Chromium Pollution and Mitigation in a Sunflower Farmland System

Chromium is a major heavy metal pollutant that affects the health of both plants and animals. In this study, sunflower seedlings were treated with K2Cr7O4 containing 50, 100, and 250 mg of pure chromium per kilogram of soil. It was found that the chromium was absorbed by the roots and transported within plant tissues to the stems and leaves. Chromium affected sunflower photosynthesis, seen in increased the Fv/Fm values as the chromium concentration rose. Metagenomic sequencing of rhizosphere microbial communities after treatment with 100 mg/kg pure chromium indicated that the rhizosphere microorganisms were resistant to chromium exposure; chromium was found to promote dopamine secretion and chromium complexation by the microorganisms. In addition, chromium was found to reduce microbial production of N2O reductase and increase the emission of the greenhouse gas N2O. In addressing the problem of chromium pollution in sunflower farmland, Bacillus sp. strain C8 was isolated and shown to effectively reduce soil chromium contents and chromium absorption by sunflower, thereby reducing the adverse effects of the metal. Furthermore, a gene associated with chromium resistance, LOC118480906, was identified by transcriptome sequencing of sunflower plants. In conclusion, the findings denonstrate: (1) the effect of chromium exposure on sunflower growth and development of sunflower; (2) the ecological effects of chromium exposure on sunflower farmland; (3) the regulation of soil microbes and the identification of resistance associated genes are effective ways to reduce chromium pollution.