Abstract: To alleviate the stress from heavy metals and reduce their toxic effects on crops, the effects of jasmonic acid (JA), melatonin (MT), spermidine (SPD), and 2,4-epibrassinolide (EBL) on physiological indices, uptake and accumulation of Cd and As in rape under combined Cd and As stress were examined. The results showed that spraying JA and MT at a concentration of 200 μmol·L^-1 significantly increased and spraying 20 μmol·L^-1 EBL significantly reduced the chlorophyll SPAD value of rape leaves. Spraying 500 μmol·L^-1 SPD and 20 μmol·L^-1 EBL significantly reduced the MDA content in rape leaves by 41.0% and 52.3%, respectively, whereas 20 μmol·L^-1EBL treatment significantly increased the SOD activity of rape leaves by 88.2%. Spraying 200 μmol·L^-1 MT significantly decreased Cd concentration in the shoots of rape by27.8% compared with CK treatment, while spraying 200 μmol·L^-1 JA and 20 μmol·L^-1 EBL significantly increased As concentration in the shoots of rape by 159.8% and 136.8%, respectively. Our results suggested that JA, MT, SPD and EBL can alleviate the stress of combined Cd and As pollution on rape, providing remediation materials for controlling heavy metal pollution in croplands.

Key words: North China Plain., farm level, mixed crop-livestock system, nitrogen use efficiency, nitrogen flow characteristic