Microbiological Mechanisms of Collaborative Remediation of Cadmium-Contaminated Soil with Bacillus cereus and Lawn Plants.

Severe cadmium contamination poses a serious threat to food security and human health. Plant-microbial combined remediation represents a potential technique for reducing heavy metals in soil. The main objective of this study is to explore the remediation mechanism of cadmium-contaminated soil using a combined approach of lawn plants and microbes. The target bacterium Bacillus cereus was selected from cadmium-contaminated soil in mining areas, and two lawn plants (Festuca arundinacea A'rid III' and Poa pratensis M'idnight II') were chosen as the target plants. We investigated the remediation effect of different concentrations of bacterial solution on cadmium-contaminated soil using two lawn plants through pot experiments, as well as the impact on the soil microbial community structure. The results demonstrate that Bacillus cereus promotes plant growth, and the combined action of lawn plants and Bacillus cereus improves soil quality, enhancing the bioavailability of cadmium in the soil. At a bacterial suspension concentration of 105 CFU/mL, the optimal remediation treatment was observed. The removal efficiency of cadmium in the soil under Festuca arundinacea and Poa pratensis treatments reached 33.69% and 33.33%, respectively. Additionally, the content of bioavailable cadmium in the rhizosphere soil increased by up to 13.43% and 26.54%, respectively. Bacillus cereus increased the bacterial diversity in the non-rhizosphere soil of both lawn plants but reduced it in the rhizosphere soil. Additionally, the relative abundance of Actinobacteriota and Firmicutes, which have potential for heavy metal remediation, increased after the application of the bacterial solution. This study demonstrates that Bacillus cereus can enhance the potential of lawn plants to remediate cadmium-contaminated soil and reshape the microbial communities in both rhizosphere and non-rhizosphere soils.

Enhancing phytoremediation of cadmium and arsenic in alkaline soil by Miscanthus sinensis: A study on the synergistic effect of endophytic fungi and biochar.

Endophytic fungi (Trichoderma harzianum (TH) and Paecilomyces lilacinus (PL)) showed potential in phytoremediation for soils contaminated with potentially toxic elements (PTEs (Cd and As)). However, their efficiency is limited, which can be enhanced with the assistance of biochar. This study sought to investigate the effects of TH at two application rates (T1: 4.5 g m-2; T2: 9 g m-2), PL at two application rates (P1: 4.5 g m-2; P2: 9 g m-2), in conjunction with biochar (BC) at 750 g m-2 on the phytoremediation of PTEs by Miscanthus sinensis (M. sinensis). The results showed that the integration of endophytic fungi with biochar notably enhanced the accumulation of Cd and As in M. sinensis by 59.60 %-114.38 % and 49.91 %-134.60 %, respectively. The treatments T2BC and P2BC emerged as the most effective. Specifically, the P2BC treatment significantly enhanced the soil quality index (SQI > 0.55) across all examined soil layers, markedly improving the overall soil condition. It was observed that T2BC treatment could elevate the SQI to 0.56 at the 0-15 cm depth. The combined amendment shifted the primary influences on plant PTEs accumulation from fungal diversity and soil nutrients to bacterial diversity and the availability of soil PTEs. Characteristic microorganisms identified under the combined treatments were RB41 and Pezizaceae, indicating an increase in both bacterial and fungal diversity. This combination altered the soil microbial community, influencing key metabolic pathways. The combined application of PL and biochar was superior to the TH and biochar combination for the phytoremediation of M. sinensis. This approach not only enhanced the phytoremediation potential but also positively impacted soil health and microbial community, suggesting that the synergistic use of endophytic fungi and biochar is an effective strategy for improving the condition of alkaline soils contaminated with PTEs.

Combination of Biochar and Trichoderma harzianum Can Improve the Phytoremediation Efficiency of Brassica juncea and the Rhizosphere Micro-Ecology in Cadmium and Arsenic Contaminated Soil.

Phytoremediation is an environment-friendly method for toxic elements remediation. The aim of this study was to improve the phytoremediation efficiency of Brassica juncea and the rhizosphere soil micro-ecology in cadmium (Cd) and arsenic (As) contaminated soil. A field experiment was conducted with six treatments, including a control treatment (CK), two treatments with two contents of Trichoderma harzianum (T1: 4.5 g m-2; T2: 9 g m-2), one biochar treatment (B: 750 g m-2), and two combined treatments of T1B and T2B. The results showed Trichoderma harzianum promoted the total chlorophyll and translocation factor of Brassica juncea, while biochar promoted plant biomass compared to CK. T2B treatment showed the best results, which significantly increased Cd accumulation by 187.49-308.92%, and As accumulation by 125.74-221.43%. As a result, the soil's total Cd content was reduced by 19.04% to 49.64% and total As contents by 38.76% to 53.77%. The combined amendment increased the contents of soil available potassium, phosphorus, nitrogen, and organic matter. Meanwhile, both the activity of glutathione and peroxidase enzymes in plants, together with urease and sucrase enzymes in soil, were increased. Firmicutes (dominant bacterial phylum) and Ascomycota (dominant fungal phylum) showed positive and close correlation with soil nutrients and plant potentially toxic elements contents. This study demonstrated that phytoremediation assisted by biochar and Trichoderma harzianum is an effective method of soil remediation and provides a new strategy for enhancing plant remediation efficiency.