves. 3) The daily changes of net photosynthetic rate, stomatal conductance, transpiration rate all appeared as single-peak curves in 'Ebony Embers', while those in 'Arapaho' were all double-peak curves. Net photosynthetic rate, stomatal conductance, transpiration rate of 'Ebony Embers' were lower than those of 'Arapaho', indicating that photosynthetic capacity of 'Ebony Embers' was lower than that of 'Arapaho'. However, there was no significant correlation between the decrease in net photosynthetic rate of purple-leaf cultivar and the difference of chlorophyll content. The light compensation point of 'Arapaho' was significantly higher than that of 'Ebony Embers', suggesting that 'Arapaho' has higher ability to adapt to high light. 4) There were no differences between 'Ebony Embers' and 'Arapaho' in F_v/F_m. Both Φ_PSII and ETR of 'Ebony Embers' were significantly lower than those of 'Arapaho', NPQ and qN were significantly higher than those of 'Arapaho', indicating that the electron transfer activity of PSⅡ in 'Arapaho' was higher than that in 'Ebony Embers', while the heat dissipation efficiency of 'Ebony Embers' was higher than that of 'Arapaho', which had higher light protection capability. The results provide theoretical basis for developing new purple-leafed crape myrtle cultivars and garden application of L. indica.