[Effects of Exogenous Substances on the Remediation of Soil Contaminated by Heavy Metals and Greenhouse Gas Emissions by <i>Pennisetum americanum</i>×<i>Pennisetum purpureum</i> and <i>Helianthus annuus</i>].

The application of exogenous substances has important effects on soil greenhouse gas emissions and phytoremediation of soil contaminated by heavy metals. <i>Pennisetum americanum</i>×<i>Pennisetum purpureum</i> and <i>Helianthus annuus</i> 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 <i>P. americanum</i>×<i>P. purpureum</i> soil but significantly reduced the pH value of <i>H. annuus</i> 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 <i>H. annuus</i>. 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 <i>H. annuus.</i> 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 <i>P. americanum</i>×<i>P. purpureum</i> and <i>H. annuus</i> and the accumulation of Cd in <i>P. americanum</i>×<i>P. purpureum</i> roots, and the application of EDDS significantly increased the accumulation of Pb in <i>H. annuus</i> shoots and <i>H. annuus</i> 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 <i>P. americanum</i>×<i>P. purpureum</i> planting soil and 15.8% and 45.9% in <i>H. annuus</i> 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 <i>P. americanum</i>×<i>P. purpureum</i> soil but decreased the cumulative N₂O emissions of <i>H. annuus</i> soil to different degrees. Compared with those in the CK treatment, the application of KCl and GA₃ significantly reduced the cumulative N₂O emissions of <i>H. annuus</i> 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 <i>H. annuus</i>, and the KCl and EDDS treatments enhanced phytoremediation efficiency and reduced soil greenhouse gas emissions to varying degrees.