Biological/Chemical nitrification inhibitors combined with urea enhance remediation efficiency of ornamental plants and reduce greenhouse gas emissions in heavy metal contaminated soils

Addressing the dual challenges of soil heavy metal (HM) contamination and agricultural greenhouse gas (GHG) emissions requires the development of synergistic management strategies. Nitrification inhibitors (NIs), widely used in nitrogen management, remain insufficiently studied in metal-impacted soils, particularly regarding their effects on GHG emissions and ornamental plant remediation. By planting two ornamental plants, Tagetes patula and Chrysanthemum × morifolium , this study compared the effects of the biological nitrification inhibitor (BNI, methyl 3-(4-hydroxyphenyl) propanoate) and the synthetic nitrification inhibitor (SNI, 3,4-dimethylpyrazole succinic acid) when used alone or in combination with urea. Results show that co-application of NIs with urea produced strong synergy, enhancing HM phytoextraction and reducing N₂O emissions and global warming potential (GWP). DMPSA combined with urea performed best in T. patula , while UM achieved near-zero emissions in C. morifolium . Applying NIs alone promoted metal sequestration in cell walls, reducing cytoplasmic toxicity. Remarkably, MHPP alone turned the C. morifolium soil into a net CH₄ sink, resulting in negative GWP and greenhouse gas intensity (GHGI). Species-specific enzyme responses further shaped these effects. This finding demonstrates that combining NIs with urea fertilization represents an effective strategy for integrated environmental management, improving phytoremediation performance while providing substantial climate co-benefits. Applying NIs (alone or combined with urea) promotes the growth and remediation efficiency of ornamental plants, aiding heavy metal reduction and landscape enhancement.