Combined addition of γ-PGA and DCD facilitates phytoremediation of heavy metals and carbon sequestration: A field experiment

A field study examined the impact of gamma-polyglutamic acid (gamma-PGA), both alone and in combination with dicyandiamide (DCD), on the phytoremediation of soil contaminated with Cd, Pb, and Zn. This study focused on the heavy metal (HM) accumulation, and soil CO2 and N2O emissions in Cosmos sulphureus and Pennisetum americanum x P. purpureum, and soil microbial communities. The findings indicated that the application of gamma-PGA, either alone or in combination with DCD, increased plant yield and HM bioavailability in the soil, leading to improved HM uptake by plants. For P. americanum x P. purpureum, compared to CK treatment, the combined addition of gamma-PGA and DCD increased the Cd, Pb, and Zn extraction by 131.4%, 80.6%, and 99.7%, respectively. Compared to gamma-PGA alone, the combined addition of gamma-PGA and DCD reduced the soil N2O emission and global warming potential by 26.4% and 39.1%, respectively. P. americanum x P. purpureum treated with gamma-PGA and DCD achieved C sequestration of 829 kg ha- 1. Moreover, the application of gamma-PGA, alone or in combination with DCD, increased the abundance of soil microbes. Bacteria (Proteobacteria, Actinobacteriota, and Firmicutes) as well as fungi (Basidiomycota and Mortierellomycota) contributed to HM accumulation and resistance to stress by altering soil enzyme activities, C and N fractions. Additionally, Acidobacteriota and Patescibacteria are beneficial to reducing soil GHG emissions and GWP in P. americanum x P. purpureum soil treated with gamma-PGA and DCD. In conclusion, P. americanum x P. purpureum with the combined addition of gamma-PGA and DCD increased HM extraction and total C sequestration in the plant-soil system. This approach offers a scientific basis and promising approach for integrating phytoremediation with C sequestration.