Study On The Leaf Of Chromogenic Mechanism Of Acer Negundo ’Aurea’

Acer negundo‘Aurea’leaves are golden and graceful,widely used in landscaping,but the phenomenon of re-greening the plants made the ornamental effect weaker.This paper studied the leaf color parameters（L*,a*,b*）,physiological indexes,photosynthetic characteristics and leaf microstructure of Acer negundo‘Aurea’and Acer negundo in different time and space.Preliminary discussion of the coloring mechanism of Acer negundo‘Aurea’,providing a theoretical basis for the study of leaf color changes and mechanisms of golden leaf plants in the north,and the main findings were as follows:（1）The L*and b*values of leaf color parameters of Acer negundo‘Aurea’were significantly higher than those of Acer negundo.The a*value showed significant difference only in May.Except for the ratio of carotenoid/total chlorophyll,the physiological indicators were all lower than Acer negundo.The annual changes in the leaves of Acer negundo‘Aurea’were as follows:golden yellow-yellow green-bright green-dark green-green.Leaf color parameters fluctuate from falling first and then rising over time,the chlorophyll content of the inner layer of leaves presented a single-peak curve that first rose and then fell,and the outer leaves presented a double-peak curve of rising-falling-rising-falling,with the highest variation range up to 845.00%;Anthocyanin,carotenoid content and cell fluid p H continued to rise;carotenoid/total chlorophyll ratio first decreased and then increased;Soluble sugar content showed a seasonal change of up-down-up.The change in leaf color of Acer negundo‘Aurea’leaf was affected by various physiological indicators.The increased of chlorophyll and anthocyanin content and the decreased of relative carotenoid content directly affected the yellowness of Acer negundo‘Aurea’,the soluble sugar and cell fluid p H indirectly adjusted the leaf color of the Acer negundo‘Aurea’.（2）The leaf color of Acer negundo‘Aurea’was affected by light.The light intensity had a very significant positive correlation with leaf color parameters and the ratio of carotenoid/chlorophyll total.Strong light made the decomposition of chlorophyll up to78.54%and the decomposition of carotenoids up to 46.80%,which was conducive to leaf color;weak light was conducive to photosynthesis.The accumulation of pigments inhibited the appearance of yellow leaves.The leaf color parameters L*,a*,b*values of the azimuth east,azimuth south and canopyⅢwith strong light were significantly or very significantly higher than other positions,while the azimuth west,azimuth north and canopyⅠleaves with poor light Chlorophyll content and carotenoid content were very significantly higher than other locations.（3）The photosynthetic capacity of Acer negundo‘Aurea’was lower than that of Acer negundo;The photosynthetic capacity of the outer leaves of Acer negundo‘Aurea’was higher than that of the inner leaves at all stages,and the net photosynthetic rate of the outer leaves showed an asymmetric bimodal curve,reaching the maximum values of 10.10 umol·m^-2·s^-1and 10.67 umol·m^-2·s^-1in June and August,respectively.The inner leaves continued to increase,reaching a maximum of 7.166 umol·m^-2·s^-1in August;The photosynthetic pigment content was the lowest in the east leaves of Acer negundo‘Aurea’where the light was stronger,but the photosynthetic capacity was the strongest,light had greater influence on photosynthesis than photosynthetic pigments.（4）The thickness of each tissue and the ratio of palisade tissue/sponge tissue of golden leaves in Acer negundo‘Aurea’were significantly lower than that of Acer negundo.The thickness of leaf and the thickness of each tissue increased significantly after re-greening,reaching the similar level with Acer negundo;Leaf color parameters were significantly negatively correlated with leaf thickness,upper epidermis thickness,palisade tissue thickness,the ratio of palisade tissue/sponge tissue,and length and width of chloroplast,but had not reached a significant level with the thickness of upper epidermis and sponge tissue.Compared with Acer negundo and re-green leaves,the golden leaf of Acer negundo‘Aurea’had smaller chloroplast volume,incomplete development and lack of thylakoid stacking.It was the main reason for the low chlorophyll content,poor photosynthetic capacity,thus showed golden of Acer negundo‘Aurea’.