Abstract: ObjectiveThe influence of heavy metal mercury(Hg)on photosynthesis characteristics and physiologi-cal indexes of Atracty lodeslancea(Thunb.)DC.was investigated and threshold of A.lancea leaves under mercury stress was studied to provide theoretical basis for pollution-free cultivation of A. lancea.MethodMercury stress of different concentrations(0,10,20 and 50 mg/kg)on A.lancea was conducted by pot experiment.The photosynthetic characteris-tics and physiological indexes of A.lancea leaves were determined 0,7,14,21,28 and 35 d after stress.ResultUnder mercury stress of different concentrations,net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs) and intercellular carbon dioxide concentration(Ci)of A.lancea seedlings went through a up-down variation in general as stress time prolonged,at stress late period,photosynthetic capacity of A.lancea dropped greatly.After mercury stress of different concentrations,activity of superoxide dismutase(SOD)in A.lancea leaves did not change greatly,but peroxi-dase(POD)and content of malondialdehyde(MDA)increased first and then decreased in general,and reached the peak on day 28 after stress.Catalase(CAT)activity increased in general(except for stress under 50 mg/kg concentration).After 35 d of mercury stress,A.lancea treated by 10 mg/kg concentration had the highest POD,SOD and CAT activities.MDA content in the leaves went through an up-down change under mercury stress of various concentrations in general,but rela-tive conductivities showed a linear upward trend.ConclusionWhen the mercury stress concentration is higher than 10 mg/kg,photosynthetic capacity of A.lancealeaves would be inhibited,which will damage its physiological functions.