| Korla Fragrant Pear （Pyrus bretschneideri Pehd） is the main cash crops in Korla City of Xinjiang,the pear income has already become an local important source of income. Due to the impacts of climatechange, as well as the special geographical location in Korla City, the dust weather frequently occurs inKorla City, this increase in severe weather has brought great impact on the pear safe production, resultingin leaf photosynthetic rate decreased and light absorption weakened, effecting the absorption, metabolismand growth of pear nutrition elements, and causing a loss flowers during flowering time and young fruitduring fruit setting. Ultimately the dust weather has a great impact on the yield and quality of the pear.In this paper, the Korla Pear tree leaves were used as experimental material, experimental methods ofartificial dust coverage was used to design the dust coverage thickness experiment2,6,9,14,18mg.cm-2（short t-2ime dust stress）, two factors orthogonal test of coverage thickness2mg·cm-2（light stress） and9mg·cm（heavy stress） and coverage time7d,14d,28d and42d （long time dust stress）. Making the nonedust coverage as the reference, this paper analyzed micro-meteorological condition, photosynthesis, andphotoinhibition of leaf optical system II （PSII） under different dust cover thickness, and leavesphotosynthesis, photoinhibition of leaf optical system II （PSII）, chlorophyll content and antioxidant enzymeactivity etc photosynthetic and physiological indicators under different dust coverage time. The mainconclusion as following:1. Dust experiments under different cover thickness showed that: dust significantly effects the leaves’solar radiation, net photosynthetic rate （Pn）, transpiration rate （Tr）, stomatal conductance （Gs）, leaf surfacetemperature （TL）, the initial fluorescence （Fo）, PSII maximum photochemical efficiency （Fv/Fm）. Withthe increase of different dust cover thickness, when dust quantity is up to18mg·cm-2, stomatalconductance dropped82%than control group, seriously blocking the stomata, leading to a55%drop of netphotosynthetic rate than control group, making the leaves’ surface temperature rise by3oC at the largestamount of dust than the control group; as well as effected the photochemical reaction PSIIcenters,hampered the process of electron transfer, so that made photosynthetic rate lower.2．Dust experiments under different cover time showed that: dust covering on the leaves surface for along time would cause a certain influence to the energy absorption, resulting in breaking chlorophyllsynthesis balance.-U2nder the same time the dust cover conditions, for the comparison between dustcovering2mg·cmand9mg·cm-2, the amount of dust covering for9mg·cm-2significantly effectednet photosynthetic rate （Pn）, transpiration rate （Tr）, stomatal conductance （Gs）, leaf surface temperature（TL）, initial fluorescence （Fo）, PSII maximum photochemical efficiency （Fv/Fm）, intercellular CO2concentration （Ci）. When Dust amount of9covered for42days, stomatal conductance were down88%compared with control group, leading to a78%drop in net photosynthetic rate than control group; Whilethe longer dust covering time, the greater the effect on photosynthetic parameters. With the extension of thedust cover time, leaf tissue and photochemical reaction center PSII were badly damaged, the electrontransfer process was blocked, and mesophyll cell photosynthetic capacity was lower.Leaves under condition of long time dust coverage, can maintain metabolic balance, protect the leafphotosynthetic structures, protect intracellular reactive macromolecules, slow down peroxidation damagecuased by overlong dust coverage time and by increasing the content of chlorophyll （Chl）, transpiration rate（Tr）, and regulating the activities of antioxidant enzymes; under two different treatment, the leavesenhanced the resistance to the dust by. increasing the content of chlorophyll （Chl）, superoxide dismutase（SOD） and catalase （CAT） activity. |
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