Abstract: To assess the gas exchange parameters,chlorophyll,accumulation of assimilation products and antioxidation system of winter wheat (Triticum aestivuml Yangmai13) under elevated O3 and reduced solar irradiance,five field experiments were conducted inside open topchambers (OTC).Five treatments (CK,T1,T2,T3and T4) were designed as follows:CK consisted of nature O3 concentration and nature solar irradiance,T1 of 100nL·L-1 O3 concentration and 40% of nature solar irradiance,T2 of 100nL·L-1 O3 concentration and 60% of nature solar irradiance,T3 of 100nL·L-1 O3 concentration and 80% of nature solar irradiance,T4 of 100nL·L-1 and no shading.The results showed that O3 stress caused intercellular CO2 concentration increasing,leaf photosynthetic rate,chlorophyll (chl) and carotenoid (Car) decreasing;O3 and shading composite treatment accelerated the net photosynthetic rate declining,while it could relieve chlorophyll (chl) and carotenoid (Car) falling.The photosynthetic rate descending were caused by nonstomatal factors under the two kinds of circumstances.O3 stress significantly increased leaf soluble sugar and total free amino acids,the soluble protein was significantly reduced;Under O3 and shading composite treatment,leaf soluble sugar no longer increased,and soluble sugar and soluble protein content declined,while the total free amino acid content continues to increase as the shading intensified.Carbon metabolism was planted major supersession under O3 stress,adding the weakened radiation to ozone stress changed the metabolism of plants,the main metabolism converted Carbon into nitrogen metabolism.O3 stress increased leaves malondialdehyde content(MDA),catalase (CAT),peroxidase(POD),superoxide dismutase (SOD) activity;Under O3 and shading composite treatments,leaves MDA decreased significantly,CAT,POD,SOD content was significantly higher,it indicated that increased antioxidant enzymes of plant could not completely eliminate excessive reactive oxygen species,leading to accumulation of reactive oxygen species,which resulted in the increase of membrane permeability under O3 stress,reduced solar irradiance relieved the damage of ozone on plants in a certain extent.

Key words: hading, O3, Net photosynthetic rate, Intercellular CO2 concentration, Soluble protein content, Chlorophyll content