Inoculation of Cd-contaminated paddy soil with biochar-supported microbial cell composite: A novel approach to reducing cadmium accumulation in rice grains.

Bioremediation of heavy metal-contaminated soil using metal-resistant microbes is a promising remediation technology. However, as exogenous bacteria sometimes struggle to survive and grow when introduced to new soils, it is important to develop appropriate carriers for microbial populations. In this study, we report a novel approach to remediating Cd-contaminated rice paddy soil using biochar-supported microbial cell composites (BMCs) produced from agricultural waste (cornstalks). Pot experiments showed that amendment with BMC was more efficient at reducing root and grain Cd content than pure bacteria, while improving soil Cd fractionation toward more stabilized and less labile forms. Bacteria in the BMC medium grew more readily with more abundant metabolites than those raised in free cells, probably because biochar provides shelter via porous structures (as confirmed by scanning electron microscopy) as well as additional nutrients. Overall, the improved long-term production of microbial biomass caused by BMC inoculation results in a higher remediation efficiency. Our results demonstrate the feasibility of using biochar as an appropriate carrier for metal-tolerant bacteria to remediate Cd-contaminated paddy fields.

[Effect of Conditioning Agent Combined with Flooding Measures on Absorption and Accumulation of Cadmium in Rice].

In order to evaluate the effects and mechanisms of flooding measures, soil conditioner, silicon mineral fertilizer and sprayed foliar fertilizer, gypsum powder, and their multiple treatments for reducing Cd accumulation in rice grown in Cd-contaminated soil. A plot experiment was conducted in three different Cd-contaminated soils. The results showed that flooding measures, a single application of conditioning agents, and combined application and flooding treatment can reduce soil-available Cd and the Cd content in various organs of rice with 6.58%-30.01% reduction in soil available-Cd and 12.64%-68.68% reduction in Cd content in brown rice, respectively. The Cd reduction decreased in the following order:comprehensive treatment (T6) > basic application of gypsum powder (T5) > base Xiangrunbang state soil conditioner (T3) > mineral silicon fertilizer and spray foliar fertilizer (T4) > flood treatment (T2). In addition, the average value of the reduction effect of the Cd content in brown rice was calculated. The five treatments in the experiment reduced the enrichment of various parts of the rice, which is a main reason for the decrease in Cd content in the brown rice. According to the field plot test, the combined application of the basic conditioning agent, mineral silicon fertilizer, and sprayed foliar fertilizer, and gypsum powder and flooding measures can be used as an effective method for Cd pollution control in Cd-contaminated cultivated rice.