Effects Of Leaf Structure On The Ability Of Fine Particulate Matter Of Tree Species In Urumqi

With the acceleration of urbanization and industrialization,air pollution caused by population growth and motor vehicle exhaust emissions has brought serious harm to the physical and mental health of citizens and the quality of ecological environment.As the main carrier of atmospheric particulates,the green leaves play an irreplaceable role in controlling particulate matter pollution and improving air quality.Urumqi,Xinjiang,is deep in inland arid area.The terrain and climate conditions surrounded by mountains on three sides are not conducive to the diffusion of exhaust gas and particulates in urban areas.Therefore,reasonable selection of urban greening is a scientific issue to be solved to improve the living environment of cities in arid regions.In this research,based on the trend of atmospheric pollution and the situation of main pollutants in Urumqi,17 types of common green trees and shrubs in urban built-up areas were selected.Through field experiments and indoor analysis,the difference of retained particulate matter(PM_>10,PM_3-10,PM_1-3)per unit leaf area of different tree species was discussed.Secondly,by means of scanning electron microscopy（SEM,S3400N）,the effects of leaf traits and leaf microstructures on the retention capacity of plants and their mechanisms were further explored and analyzed in order to provide scientific basis for the selection of urban greening tree species in arid areas.The results are as follows:1)From 2014 to 2017,the concentrations of PM_2.5、PM₁₀、SO₂、NO₂、CO and other atmospheric pollutants in Urumqi showed a trend of high in spring and winter,low in autumn and summer,and high in spring and summer,and low in autumn and winter.Daniel trend test Spearman rank correlation coefficient method found that PM_2.5 and PM₁₀0 showed an upward trend year by year which means that particulate matters in the atmosphere is the main pollutant.PM_2.5 is highly correlated with other atmospheric pollutant concentrations,and the correlation coefficient R is greater than0.5,while showing the lower correlation with meteorological factors.2)The amount of particulate matter retained on the leaves of 17 common road greening plants in Urumqi was determined by gravimetric method.The order of particulate matter was:Begonia evansiana>Ulmus densa Litw>Crataegus pinnatifida Bunge>Flos caryophyllata>Armeniaca vulgaris Lam.>Catalpa speciose Engelm>Lonicera japonica Thunb.>FraxinuschinensisRoxb.>Salixbabylonica>Elaeagnus angustifolia Linn.>Amygdalus davidiana de Vos ex Henry>Rhus Typhina>Populus tomentosa Carr>Euonymus maackii Rupr.>Quercus robur L.>Acer L.>Swida alba Opiz.There are also differences in the retention of particulate matter with different particle sizes among tree species,especially Yushu and Rendong.Catalpa speciose Engelm（3.55+0.25ug/cm²）and Salix babylonica（2.20+0.31 ug/cm²）retained more PM_3-10 coarse particles,while Elaeagnus angustifolia Linn.（1.08+0.05 ug/cm²）and Euonymus maackii Rupr.（1.04+0.06 ug/cm²）retained more PM_1-3 fine particles.3)Through the analysis of particle size composition on the leaf surface,we found that the retention of different particle sizes on the leaf surface of the tested tree species was significantly different.Dust fall(PM_>10)was the main particulate matter retained on the leaf surface.The retention of shrubs and trees was slightly larger than that of small trees,followed by PM_3-10 and PM_1-3.At different distances from the source of pollution（Hetan expressway）,there were significant differences in the amount of total particulate matter retained in the leaves of the same tree species,which were as follows:10m height>25m height>40m height.4)There were significant differences in leaf traits（leaf thickness,aspect ratio,petiole aspect ratio,specific leaf area and total water content）among different tree species.Among them,the ratio of petiole diameter to length was positively correlated with PM_3-10 and PM_1-3,but weakly with PM_>10and TSP.In addition,the order of the effects of leaf trait parameters on particulate matter retention was SLA>leaf thickness>aspect ratio>TWC.SLA was negatively correlated with the aspect ratio,and leaf thickness was positively correlated with the retention of dust(PM_>10,TSP)and negatively correlated with the retention of particulate matter of PM_3-10and PM_1-3.5)Leaf surface microstructures have a certain effect on the ability of particulate matter retention in leaves.The stomatal length,stomatal short diameter and stomatal area were positively correlated with PM_>10 and TSP per unit area of leaves,among which stomatal length was most remarkable;stomatal number and stomatal density were positively correlated with PM_1-3 retention of leaves.The regression model of villus length and particulate matter retention in leaves showed that villus length had a good polynomial relationship with PM_3-10 and PM_1-3,indicating that the effect of fine particulate matter retention in leaves was more obvious.The width of groove was negatively correlated with PM_>10 and TSP retention.The larger the width of groove,the more difficult it was for particulate matter to remain on the surface of leaves.