Three wild polygonaceae plants,Polygonum lapathifolium,Polygonum perfoliatum and Polygonum hydropiper,were used to study the physiological responses under five aluminum (AlCl3) concentrations (0,25,50,100,400 μmol/L) with solution culture method.It was found that relative root elongation was decreased with the increase of AlCl3 concentrations in polygonaceae plants,but the magnitude of decrease was higher in Polygonum perfoliatum than that in Polygonum lapathifolium and Polygonum hydropiper,suggesting that Polygonum lapathifolium and Polygonum hydropiper were much more tolerant to Al than Polygonum perfoliatum was.Al contents and oxalate secretion in roots of three polygonaceae plants were increased with increase of AlCl3 concentraions and oxalate secretion showed that a saturating phenomenon at approximately 50 μmol/L AlCl3 in Polygonum hydropiper and Polygonum perfoliatum,while Al contents were significantly lower and the amount of oxalate secretion significantly higher in Polygonum lapathifolium and Polygonum hydropiper than that in Polygonum perfoliatum.When compared with the control,high AlCl3 treatment (400 μmol/L) significantly decreased root activity,leaf activities of peroxides (POD) and catalase (CAT),increased malondialdehyde (MDA) content of three polygonaceae plants,especially in Polygonum perfoliatum.In the low concentration of AlCl3 treatments (25-50 μmol/L),root activity in Polygonum lapathifolium and Polygonum hydropiper showed an increasing trend,and leaf proline content,activities of POD and CAT significantly increased,MDA content significantly decreased compared with the control.These findings suggested that Polygonum lapathifolium and Polygonum hydropiper could enhance the tolerance to Al stress by increasing Al-induced oxalate secretion and maintaining higher proline content,higher activities of POD and CAT,lower MDA content under the low AlCl3 concentration.