Mechanisms of urea combined with nitrification inhibitors on prompting cadmium uptake and accumulation in rape (Brassica napus L.)

Rape (Brassica napus L.) plants are promising candidate materials in the remediation of cadmium (Cd)-polluted farmland. However, there remains a noteworthy challenge to enhance the Cd accumulation capacity at rape production safely. Nitrification inhibitors (NIs) effectively improve nitrogen fertilizer utilization efficiency through regulating N forms. Scant information about the effects of NIs on rape Cd accumulation capacity and its mechanisms are still indistinct.

In this study, Cd uptake and accumulation in rape treated with dicyandiamide (DCD) and 3, 4-dimethylpyrazole phosphate (DMPP) under pot experiments, hydroponic experiments and field experiments were investigated.

Pot experiment results showed that NIs led to soil acidification, thereby elevating soil Cd bioavailability and rape Cd accumulation. Hydroponic experiments indicated that NIs increased the contents of pectin and hemicellulose 2 (HC2) in cell walls, altered the binding ability of Cd on cell wall and modified the Cd intracellular distribution. Furthermore, NIs up-regulated the transcription of Cd transporter genes, such as heavy metal ATPase (HMA) 2, HMA3, and HMA4 in the root, improved Cd tolerance and augmented Cd accumulation. Rape field experiment results demonstrated that NIs enhanced Cd phytoextraction efficiency.

This work provided a promising strategy for the application of NIs on promoting phytoremediation efficiency of Cd by oil crops in Cd-contaminated farmland.