Study On Deciduous Characteristics And Defoliants Selection Of Ficus Virens Aiton

Ficus virens Aiton is a large deciduous or semi-deciduous tree of Ficus L.of Moraceae,one of the common garden trees in southern China.Ficus virens Aiton has strong nature,plump tree appearance,extended canopy,and can resist strong wind.Also is conducive to summer shading,easy to transplant,and has strong adaptability.It can be used as street tree,landscape tree and court shade tree.However,most Ficus virens Aiton fall leaves in spring,which will lead to poor lighting in winter,thus aggravating the problem of lack of light;in addition,the time of falling leaves is inconsistent between different trees in the same planting section,which causes great difficulties in the construction of landscape unity and environmental sanitation work.This study intends to investigate the defoliation period of Ficus virens Aiton in Chongqing,explore the impact factors of defoliation period,and then analyze the morphological characteristics and internal physiological and biochemical changes of leaves in the process of annual growth,so as to lay a foundation for regulating the defoliation period of Ficus virens Aiton.Ethephon,thidiazuron and urea,which are commonly used as defoliants with low toxicity and high efficiency,were used in the experiment to develop a defoliant formula which can make Ficus virens Aiton defoliate intensively in winter without affecting the germination and growth of the next spring.At the same time,the morphological characteristics and physiological changes of Ficus virens Aiton after spraying defoliant were monitored.The purpose of those experiments are to solve the problems sunlight deficiency,landscape disunity and environmental sanitation caused by Ficus virens Aiton,and provide reference for the application of defoliant in garden greening plants.The main results are as follows:(1)The defoliation period of Ficus virens Aiton in Chongqing in 2019 is from March to May,especially in the middle and late April.And the impact factors of defoliation period of Ficus virens Aiton are not the transplanting time or environmental conditions.(2)The change process of morphological characteristics of the leaves of Ficus virens Aiton in the annual growth process is as follows: the leaf primordium grows to form leaf axis,and then differentiates into leaf,petiole and stipule until the leaf bud unfolds and the bud scale peels off.Then the leaves continue to grow larger,the leaf shape gradually improves,and the leaf color deepens from light green to dark green until the leaves are fully mature.In the aging period,the leaves and petioles gradually lost water and turned yellow from the leaf tip and leaf edge.When the whole leaves were yellow and the detached layer of petiole was clearly visible,the leaves fell off.(3)In the process of annual growth of Ficus virens Aiton leaves,the total water content has been declining.The content of chlorophyll,superoxide dismutase(SOD),soluble protein(SP)and soluble sugar(SS)in leaves of Ficus virens Aiton increased during the period of vigorous metabolism and then decreased after senescence.The content of relative conductivity and malondialdehyde(MDA)decreased during the early and middle growth period and increased after senescence.The content of proline in leaves of Ficus virens Aiton increased,decreased and then increased.In addition,there is a certain correlation between these indicators.(4)After spraying defoliant,the leaves of Ficus virens Aiton turned black gradually from the tip to the edge,and the irregular brown spots in the middle of the leaves changed from less to more,until the large area was lost green and became yellow.At the same time,the veins and petioles were dehydrated seriously,and the phenomenon of yellow and withering appeared.(5)After spraying defoliant,the cells of Ficus virens Aiton leaves were seriously damaged,the content of chlorophyll decreased significantly,then increased in the middle stage,and finally decreased.The relative electrical conductivity,malondialdehyde content,peroxidase,catalase activity and soluble protein content increased in the early and middle stages,but decreased in the late stage.The activity of superoxide dismutase and the content of proline increased all the time.The content of soluble sugar decreased at first,and increased slowly when the leaves resumed growth.Membership function analysis showed that the best formula of defoliant to Ficus virens Aiton was ethephon 0.4%+ urea 8%,which made the defoliation rate reach 100% firstly.