Damage Analysis Of Dust Pollution On The Leaves Of Four Types Of Fruit Tree In Sothern Xinjiang

Plants depend on their leaves to both protect themselves from and reduce the damage caused by dust in the atmosphere.If an excessive amount of dust particles,gather on the surface of the leaf,it can exert a negative effect on the normal growth of the entire organism.In this paper,taking the leaves of the walnut,apricot,paddan and apple trees as objects of research,making investigations into their ability to retain dust at a variety of times and heights.After artificially simulating both dust-coverings（thin:3 mg/cm²,thick:8.8 mg/cm²）and shade（light:16.4%,severe:46.5%）,taking measurements over a series of nine day intervals（i.e.nine days,eighteen days,twenty-seven days and thirty-six days）,analysing the effect dust and shade have on enzyme activity,organic osmotic adjustment substances and the levels of chlorophyll fluorescence in the leaves of the four fruit trees mentioned above.in addition to this,this paper also use a scanning electron microscope（SEM）to make observations of the varying degrees of damage caused by dust and shade to the surface of the leaf.The main results showed as follows:（1）With the passage of time,the amount of dust retention held by the four types of leaf showed a significant increase（P<0.01）.Leaves on the same tree had different dust retention abilities,depending on their heights.As their heights increased,their ability to retain dust fell,the order of:1 m>2 m>3 m.（2）After being treated with a light covering of dust,SOD activity were higher than control,and gradually upregulated with the increasing of dust cover time.What’s more,this increase in enzyme activity continued even further with time,reaching a high of 131.46%when compared to the control group at thirty-six days of dust coverage.Activites of POD and CAT increased first and then decreased.After being treated with a heavy covering of dust,levels of SOD,POD and CAT all peaked and then saw a fall after twenty-seven days,eighteen days and nine days,respectively.The tendency of heavy treatment was greater than that of mild treatment.Under light shading,four fruit tree leaves showed an increase in SOD and CAT activity,in correlation to the length of time subjected to shade.This peaked at thirty-six days,reaching a respective high of 108.57%and 52.03%when compared to the experimental control group.POD activity,however,decreased after showing the maximum value on 18th day.Under severe shading,all phsiological indexes of four tree leaves increased first and then decreased.（3）In the dust coverage experiment,the amount of proline and soluble sugar saw a gradual increase when exposed to a light covering of dust.The amount of soluble protein,however,increased to a total of45.83%,compared to the control group,and then fell sharply.When subjected to a heavy dust covering,levels of soluble protein,proline and soluble sugar all peaked between the ninth and eighteenth day and then dropped significantly.After a light shading treatment,the three aforementioned osmoregulation substances increased by differing degrees.In contrast,however,as shading increased,soluble protein and proline both tended to decrease,peaking between day eighteen and twenty-seven.Chlorophyll fluorescence parameters such as ETR,R_fd,qN and qL were suppressed in all of the tested leaves under the dust and shading stress condition.When in severe danger of damage from dust or shade,the figures all of the four species of plant showed a common rising and falling trend.The exact amount,however,differed from species to species.（4）Principal component analysis showed that the order from strong to weak in resistant dust capability are walnut>paddan>apple>apricot.（5）SEM results indicate that,after being exposed to dust or shade,the stratum corneum on the surface of the leaf experienced varying degrees of damage.Leaves which were subject to regular cleaning or kept in a natural condition,however,were subject to less damage.Damage caused by dust to the a leaf’s stratum corneum is significantly higher than the damage caused by shade.