The compound risk of decabromodiphenyl ethane and cadmium to soil nutrient cycling in agroecosystems: Linking the enzyme, microbial community, gene networks to plant stress.

Soil serves as the habitat for numerous organisms and is increasingly threatened from co-pollution of novel brominated flame retardant (NBFRs) and heavy metals (HMs). Focusing on Deca-bromodiphenyl ethane (DBDPE) and cadmium (Cd) as the targets, we constructed a soil-lettuce-earthworm microcosm to explore co-pollution effects in rhizosphere soils. Results showed that DBDPE increased bioavailable Cd fraction to amplified its ecological risks. Co-pollution significantly inhibited the expression of soil functional genes, especially C/N cycling genes, including pgu and abfA in C-cycling and narG, nirS, nirK and nosZ in N-cycling. Among these, impaired denitrification was verified with the increased NO3-N contents and nitrite reductase activity suppression. Meanwhile, the decreased sucrase activity and cation exchange capacity reflected C-cycling disruption, leading to a reduction in bioavailable C sources. In addition, co-pollution maximum damaged soil microbial structure, decreasing diversity and community stability. Ultimately, the pollutants accumulation in lettuce and exhibited potential food safety concerns. The interference of soil function damaged the lettuce quality with increased nitrate content and reduced soluble protein. Particularly, attention needs to be paid to the abnormal accumulation of NO3--N in soil. This study extended the current knowledge of ecological implication of NBFRs and HMs co-pollution in microcosm agroecosystems.