There is currently increasing pressure on agriculture to simultaneously remediate soil and ensure safe agricultural production. In this study, we investigate the potential of a novel combination of biochar and plant growth-promoting bacteria (PGPB) as a promising approach. Two types of biochar, corn stover and rice husk-derived, were used in combination with a PGPB strain, Bacillus sp. PGP5, to remediate Cd and Pb co-contaminated soil and enhance lettuce performance. The contaminated soil was pre-incubated with biochar prior to PGP5 inoculation. The combined application of biochar and PGPB reduced the diethylenetriaminepentaacetic acid (DTPA) -extractable Cd and Pb concentrations in the soil by 46.45%-55.96% and 42.08%-44.83%, respectively. Additionally, this combined application increased lettuce yield by 23.37%-65.39% and decreased Cd and Pb concentrations in the edible parts of the lettuce by 57.39%-68.04% and 13.57%-32.50%. The combined application showed a better promotion on lettuce growth by facilitating chlorophyll synthesis and reducing oxidative stress. These demonstrated a synergistic effect between biochar and PGPB. Furthermore, our study elucidated the specific role of the biochar-PGPB combination in soil microbial communities. Biochar application promoted the survival of PGP5 in the soil. The impact of biochar or PGPB on microbial communities was found to be most significant in the early stage, while the development of plants had a greater influence on rhizosphere microbial communities in later stage. Plants showed a tendency to recruit plant-associated microbes, such as Cyanobacteria, to facilitate growth processes. Notably, the combined application of biochar and PGPB expedited the assembly of microbial communities, enabling them more closely with the rhizosphere microbial communities in late stage of plant development and thus enhancing their effects on promoting plant growth. This study highlights the \"accelerating\" advantage of the biochar-PGPB combination in the assembly of rhizosphere microbiomes and offers a new strategy for simultaneous soil remediation and safe agricultural production.

Although oilseed rape is frequently used as an alternative planting crop in the phytoremediation of cadmium (Cd)-contaminated agricultural land, methods for screening excellent oilseed rape varieties in this regard are inadequate. Herein, we developed a screening method that incorporates Cd accumulation, distribution, and removal, economic output, adaptability to Cd-contaminated agricultural land, and trace element variation. A Cd-adaptability index (Cd-AI) based on 10 agronomic traits was used to measure the adaptability of varieties to Cd-contaminated agricultural land. Moreover, to simplify the evaluation of adaptability, yield, biomass, and pod number with high weightings were selected to construct a discriminant function for Cd-contaminated agricultural land adaptability (correctly classified 94.20%). In a 2 year field trial, we evaluated 225 oilseed rape varieties, among which we identified two promising low-Cd-accumulating and two Cd-remediating varieties. For the low-Cd-accumulating varieties (HuYou17 and DeXingYou558), we obtained grain bioaccumulation factor (BAF) values of 0.07 and 0.08, BAFsoil-stalk values of <1, and economic outputs of RMB 25,054 and 32,292 yuan hm-2, respectively. Similarly, the Cd-remediating varieties (ZaoZa8 and YuYou61) were characterized by BAFsoil-stalk values of 4.65 and 3.61, BAFsoil-grain values of 0.16 and 0.16, Cd removals of 69.02 and 58.25 g hm-2, and economic outputs of RMB 31,189 and 24,962 yuan hm-2, respectively. Compared with the control variety, we detected lower uptakes of multiple trace elements (3-43%) in the low-Cd-accumulating varieties, whereas the Cd-remediating varieties were characterized by 15.40% and 8.30% increases in the accumulation of magnesium and zinc, respectively. Our findings augment the evaluation indices used for evaluating oilseed rape varieties and provide valuable insights from the perspectives of varietal screening and promotional application. The effective varieties identified have application potential for safe production and the remediation of agricultural land without interrupting annual agricultural production, and provide an economically sustainable approach for the utilization of Cd-contaminated agricultural land.

A plot experiment was carried out to assess the applicability of soil conditioners on Cd-polluted acidic paddy fields. The effects of five soil conditioners[Tianxiang 1 Hao (TX1), limestone (Li), silicon fertilizer, Nuodikang (NDK), and calcium magnesium phosphate fertilizer (CaMg-P)] on Cd accumulation and transport between contaminated soil and rice plants and rice yield on the land were analyzed. The results showed that compared with that under the control, other tested methods increased soil pH by 0.41-0.68 units and decreased available Cd content in the soil by 11.2%-39.7%. The difference between Li- and NDK-treated soil available Cd reached a significant level (P < 0.05). ② Compared with that in the blank control, the application of soil conditioner could significantly reduce the total amount of Cd in rice, and the Cd content in roots, other leaves, rachises, chaffs, and brown rice were significantly lower than those in the CK treatment (P < 0.05). The Cd translation factor between various sites was shown as TFroots-other nodes > TFroots-first nodes > TFroots-rachises > TFroots-chaffs ≈ TFroots-flag leaves > TFroots-brown rice. The Cd content of brown rice met the national safety standard (0.2 mg·kg-1), in which the TX1, Li, and CaMg-P treatments showed significant Cd reduction effects, and ω(Cd) was 0.097, 0.094, and 0.134 mg·kg-1, respectively. ③ The application of soil conditioner could increase the yield by 9.9%-35.8%, and the yield of the CaMg-P and TX1 treatments was significantly higher than that of other treatments (P < 0.05). ④ Correlation analysis showed that the Cd content in brown rice was significantly positively correlated with available Cd content in soil, available Fe content in soil, and available phosphorus but negatively correlated with soil pH. In summary, TX1 and CaMg-P are recommended to be applied in farmland lightly polluted by the heavy metal Cd to ensure the safety of agricultural products.

Arsenic (As) and cadmium (Cd) are the most common toxic and harmful heavy metal elements in paddy soils and are easily transferred from the soil to grains. At present, As and Cd and their co-contamination in paddy soils in China are widespread, posing a serious threat to food security and human health. As and Cd have opposite environmental behaviors in soil, and the simultaneous remediation of co-contamination with As and Cd is a current technical difficulty for safe rice production. This review focuses on several practical techniques for simultaneous mitigation of As and Cd uptake and transport in rice in recent years, including water management, passivation, drenching techniques, electrokinetic remediation, phytoremediation, selection of low-accumulation rice varieties, and foliar spraying application. The treatment effects, mechanisms of action, and constraints of various technologies are summarized and analyzed; the development direction of the main barrier control technologies is proposed and the importance of constructing a comprehensive technology model with high regional adaptability is emphasized to provide a reference for the remediation of co-contamination with As and Cd in paddy and safe rice production.

The utilization of Cd-contaminated soil in vegetable crop production can lighten the food crisis and improve the soil environmental resilience. Intercropping is a reliable technology in safety production from contaminated soil. A field-scale experiment was carried out to unravel how plant species and pattern affect the growth and Cd uptake of Chinese cabbage from Cd contaminated land. Among all the intercropping systems designed in this study, one row of Chinese cabbage intercropping with one row of Solanum nigrum L. is the best planting mode (high yields (2.78 kg/m2) and low Cd accumulation (0.02 mg/kg) of Chinese cabbage). Combined with the in-depth joint analysis of diverse soil physicochemical features (soil nutrient characteristics and microbial community structure), biomass yield and quality, and soil microbiological properties, we elaborated that two measures (screening hyperaccumulation types and controlling planting strip width) were the major factors in determining the growth of the aboveground and underground parts of Chinese cabbage respectively, thus directly regulating the application effectiveness of intercropping technology. The intertwined mechanisms (interspecific and intraspecific relationship) of different intercropping systems are summarized, which include better utilization of space, light and other resources in the aboveground part, bioavailability of nutrient, drive of soil bacteria and alleviated soil Cd stress in the underground part, etc. Our research outputs indicate the effectiveness and feasibility of intercropping can be improved by optimizing the streamline configuration and plant mode, which provide theory of reference and practical evidence for warranting the food safety and agricultural soil remediation simultaneously.

The relationship between iron manganese plaque (IP) and cadmium (Cd) accumulation by rice in the microenvironment of rice rhizosphere at varying field scales needs to be further explored. In this study, we selected different rice varieties and implemented tailored amendments to ensure the safe production of rice grains in heavily Cd-contaminated farmland situated around an E-waste dismantling site. Through regional surveys, we elucidated the role of IP in facilitating safe rice production. The selection of low-Cd accumulating rice varieties and application of appropriate amendments with sufficient dosages allowed for the effective reduction of Cd transport from soil to rice, resulting in a safe concentration of Cd in rice grains. Analysis using a random forest algorithm indicated that iron (Fe) played a more pivotal role than manganese in soil-rice systems in mitigating Cd accumulation in brown rice. The presence of Fe in IP (IP-Fe) at a low loading mass was unfavorable to the Cd-safe production of rice, while at an IP-Fe loading mass of 52 g/kg, the Cd content in brown rice decreased to a safe level. Furthermore, precipitation, coprecipitation, and complexation of surface functional groups contributed to Cd fixation on IP, as indicated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, electron probe microanalysis, and Fourier-transform infrared spectroscopy with attenuated total reflection. Our results highlighted the key role of IP in the production of Cd-safe rice at different field scales.

A crop rotation system combining agricultural production with phytoremediation is an economical and sustainable method of remediation of cadmium (Cd)-contaminated farmland. This study focuses on migration and transformation of Cd in rotation systems and the influencing factors. In a two-year field experiment, four rotation systems were evaluated: traditional rice and oilseed rape (TRO), low-Cd rice and oilseed rape (LRO), maize and oilseed rape (MO), and soybean and oilseed rape (SO). Oilseed rape is a remediation plant in rotation systems. Compared to 2020, the grain Cd concentrations of traditional rice, low-Cd rice, and maize in 2021 decreased by 73.8%, 65.7%, and 24.0% (below the safety limits), respectively. However, soybean increased by 71.4%. The LRO system featured the highest oil content of rapeseed (about 50%) and economic output/input ratio (1.34). Removal efficiency of total Cd in soil was 10.03% (TRO) > 8.3% (LRO) > 5.32% (SO) > 3.21% (MO). Crop uptake of Cd was influenced by bioavailability of soil Cd, and soil environmental factors regulated the bioavailable Cd. Redundancy analysis (RDA) indicated that soil nitrate‑nitrogen (NO3--N) had a dominant impact on bioavailable Cd in soil, with variance contributions of 56.7% for paddy-upland (TRO and LRO) and 53.5% for dryland (MO and SO) rotation systems. The difference reflected that ammonium N (NH4+-N) was a secondary factor in paddy-upland rotations, while it was the available phosphorus (P) in dryland rotations, with variance contributions of 10.4% and 24.3%, respectively. The comprehensive evaluation of crop safety, production, economic benefits, and remediation efficiency revealed that the LRO system was efficient and more acceptable to local farmers, providing a new direction for the utilization and remediation of Cd-contaminated farmland.

To explore the effect and persistent effect of thiolated montmorillonite (TM) on safe production in cadmium (Cd) contaminated cropland, a two-year field experiment was conducted with different application amounts of TM. By adding to highly contaminated soils containing 2.46-3.81 mg·kg-1 Cd with no replenishment, the impacts of TM on concentrations of Cd in different parts of rice and available Cd in soils were investigated. The results showed that TM could significantly reduce the contents of Cd in brown rice as well as the contents and proportions of available Cd in soils, and its persistent effects on the passivation of Cd were obvious. After applying 0.5% or 1% TM to soils, the contents of Cd in different parts of the rice decreased significantly in the first season compared with that in the control. The contents of Cd in brown rice in the first season decreased to 0.16 mg·kg-1 and 0.08 mg·kg-1, respectively, by 84.0% and 91.9% compared with that of the control (0.98 mg·kg-1). Contents of Cd in brown rice were significantly lower than the maximum allowable amount (0.2 mg·kg-1) set by China (GB 2762-2017). Under the 0.5% and 1% treatments, the contents of Cd in brown rice of the subsequent three seasons under successive planting decreased by 50.2%-67.8% and 56.0%-81.6%, respectively, which were within the allowable amount. The proportions of available Cd in soils in the first season decreased from 48.4% under the control to 27.9% and 18.4%, respectively, which decreased by 20.5% and 29.9% under the 0.5% and 1% treatments. Compared with that in the control, proportions of available Cd in soils of the following three seasons decreased by 10.0%-17.1% and 12.4%-20.8%. There was a significant positive correlation between available Cd contents in soils and Cd contents in various parts of the rice. TM mainly reduced available Cd contents in soils, then reduced the absorption and accumulation of Cd in rice. The results of the two-year field experiment showed significant and continuous effects of TM on inhibiting Cd uptake by rice, which could be applied to the safe production in heavily Cd contaminated cropland.

A low-cost practical technology is urgently needed to minimize cadmium (Cd) pollution in rice in many parts of the world. In the present study, we elucidated the effects and mechanisms of four alkaline compound materials via field experiments in southern China. The results indicated that these two alkaline Si-rich compound materials (AF-SC, alkaline fertilizer compounded with Si-Ca mineral powder; AF-SS, AF compounded with Si-Se mineral powder) could achieve multi-objective gains by simultaneously reducing grain Cd, increasing yield and improving soil quality at a lower cost. The grain Cd content was decreased by an average of about 75% in two field sites, which even ensured safe grain production in areas with medium Cd pollution. The rice yield was increased by a range of 6.7%-21.0% for different varieties and sites. Moreover, the materials abated soil acidification with the increase of 0.36-0.62 pH units, increased the contents of available P and available Si, subsequently reducing available Cd content in soils. Structural equation model and regression analysis showed that the alkaline environment provided by the alkaline components in compound materials effectively inhibited the formation of Fe/Mn plaques on the root surface, reducing the uptake of Cd from the environment. In addition, the decrease in grain Cd was also attributed to the inhibition of Cd translocation from root to stem, mainly caused by the increase of available Si. These findings reveal that the base application of such alkaline Si-rich compound materials is a viable solution for the remediation of Cd-polluted paddy fields in south China.

In recent years, research on the safe utilization and green remediation of contaminated soil by intercropping has become common. In this study, the growth of an intercropping system of Luffa cylindrica-Semen cassiae in soil contaminated with medium amounts of arsenic (As) was studied using field (91.60 mg kg-1) and pot (83.34 mg kg-1) experiments. The field experiments showed that intercropping significantly increased the yield per plant of L. cylindrica by 27.36%, while the yield per plant of S. cassiae decreased by 21.66%; however, this difference was not significant. Intercropping reduced the concentration of As in all organs of L. cylindrica but increased the concentration of As in all parts of S. cassiae. The accumulation of As per plant of L. cylindrica was reduced by 20.72%, while that in a single plant of S. cassiae was increased by 201.93%. In addition, the concentration of As in the fruit of these two crops in these two planting modes was low enough to meet the National Food Safety Standard of China (GB2762-2017). In addition, the land equivalent ratio and As metal removal equivalent ratio of the intercropping mode was 1.03 and 2.34, indicating that the intercropping mode had advantages in land use and As removal. In the pot experiment, the biomass and As concentration of L. cylindrica and S. cassiae were roughly consistent with those in the field experiment. During the sampling period, intercropping reduced the concentration of As in the rhizosphere soil solution of L. cylindrica by 3.1-23.77%, while it increased the concentration of As in the rhizosphere soil solution of S. cassiae by 13.30-59.40%. The changes in pH and redox potential were also closely related to the content of water-soluble As in the rhizosphere environment, which affects the absorption of As by plants. In general, the L. cylindrica-S. cassiae intercropping system is a planting mode that can effectively treat soil that is moderately contaminated with As and remove it from the soil to an extent.