The Impact Of Defoliation On Eco-physiological Characteristics And Interrelationship Of Robinia Pseudoacacia L.and Quercus Acutissima Carr.

Since the industrial revolution,the economic development in the world has developed rapidly,the activities of human beings are increasing,the influence and destruction of the nature are increasing,which bring serious interference and influence to the global ecosystem,and bring serious challenges and threats to the survival,development and progress of human society.Global climate change and human activities are important factors affecting plant growth and vegetation dynamics.In natural environment,trees are usually affected by the combined effects of biological stress factors and abiotic(environmental)stress factors.However,there are few studies on the interaction between them,especially on the response mechanism of individual level.Defoliation is a common anthropogenic disturbance of secondary seedlings of warm temperate trees and shrubs.For the purpose of production and life application,the seedlings in the field are often affected by artificial defoliation.Explaining the intraspecific and interspecific relationships of plant seedlings can help transform and restore the zonal vegetation,effectively shorten the succession process,and promote the development of forest stand to a healthy and stable zonal top class community.The combination of defoliation and competition is to cooperate with nature gnawing,human interference and interspecific and intraspecific relationship,help to remould and restore the zonal vegetation,effectively shorten the succession process,and provide scientific data and theoretical basis for guiding the restoration and reconstruction of vegetation and making the sustainable development of regional ecological environment.In this experiment,the annual seedlings of Robinia pseudoacacia L.and Quercus acutissima Carr.,common in Shandong Province,were selected to determine the morphological characteristics,photosynthetic physiological characteristics,biomass accumulation and distribution and other bioecological indexes by setting different degrees of defoliation and species competition cross treatment experiments,and to explore the physiological and ecological effects of defoliation and the interaction between the two species.In this experiment,3 defoliation and 3 planting methods were set up to explore the morphological characteristics,photosynthetic characteristics,biomass accumulation,distribution and relative competitive index of the annual R.pseudoacacia L.and Q.acutissima Carr.seedlings under different defoliation degrees.The results are as follows:Defoliation 25%makes the R.pseudoacacia L.grow better,indicating that moderate defoliation stimulates the longitudinal and lateral growth of R.pseudoacacia L..It can be more easily and stronger to capture the sun,more competitive in the light,and more intense photosynthesis,and can form positive feedback to make the R.pseudoacacia L.grow better.The base stem of defoliation 75%was the smallest,but the crown area was larger than the control group,which indicated that excessive defoliation could cause R.pseudoacacia L.lateral growth slowing,but also could stimulate the growth of crown area,expand its leaves to capture more sunlight for photosynthesis,so as to supplement the loss caused by excessive defoliation,in order to restore to or close to the level of the control group.Q.acutissima Carr.is a slow-growing species with large and few leaves at the seedling stage.Therefore,for the species of Q.acutissima Carr.,which has a relatively slow growth and a weaker recovery ability,the defoliation is the damage and threat to it,and it will not stimulate the growth and development of the Q.acutissima Carr..It can only maintain its survival under the coercive environment,and may be able to recover or close to the original level if it is given enough time to recover and suitable growth conditions.Defoliation resulted in increased total biomass of R.pseudoacacia L.grown separately,and the intensity of defoliation 25%makes this increase significantly.As for the distribution of biomass in each part,defoliation reduced the biomass of R..a pseudoacacia L.to the root,the stem increased,and the leaves changed little;and the intensity of defoliation 25%also made the change more obvious.This indicates that defoliation causes R.pseudoacacia L.to be stressed,in order to ensure their survival and subsequent development,R.pseudoacacia L.will sacrifice the accumulation of biomass and even transfer the biomass of root to the stem and leaf,thereby stimulating the growth of stems and leaves,in order to better use of conditions such as lighting and more vigorous photosynthesis to make up for the loss caused by the defoliation.Defoliation would lead to a decrease in total biomass of Q.acutissima Carr.,and the decrease of total biomass increased with the increase of defoliation intensity.As for the proportion of the biomass of each component in each group,the proportion of the biomass of the control group and the defoliation group did not change much,and the defoliation had a great stress on the Q.acutissima Carr..The intraspecific relative competitive index of R.pseudoacacia L.is positive,and the absolute value is larger,which suggests the total biomass of alone planting were higher than the same planting,namely the performance of R.pseudoacacia L.in the single species is superior to the intraspecific competition.And the interspecific relative competitive index of R.pseudoacacia L.is negative,and the absolute value is smaller,which indicates that the total biomass of the mixed planting is higher than that of the R.pseudoacacia L.planted in the same species,that is,the performance of R.pseudoacacia L.in interspecific competition is better than that of intraspecific competition.The intraspecific relative competitive index of Q.acutissima Carr.is positive,and the absolute value is smaller,which shows the total biomass of alone planting were higher than the same planting,but the difference is not significant,that is,there is little difference of performance between interspecific competition and intraspecific competition of Q.acutissima Carr..The interspecific relative competition index of Q.acutissima Carr.is negative,and the absolute value is relatively smaller,which indicates that the total biomass of the mixed planting is higher than that of the Q.acutissima Carr.planted in the same species,namely Q.acutissima Carr.in interspecific competition's performance is better than that of intraspecific competition.