| Lagerstroemia indica belonging to lythraceae Lagerstroemia and is a deciduous shrubs or small trees,with a variety of varieties and a wide range of garden uses.Among them,the new leaves in spring are bright red,and the leaves in autumn often have different degrees of purple,red,orange,yellow and other changes in addition to the normal leaf color,adding a lot of elements to the garden color in spring and autumn.In order to find out the reasons for the seasonal change of leaf color,this study took the common L.indica varieties in Zhengzhou as the research object.L.indica has two periods from germination in spring to stable leaf color and from chlorosis in autumn to before deciduous,(calling these two periods as color changing period),firstly,the change law of leaf color morphology and physiological indexes in these two periods was studied.Through the research on the dynamic changes of leaf color,color parameters,pigment content and other indicators of leaves during the color-changing period,the coloring mechanism of L.indica leaves during the color-changing period was preliminarily discussed;Secondly,three types of L.indica,such as Lagerstroemia speciosa and ’Fast-growing’ L.indica with no obvious color transformation period,L.indica varieties with obvious color transformation period ’Dynamite’ and’Whit lll’,and annual violet-leaf variety ’Ebony Embers’,were subjected to specific illumination and light treatment and drought treatment,The effects of light and drought on the color change period and leaf color of L.indica were discussed,especially the changing laws of physiological indexes such as pigment content,enzyme activity and soluble sugar content under drought stress.The main research results were as follows:(1)The new leaves on the very short young branches in the early stage of color change in spring were purple or red,and gradually turned green.The whole process lasted for 2-3 weeks,and the chlorophyll content of the leaves increased;the anthocyanin content decreased significantly;the carotenoid content basically Stable,slightly increased,the overall maintained at 0.25-0.45mg/g;The differences of different leaf positions and different varieties affected the leaf pigment content and its fluctuation trend of L.indica.The variation trend of anthocyanins in different leaf positions on the same branchlet was somewhat different,and the anthocyanin content of upper leaves was higher than that of lower leaves.(2)The leaf color changes of crape myrtle during the veraison period in autumn were more abundant and diverse than those in spring,and the maintenance time of the veraison period was also extended,which was 4-5 weeks.The leaves of ’Fenjiao Rong’and ’Chuizhi Fen’ appear yellow in the early stage because their carotenoids are decomposed slower than chlorophyll,and the relative content of carotenoids in leaves is lower.The content of anthocyanins in the leaves of ’Caixia Mantian’ and ’Red Rocket’ was accumulated faster,which also caused the difference in leaf color among the crape myrtle varieties to a certain extent;the red leaves of the four crape myrtle varieties in autumn were mainly caused by the large increase in the content of anthocyanins.The difference in pigment content and trend will have a certain impact on the expression of crape myrtle leaf color.The autumn leaf color changes of the four crape myrtle varieties are mainly two types,one is green-yellow-orange-red,and the other is green-purple.(3)During the color transition period of spring and autumn,red-green phase(a*),yellow-blue phase(b*),chromatic value(s),color angle(h),color ratio(H),brightness(L*)and The changing law of the 7 types of leaf color parameters such as saturation(C)is as follows: a*,s and H of leaves at the initial stage of color change in spring are positive values,and gradually decrease to negative values with the color change period,and the color angle h is 30°-50°,rising rapidly to 110°-125° in the middle and late stages,which corresponds to the phenomenon that the new leaves of L.indica gradually turn green;L*,C first increased and then decreased,and b* decreased first and then increased;in autumn The a*,s,and H values of the leaves of L.indica in the early stage of color transformation are negative,and rise to positive values with the time of color transformation,corresponding to the phenomenon of autumn leaves turning red,the overall trend is completely opposite to that in spring.Correlation analysis showed that:the content of anthocyanins in crape myrtle leaves was significantly correlated with the color parameters a*,H,h,s;it indicated that the fading of new leaves of crape myrtle in spring and the redness of autumn leaves were closely related to the content of anthocyanins.The Lab model to a certain extent,it can reflect the expression of leaf color during the color change period of L.indica in spring and autumn.(4)5000lx light treatment will affect the phenotype of L.indica leaf color and the growth rate of leaves,and the synthesis and degradation rate of pigments will be slow,which will reduce the accumulation of pigments and anthocyanins in leaves.Unfavorable;different light intensities have different effects on the expression of leaf color during the color transformation period of crape myrtle.In the early stage of15000 lx treatment,the leaf color of ’Dynamite’ and ’Whit lll’ was bright red,and the leaf color mostly changed from red to green,and the duration of red color was also longer;5000lx At the beginning of the treatment,except ’Ebony Embers’ and ’Whit lll’,the leaf color of the rest of the new leaves were mostly light yellow and light green,and finally turned to light green;even under the same light,the accumulation of anthocyanins in each cultivar at the beginning of the color change was also different.Different,will lead to different expression of leaf color,which is caused by the differences of varieties.The decrease of light had relatively little effect on the leaf color of ’Ebony Embers’ and ’Whit lll’.(5)Mild drought stress can increase the contents of anthocyanin and soluble sugar and POD enzyme activity in leaves,but severe stress has greater damage to crape myrtle,and has a greater impact on the shape and color of crape myrtle leaves: during drought stress,the chlorophyll content of leaves of all cultivars showed a significant downward trend;some leaves turned yellow and chlorotic,and the yellow color increased until the leaves died;the edges of other leaves became black,and the leaves gradually curled and shrank until the whole leaves withered.Through correlation analysis,it can be speculated that soluble sugar is involved in the synthesis of anthocyanin,and PPO enzyme is involved in the degradation of chlorophyll,but POD has no effect on the change of crape myrtle leaf color.After drought stress,the PPO activity of leaves of all cultivars decreased.Among them,the PPO activities of leaves of ’Dynamite’ and ’Whit lll’ decreased significantly,by 80% and 90.7%,respectively,and the changes of POD activity of leaves of ’Ebony Embers’ were smaller.In the early stage of drought stress,the Fv/Fm of the five cultivars of L.indica showed a very slow decline,and the decline speed was accelerated in the later stage,and the decline of’Fast-growing’ was the largest.(6)During drought stress,the leaf color parameters of cultivar ’Ebony Embers’ and the other 4 cultivars were quite different.The changing trend of leaf color parameters of ’Dynamite’ and ’Whit lll’ was basically consistent.The changing trends of the parameters are relatively similar.Correlation analysis showed that there was no significant correlation between the same pigment content and leaf color parameters among cultivars,and the leaf color discoloration types of different cultivars were quite different.The leaf color performance of crape myrtle under drought stress may not be accurately described by the Lab model. |
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