Regulation mechanisms of the combined addition of nitrogen fertilizer and nitrification inhibitor on phytoremediation efficiency and greenhouse gas emissions in heavy metal contaminated soil: A field study

Soil heavy metal pollution and greenhouse gas emission have become global issues. A field study was conducted to explore the effects of using calcium ammonium nitrate (CAN) alone and in combination with 3,4-dimethylpyrazole phosphate (DMPP) on phytoremediation of Cd, Pb, and Zn polluted farmland by Cosmos sulphureus as well as Pennisetum americanum × P. purpureum, and investigate the impact on soil CO2 and N2O emissions during this process. The results show that phytoremediation reduced soil pH and NH4+ -N contents, but increased invertase and urease activities, readily oxidizable carbon, microbial carbon, and NO3--N contents. DMPP was beneficial for increasing the mean weight diameter of soil aggregates and alleviating the conversion of NH4+-N to NO3--N. Applying CAN alone or in combination with DMPP helped to increase plant yields and heavy metal extraction of both plant species, and effectively reduce soil heavy metal contents. The combined addition of CAN and DMPP decreased Neocosmospora and stimulated Papiliotrema growth to reduce N2O emissions from C. sulphureus soil. This treatment also inhibited the growth of Fusarium while promoted f_Micropepsaceae, f_Gaiellales, and 1921–3, Setophoma and Trichoderma to increase P. americanum × P. purpureum yield and reduce soil CO2 emissions. P. americanum × P. purpureum treated with both CAN and DMPP not only significantly improved the phytoremediation efficiency, but also achieved greenhouse gas emissions reduction, which provides scientific basis and promising methods for the integration of both aspects.