| Glycine max.are exposed in the open-top chambers to three levels of ozone(O3) concentration(ambient,approximately 45 nL·L-1 and two elevated ozone,80±10 nL·L-1 and 110±10·nL-1) in order to study the effect of different ozone concentration on photosynthesis, lipid peroxidation,active oxygen metabolism,osmotic adjustment substances,antioxidation defence system and protective enzymes isozymes in Glycine max.leaves.This paper reveals its response process and response degree of defence system and protective enzymes isozymes in soybean under different elevated O3,and it could establish the foundation for the study of plants adaptability mechanism under elevated O3 on the molecular level.The results show:Chlorophyll and Chla content decreases significantly under elevated O3,and the larger the O3 stress intensity is,the shorter Chlorophyll and Chla content are.Besides the individual time O3 concentration for 80±10 nL·L-1 treatment slightly is higher than the control,Chlb content and Chla/b are lower than CK under different elevated O3,but two elevated O3 treatment,does not have the remarkable changes in the whole growing stages.It can be seen that different elevated O3 inhibits chlorophyll content of the soybean leaves.Elevated O3 could reduce Pn,Gs,Tr of soybean leaves significantly.It indicates elevated O3 in soybean leaves to net photosynthetic rate,stomatal conductance and transpiration rate show a negative effect and the higher the O3 concentration is,the more negative effect is obvious.The effect of elevated O3 to Ci in soybean leaves is different,when O3 concentration for 80±10 nL·L-1,Ci is lower than the control in the branching and flowering stage and is higher than CK in the podding and filling stage.When O3 concentration for 110±10 nL·L-1,Ci is lower than CK in the whole growing stage.Elevated O3 reduces carotenoid and ASA content.But SOD activity has short-term increase at branching stage and SOD activity is lower than the control under elevated O3. Except that APX activity of plants increases slightly under O3-1 treatment,elevated O3 decreases significantly or best significantly POD activity,CAT activity and APX activity in soybean leaves.Generally,elevated O3 to protection material and the protection enzyme activity in soybean leaves performs for the injury function and the higher the O3 concentration is,the more injury function is obvious.The effects of elevated O3 on SOD isozyme,POD isozyme,CAT isozyme and APX isozyme have not manifested in the enzyme belt strip number change,but manifests in the enzyme belt width or in brightness change,which causes the original enzymatic system activity change.SOD,POD,CAT activity and theirs isoenzyme activity are basically same, but APX activity and APX isoenzyme activity are different.Compared with the control,the soluble sugar,protein and proline content increase firstly and then decrease in soybean leaves under elevated O3.It shows that elevated O3 to soybean has some resistance,but with the treatment time prolonging,soybean plants are injuried by highly elevated O3 injury.And the extent of this injury and O3 concentration are positively correlated.Elevated O3 increases the yield of soybean significantly.With the increase of O3 concentration,soybean grains number,seed weight,100-seeds weight and number of pods per plant decrease repectively.And the higher the O3 concentration is,the greater the decrease is.Under elevated O3 condition,the yield of soybean plants and the control was remarkable or the extremely remarkable difference.Generally,elevated O3 can decrease photosynthesis and antioxidant capacity,but increase the accumulation of active oxygen,decrease SOD,POD,CAT activity and its isoenzyme activity,which increase peroxidation damage and decrease the accumulation of osmotic adjustment substances,resulting in reduced soybean production.So the higher O3 concentration is,the more the jury effect of O3 stress on soybean protection system is obvious.
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