Comparison of nitrification inhibitors for mitigating cadmium accumulation in pakchoi and their associated microbial mechanisms

The use of nitrification inhibitors has been suggested as a strategy to decrease cadmium(Cd)accumulation in crops.However,the most efficient nitrification inhibitor for mitigating crop Cd accumulation remains to be elucidated,and whether and how changes in soil microbial structure are involved in this process also remains unclear.To address these questions,this study applied three commercial nitrification inhibitors,namely,dicyandiamide(DCD),3,4-dimethylpyrazole phosphate(DMPP),and nitrapyrin(NP),to pakchoi.The results showed that both DCD and DMPP(but not NP)could efficiently decrease Cd concentrations in pakchoi in urea-and ammonium-fertilized soils.In addition,among the three tested nitrification inhibitors,DMPP was the most efficient in decreasing the Cd concentration in pakchoi.The nitrification inhibitors decreased pakchoi Cd concentrations by suppressing acidification-induced Cd availability and reshaping the soil microbial structure;the most effective nitrification inhibitor was DMPP.Ammonia oxidation generates the most protons during nitrification and is inhibited by nitrification inhibitors.Changes in environmental factors and predatory bacterial abundance caused by the nitrification inhibitors changed the soil microbial structure and increased the potential participants in plant Cd accumulation.In summary,our study identified DMPP as the most efficient nitrification inhibitor for mitigating crop Cd contamination and observed that the soil microbial structural changes caused by the nitrification inhibitors contributed to decreasing Cd concentration in pakchoi.

SIMULATION OF THE IN-PILE BEHAVIORS EVOLUTION IN NUCLEAR FUEL RODS WITH THE IRRADIATION DAMAGE EFFECTS

Based on the commercial computational software, a three-dimensional finite ele- ment model to simulate the thermo-mechanical behaviors in a nuclear fuel rod is established; By taking into consideration irradiation-swelling of the pellet and the irradiation damage effects in the cladding together with the coupling effects between the temperature field and the mechanical field, the user subroutines to define the special material performance and boundary conditions have been developed independently and validated. Three-dimensional numerical simulation of the thermo-mechanical coupling behaviors in a nuclear fuel rod is carried out, and the evolution rules of the important thermal and mechanical variables are obtained and analyzed. The research re- sults indicate that： （i） the fuel pellets will be in contact with the cladding at high burnup, which will induce a strong mechanical interaction between them; （2） the irradiation creep effect plays an important role in the mechanical behavior evolution in the nuclear fuel rod.