Effects of modified nanoscale carbon black on plant growth, root cellular morphogenesis, and microbial community in cadmium-contaminated soil

Previous researches have confirmed that modified nanoscale carbon black (MCB) can decrease the bioavailability of heavy metals in soil and accumulation in plant tissues, resulting in the increase of biomass of plant. However, as a nanoparticle, the effects of MCB on plant cell morphology and microbial communities in Cd-contaminated soil are poorly understood. This study, through greenhouse experiments, investigated the effects of MCB as an amendment for 5 mg·kg⁻¹ Cd-contaminated soil on plant growth, plant cellular morphogenesis, and microbial communities. Two types of plants, metal-tolerant plant ryegrass (Lolium multiflorum), and hyperaccumulator plant chard (Beta vulgaris L. var. cicla) were selected. The results indicated that adding MCB to Cd-contaminated soil, the dry biomass of shoot ryegrass and chard increased by 1.07 and 1.05 times, respectively, comparing with control group (the treatment without MCB). Meanwhile, the physiological characteristics of plant root denoted that adding MCB reduced the damage caused by Cd to plants. The acid phosphatase activity of soils treated with MBC was higher and the dehydrogenase activity was lower than control group during whole 50 days of incubation, while the urease and catalase activity of soils treated with MBC were higher than control group after 25 days of incubation. When compared with the treatment without MCB, the abundances of nitrogen-functional bacteria (Rhodospirillum and Nitrospira) and phosphorus-functional bacteria (Bradyrhizobium and Flavobacterium) increased but that of nitrogen-functional bacteria, Nitrososphaera, declined. The presence of MCB resulted in increased microbial community abundance by reducing the bioavailability of heavy metals in soil, while increasing the abundance of plants by increasing the amount of available nitrogen in soil. The result of this study suggests that MCB could be applied to the in-situ immobilization of heavy metal in contaminated soils because of its beneficial effects on plants growth, root cellular morphogenesis, and microbial community.