The application of exogenous substances has important effects on soil greenhouse gas emissions and phytoremediation of soil contaminated by heavy metals. Pennisetum americanum×Pennisetum purpureum and Helianthus annuus were used as remediation plants in this study. The effects of different exogenous substances on phytoremediation and greenhouse gas emissions of heavy metal-contaminated soil were studied. The results showed that the application of exogenous substances had little effect on the pH value of P. americanum×P. purpureum soil but significantly reduced the pH value of H. annuus soil compared with that of the background soil. The application of potassium fertilizer （KCl） increased the biomass of plants, enhanced the activities of superoxide dismutase （SOD） and peroxidase （CAT）, and improved the stress resistance of H. annuus. The application of gibberellin （GA3） and indole butyric acid （IBA） decreased the antioxidant enzyme activity and the content of malondialdehyde （MDA） and alleviated the stress of heavy metals in H. annuus. The KCl and EDDS treatments affected the accumulation of Cd and Pb in plants, respectively. The application of KCl significantly increased the accumulation of Cd in P. americanum×P. purpureum and H. annuus and the accumulation of Cd in P. americanum×P. purpureum roots, and the application of EDDS significantly increased the accumulation of Pb in H. annuus shoots and H. annuus roots. Compared with those in the CK treatment, the application of KCl and EDDS could reduce the cumulative CO2 emissions in soil, which were 20.4% and 5.0% in P. americanum×P. purpureum planting soil and 15.8% and 45.9% in H. annuus planting soil, respectively. However, the application of GA3 and IBA could increase the cumulative CO2 emissions. Exogenous substance treatment increased the cumulative N2O emissions of P. americanum×P. purpureum soil but decreased the cumulative N2O emissions of H. annuus soil to different degrees. Compared with those in the CK treatment, the application of KCl and GA3 significantly reduced the cumulative N2O emissions of H. annuus by 40.5% and 43.5%, respectively. The application of EDDS and IBA reduced the cumulative N2O emissions by 20.1% and 28.4%, respectively. In conclusion, the application of GA3 and IBA alleviated the heavy metal stress of H. annuus, and the KCl and EDDS treatments enhanced phytoremediation efficiency and reduced soil greenhouse gas emissions to varying degrees.
Keywords: greenhouse gases; heavy metal; phytoremediation; regulatory measures; soil.