The adsorption-diffusion model and biomimetic simulation reveal the switchable roles of silicon in regulating toxic metal uptake in rice roots.

Soil contamination by heavy metals has become a serious threat to global food security. The application of silicon (Si)-based materials is a simple and economical method for producing safe crops in contaminated soil. However, the impact of silicon on the heavy-metal concentration in plant roots, which are the first line in the chain of heavy-metal entering plants and causing stress and the main site of heavy-metal deposition in plants, remains puzzling. We proposed a process-based model (adsorption-diffusion model) to explain the results of a collection of 28 experiments on alleviating toxic metal stress in plants by Si. Then we evaluated the applicability of the model in Si-mitigated trivalent chromium (Cr[III]) stress in rice, taking into account variations in experimental conditions such as Cr(III) concentration, stress duration, and Si concentration. It was found that the adsorption-diffusion model fitted the experimental data well (R2 > 0.9). We also verified the binding interaction between Si and Cr in the cell wall using SEM-EDS and XPS. In addition, we designed a simplified biomimetic device that simulated the Si in cell wall to analyze the dual-action switch of Si from increasing Cr(III) adsorption to blocking Cr(III) diffusion. We found that the adsorption of Cr(III) by Si decreased from 58% to 7% as the total amount of Cr(III) increased, and finally the diffusion blocking effect of Si dominated. This study deepens our understanding of the role of Si in mitigating toxic metal stress in plants and is instructive for the research and use of Si-based materials to improve food security.

Co-foliar application of zinc and nano-silicon to rice helps in reducing cadmium exposure risk: Investigations through in-vitro digestion with human cell line bioavailability assay.

Foliar application of zinc (Zn) or silicon nanoparticles (Si-NPs) may exert regulatory effects on cadmium (Cd) accumulation in rice grains, however, their impact on Cd bioavailability during human rice consumption remains elusive. This study comprehensively investigated the application of Zn with or without Si-NPs in reducing Cd accumulation in rice grains as well to exactly evaluate the potential risk of Cd exposure resulting from the rice consumption by employing field experiment as well laboratory bioaccessibility and bioavailability assay. Sole Zn (ZnSO4) or in combination with Si (ZnSO4 +Si and ZnO+Si) efficiently lowered the Cd concentration in rice grains. However, the impact of bioaccessible (0.1215-0.1623 mg kg-1) and bioavailable Cd (0.0245-0.0393 mg kg-1) during simulated human rice consumption depicted inconsistent trend. The straw HCl-extractable fraction of Cd (FHCl-Cd) exhibited a significant correlation with total, bioaccessible, and bioavailable Cd in grains, indicating the critical role of FHCl-Cd in Cd accumulation and translocation from grains to human. Additionally, foliar spraying of Zn+Si raised the nutritional value of rice grains, leading to increased protein content and reduced phytic acid concentration. Overall, this study demonstrates the potential of foliar application of ZnSO4 +Si in mitigating the Cd levels in rice grains and associated health risks upon consumption.

Seed nano-priming with multiple nanoparticles enhanced the growth parameters of lettuce and mitigated cadmium (Cd) bio-toxicity: An advanced technique for remediation of Cd contaminated environments.

Seed nano-priming can be used as an advanced technology for enhancing seed germination, plant growth, and crop productivity; however, the potential role of seed nano-priming in ameliorative cadmium (Cd) bio-toxicity under Cd stress has not yet been sufficiently investigated. Therefore, in this study we investigated the beneficial impacts of seed priming with low (L) and high (H) concentrations of nanoparticles including nSiO2 (50/100 mg L-1), nTiO2 (20/60 mg L-1), nZnO (50/100 mg L-1), nFe3O4 (100/200 mg L-1), nCuO (50/100 mg L-1), and nCeO2 (50/100 mg L-1) on lettuce growth and antioxidant enzyme activities aiming to assess their efficacy for enhancing plant growth and reducing Cd phytotoxicity. The results showed a significant increase in plant growth, biomass production, antioxidant enzyme activities, and photosynthetic efficiency in lettuce treated with nano-primed nSiH + Cd (100 mg L-1), nTiH + Cd (60 mg L-1), and nZnL + Cd (50 mg L-1) under Cd stress. Moreover, nano-priming effectively reduced the accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) in lettuce shoots. Interestingly, nano-primed nSiH + Cd, nTiH + Cd, and nZnL + Cd demonstrated efficient reduction of Cd uptake, less translocation factor of Cd with high tolerance index, ultimately reducing toxicity by stabilizing the root morphology and superior accumulation of critical nutrients (K, Mg, Ca, Fe, and Zn). Thus, this study provides the first evidence of alleviating Cd toxicity in lettuce by using multiple nanoparticles via priming strategy. The findings highlight the potential of nanoparticles (Si, Zn, and Ti) as stress mitigation agents for improved crop growth and yield in Cd contaminated areas, thereby offering a promising and advanced approach for remediation of Cd contaminated environments.

Assessing the effectiveness of 3, 4-dimethylpyrazole phosphate (DMPP) inhibitor in mitigating N2O emissions from contrasting Cd-contaminated soils.

Improving nitrogen use efficiency of chemical fertilizers is essential to mitigate the negative environmental impacts of nitrogen. Nitrification, the conversion of ammonium to nitrate via nitrite by soil microbes, is a prominent source of nitrogen loss in soil systems. The effectiveness of nitrification inhibitors in reducing nitrogen loss through inhibition of nitrification is well-documented, however, their efficacy in heavy metals-contaminated soils needs thorough investigations. The current study assessed the efficacy of nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) in reducing nitrous oxide (N2O) emissions in cadmium (Cd) contaminated paddy and red soils under lab-controlled environment. Obtained results indicated the substantial reduction in N2O emissions with DMPP in paddy and red soil by 48 and 35 %, respectively. However, Cd contamination resulted in reduced efficacy of DMPP, thus decreased the N2O emissions by 36 and 25 % in paddy and red soil, respectively. It was found that addition of DMPP had a significant effect on the abundance of ammonia oxidizing bacteria (AOB) and archaea (AOA). Notably, the reduction in N2O emissions by DMPP varied with the abundance of AOB. Moreover, Cd pollution resulted in a significant (P < 0.05) reduction in the abundance of archaeal and bacterial amoA genes, as well as bacterial nirK, nirS, and nosZ genes. The combined treatment of Cd and DMPP had a detrimental impact on denitrifiers, thereby influencing the overall efficiency of DMPP. These findings provide novel insights into the application of DMPP to mitigate nitrification and its potential role in reducing N2O emissions in contaminated soils.

Current situation of "non-grain production" of cultivated land in China and the research progress of re-tillage and fertilization technology.

In recent years, the influx of business capital to rural areas, land transfer and adjustment in planting structure have led to the widespread of "non-grain production" of cultivated land in China, which threatens the "1.8 billion mu of arable land protection red line" as well as national food security. Both tillage layer stripped and unstripped are examples of "non-grain production" of cultivated land, which are detrimental to long-term food security because they might reduce soil fertility to varied degrees. In the former case, the original topsoil has been destroyed and the tillage layer is gone. In the latter, there may be impediments such as acidification and salinization. Domestic and international scholars have conducted extensive research on the improvement of degraded soils, including measures with guest soil and soil replacement, the reduction of soil barrier factors, biological fertilization and other measures. There are no systematic research results on the remediation of "non-grain production" of cultivated land. Using data from the National Statistical Yearbook data and literature analysis, we systematically summarized current status of "non-grain production" of cultivated land and key technologies for land improvement, recultivation and fertilization in China, and put forward future directions in this area.

Effect of foliar application of nanoparticles on growth, physiology, and antioxidant enzyme activities of lettuce (Lactuca sativa L.) plants under cadmium toxicity.

Nanotechnology has attracted the interest of scientists due to its wide range of application specifically in agriculture. Nanoparticles (NPs) may act as a promising materials to alleviate cadmium (Cd) stress in plants. This study aims to assess the impact of multiple nanoparticles including nSiO2 (50 mg L-1:100 mg L-1), nTiO2 (20 mg L-1:60 mg L-1), nZnO (50 mg L-1:100 mg L-1), nFe3O4 (100 mg L-1:200 mg L-1), nCuO (50 mg L-1:100 mg L-1), and nCeO2 (50 mg L-1:100 mg L-1) in combination with CdCl2 (5 µM) to mitigate Cd toxicity in lettuce through foliar application in hydroponic solution. Current findings indicate that foliar application of nSiL + Cd (50 mg L-1), nZnL + Cd (50 mg L-1), and nTiL + Cd (20 mg L-1) is more effective in improving growth, biomass, root architecture, and elevated photosynthetic efficiency, which might be attributed to the increasing uptake of essential micronutrient (K, Mg, Ca, Fe, Zn) under Cd stress. Similarly, treatment with nanoparticles leads to reduced accumulation of ROS and MDA in lettuce, while enhancing the SOD, POD, CAT, and APX activities. The results showed that nanoparticles have high tolerance against Cd as depicted by the inhibition in Cd accumulation by 3.2-58% and 10-72% in roots as well as edible parts of lettuce, respectively. In addition, Cd alone reduces the morphological traits, antioxidant enzyme activity, and photosynthetic activity, while increasing the ROS, MDA, and Cd accumulation in lettuce. This comprehensive study suggests the role of nanoparticles in reducing Cd toxicity in lettuce, signifying their importance as stress mitigation agents. However, long-term pot, priming, and field trials are needed to identify the optimal nanoparticle for the lettuce under variable environmental conditions.

Effects of different remediation methods on phosphorus transformation and availability.

The effects of different heavy metal pollution remediation methods on soil nutrient transformation and soil health remain unclear. In this study, the effects of phytoextraction (PE) and passivation remediation (PR) on Cd-polluted soil phosphorus transformation and availability were compared by pot experiment. The results showed that PE significantly reduced the concentrations of total and available Cd (both H2O-Cd and DTPA-Cd) in soil, PR also decreased available Cd content but had no significant effect on total Cd content. PE slightly increased soil pH and NH4+-N content, while PR significantly increased soil pH, NO3--N and AK content. PE promoted the conversion of stable P (including HCl-Pi and residual-Pt), and increased the content of labile P (including H2O-Pi, NaHCO3-Pi and NaHCO3-Po) and the proportion of moderately labile P (including NaOH-Pi and NaOH-Po), while PR showed the opposite trend. PE showed a higher soil phoC gene abundance and acid phosphatase (ACP) activity, while PR showed a higher phoD gene copies and alkaline phosphatase (ALP) activity. Soil bacteria and phoD-harboring bacteria community was significantly affected by remediation methods and soil types. Compared with PR, PE reduced phoD-harboring bacterial diversity but significantly increased the abundance of genera associated with P dissolution (Streptomyces) and P conversion (Bradyrhizobium and Frankia), both of which were significantly positively correlated with labile P or moderately labile P. In general, compared with PR, PE can effectively remove soil Cd pollution, while maintaining a higher content of labile P and a higher proportion of moderately labile P, which can be considered as a green and sustainable remediation strategy conducive to soil quality.

From promoting aggregation to enhancing obstruction: A negative feedback regulatory mechanism of alleviation of trivalent chromium toxicity by silicon in rice.

Trivalent chromium [Cr(III)] is a threat to the environment and crop production. Silicon (Si) has been shown to be effective in mitigating Cr(III) toxicity in rice. However, the mechanisms by which Si reduces Cr(III) uptake in rice are unclear. Herein, we hypothesized that the ability of Si to obstruct Cr(III) diffusion via apoplastic bypass is related to silicic acid polymerization, which may be affected by Cr(III) in rice roots. To test this hypothesis, we employed hydroponics experiments on rice (Oryza sativa L.) and utilized apoplastic bypass tracer techniques, as well as model simulations, to investigate 1) the effect of Si on Cr(III) toxicity and its obstruction capacity via apoplastic bypass, 2) the effect of Cr(III) on silicic acid polymerization, and 3) the relationship between the degree of silicic acid polymerization and its Cr(III) obstruction capacity. We found that Si reversed the damage caused by Cr(III) stress in rice. Si exerted an obstruction effect in the apoplast, significantly decreasing the share of Cr(III) uptake via the apoplastic bypass from 18% to 11%. Moreover, Cr(III) reduced silica particles' radii and increased Si concentration in roots. Modeling revealed that a 5-fold reduction in their radii decreased the diffusion of Cr(III) in apoplast by approximately 17%. We revealed that Cr(III) promoted silicic acid polymerization, resulting in the formation of a higher number of Si particles with a smaller radius in roots, which in turn increased the ability of Si to obstruct Cr(III) diffusion. This negative feedback regulatory mechanism is novel and crucially important for maintaining homeostasis in rice, unveiling the unique role of Si under Cr(III) ion stress and providing a theoretical basis for promoting the use of Si fertilizer in the field.

Cadmium mobility and health risk assessment in the soil-rice-human system using in vitro biaccessibility and in vivo bioavailability assay: Two year field experiment.

Humans are mainly exposed to cadmium (Cd) due to the rice consumption, however there exist considerable differences across rice cultivars in terms of Cd absorption and accumulation in the grains, and subsequent release after digestion (bioaccessibility), as well as uptake by Caco-2 cells of humans (bioavailability). This study comprised of field and lab simulation trials where in the field, firstly 39 mid-rice cultivars were screened for their phytoremediation potential coupled with safe production in relation to uptake and translocation of Cd. Lower Cd concentrations (˂0.2 mg kg-1) in polished rice of 74 % cultivars were ascribed to the increased root to straw translocation indicating that straw may acquire higher accumulation of Cd. Furthermore, the ionomic profile demonstrated that the spatial distribution of metals in different rice organs corresponds to the plant growth morphology. In the second year, in vitro-in vivo assay model was employed to assess the bioaccessibility and bioavailability of Cd in polished rice and to further estimate the daily Cd intake by humans through rice grains. The results of bioaccessibility and bioavailability assays and daily estimated Cd intake presented the corresponding values of 39.02-59.76 %, 8.69-24.26 %, and 0.0185-0.9713 µg kg-1 body weight day-1, respectively. There exists a strong connection between total Cd and bioaccessible Cd to humans (R2 = 0.94, P < 0.01). Polynomial fitting (R2 = 0.91, P < 0.01) showed a better statistically significant correlation between total Cd contents and bioavailable levels, suggesting that in vitro-in vivo assays should be considered in future studies. The results of field experiments and in vitro-in vivo assays recommended the Tianyouhuazhan (MR-29), Heliangyou1hao (MR-17), and Yongyou15 (MR-1) as suitable mid-rice cultivars for the phytoremediation of slightly Cd contaminated soils coupled with rice agro-production due to their high nutritional value and low total and bioavailable Cd for human.

Niche Differentiation Among Canonical Nitrifiers and N2O Reducers Is Linked to Varying Effects of Nitrification Inhibitors DCD and DMPP in Two Arable Soils.

The efficacy of nitrification inhibitors (NIs) dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) varies with soil types. Understanding the microbial mechanisms for this variation may lead to better modelling of NI efficacy and therefore on-farm adoption. This study addressed the response patterns of mineral nitrogen, nitrous oxide (N2O) emission, abundances of N-cycling functional guilds and soil microbiota characteristics, in relation to urea application with or without DCD or DMPP in two arable soils (an alkaline and an acid soil). The inhibition of nitrification rate and N2O emission by NI application occurred by suppressing ammonia-oxidizing bacteria (AOB) abundances and increasing the abundances of nosZI-N2O reducers; however, abundances of ammonia-oxidizing archaea (AOA) were also stimulated with NIs-added in these two arable soils. DMPP generally had stronger inhibition efficiency than DCD, and both NIs' addition decreased Nitrobacter, while increased Nitrospira abundance only in alkaline soil. N2O emissions were positively correlated with AOB and negatively correlated with nosZI in both soils and AOA only in acid soil. Moreover, N2O emissions were also positively correlated with nirK-type denitrifiers in alkaline soil, and clade A comammox in acid soil. Amendment with DCD or DMPP altered soil microbiota community structure, but had minor effect on community composition. These results highlight a crucial role of the niche differentiation among canonical ammonia oxidizers (AOA/AOB), Nitrobacter and Nitrospira, as well as nosZI- and nosZII-N2O reducers in determining the varying efficacies of DCD and DMPP in different arable soils.

Soil texture is an easily overlooked factor affecting the temperature sensitivity of N2O emissions.

As a potent greenhouse gas, soil nitrous oxide (N2O) is strongly stimulated by rising temperature, triggering a positive feedback effect of global warming. However, its temperature sensitivity varies greatly among soils with different physical and chemical characteristics, while associated mechanisms remain unknown. Here we performed a meta-analysis of the effect of warming on N2O emission and found distinctions in the response of N2O to temperature increase in soils with different textures. Then, we conducted an incubation experiment on 11 arable soils with varying textures sampled across China. The results show that the temperature sensitivity of N2O emissions was lower as soil texture became more clayey and was consistent with the outcome of meta-analysis. Further analysis was conducted by classifying the soils into clay and loam subgroups. As shown in the clay soil subgroup, N2O emission was significantly correlated with both inorganic nitrogen contents and potential denitrification and nitrification activities. Correlation analysis and partial least square (PLS) path model revealed that temperature mediated N2O emission by regulating nosZ gene abundance indirectly. In loam soils, however, the indirect effect of temperature on N2O production was achieved mainly through nirS gene abundance. Additionally, soil DON content strongly correlated with N2O emission in both subgroups and affected N2O emissions by influencing the abundance of denitrifiers under warming conditions. Our findings suggest that (i) soil texture was an important factor affecting temperature sensitivity of N2O emission and (ii) variable efficacy of warming in soil N2O production might originate from the enriching DON and nitrate content and its different indirect effects on nirS- or nosZ-type denitrifiers.

Core Microbiota in the Rhizosphere of Heavy Metal Accumulators and Its Contribution to Plant Performance.

Persistent microbial symbioses can confer greater fitness to their host under unfavorable conditions, but manipulating such beneficial interactions necessitates a mechanistic understanding of the consistently important microbiomes for the plant. Here, we examined the phylogenetic profiles and plant-beneficial traits of the core microbiota that consistently inhabits the rhizosphere of four divergent Cd hyperaccumulators and an accumulator. We evidenced the existence of a conserved core rhizosphere microbiota in each plant distinct from that in the non-hyperaccumulating plant. Members of Burkholderiaceae and Sphingomonas were the shared cores across hyperaccumulators and accumulators. Several keystone taxa in the rhizosphere networks were part of the core microbiota, the abundance of which was an important predictor of plant Cd accumulation. Furthermore, an inoculation experiment with synthetic communities comprising isolates belonging to the shared cores indicated that core microorganisms could facilitate plant growth and metal tolerance. Using RNA-based stable isotope probing, we discovered that abundant core taxa overlapped with active rhizobacteria utilizing root exudates, implying that the core rhizosphere microbiota assimilating plant-derived carbon may provide benefits to plant growth and host phenotype such as Cd accumulation. Our study suggests common principles underpinning hyperaccumulator-microbiome interactions, where plants consistently interact with a core set of microbes contributing to host fitness and plant performance. These findings lay the foundation for harnessing the persistent root microbiomes to accelerate the restoration of metal-disturbed soils.

The involvement of nitric oxide and ethylene on the formation of endodermal barriers in response to Cd in hyperaccumulator Sedum alfredii.

Nitric oxide (NO) and ethylene are both important signaling molecules which participate in numerous plant development processes and environmental stress resistance. Here, we investigate whether and how NO interacts with ethylene during the development of endodermal barriers that have major consequences for the apoplastic uptake of cadmium (Cd) in the hyperaccumulator Sedum alfredii. In response to Cd, an increased NO accumulation, while a decrease in ethylene production was observed in the roots of S. alfredii. Exogenous supplementation of NO donor SNP (sodium nitroprusside) decreased the ethylene production in roots, while NO scavenger cPTIO (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) had the opposite effect. The exogenous addition of NO affected the ethylene production through regulating the expression of genes related to ethylene synthesis. However, upon exogenous ethylene addition, roots retained their NO accumulation. The abovementioned results suggest that ethylene is downstream of the NO signaling pathway in S. alfredii. Regardless of Cd, addition of SNP promoted the deposition of endodermal barriers via regulating the genes related to Casparian strips deposition and suberization. Correlation analyses indicate that NO positively modifies the formation of endodermal barriers via the NO-ethylene signaling pathway, Cd-induced NO accumulation interferes with the synthesis of ethylene, leading to a deposition of endodermal barriers in S. alfredii.

Positive effects of applying endophytic bacteria in eggplant-Sedum intercropping system on Cd phytoremediation and vegetable production in cadmium polluted greenhouse.

The combination of intercropping and phytoremediation in the remediation of cadmium contaminated soil is an emerging model in recent years, but the results of previous studies are inconsistent. In the field experiment, eggplant was intercropped with hyperaccumulator Sedum alfredii Hance (inoculated or not inoculated with endophytic bacteria) to study the effects of intercropping on vegetable safety production, phytoremediation efficiency of hyperaccumulator and variation of soil available nutrients. The results showed that the intercropping treatment had a negative effect on the growth of eggplant and Sedum, but endophyte SaMR12 alleviated the inhibition of intercropping on plant growth. Intercropping treatment increases the Cd concentration in edible part of eggplant to 1.34 mg/kg compared with eggplant monoculture (1.19 mg/kg). While the application of SaMR12 reduces the Cd concentration of eggplant fruit to 0.95 mg/kg and significantly promotes the Cd uptake by Sedum. What's more surprising is that compared with eggplant monocropping, the content of soil available nitrogen, phosphorus and potassium in the treatment of intercropping with inoculated Sedum increased significantly. And according to the correlation analysis of various indexes of plants and soil, the Cd content of eggplant is negatively correlated with the available phosphorus and potassium in the soil, while the Cd content of Sedum is positively correlated with it, which suggested that the application of phosphorus and potassium fertilizers in this experimental site was beneficial to reduce Cd content in eggplant and improve Cd phytoextraction of Sedum. Therefore, in the daily production of moderately Cd-contaminated soil, intercropping eggplant with Sedum inoculated with endophytic bacteria is an excellent Phytoextraction Coupled with Agro-safe-production (PCA) pattern.

Integrated glycolysis and pyrolysis process for multiple utilization and cadmium collection of hyperaccumulator Sedum alfredii.

Phytoremediation is a cost-effective and environmentally-friendly method to treat cadmium (Cd) contaminated soils, however, there is still a lack of safe disposal methods of harvested hyperaccumulators. In this study, by integrating glycolysis and pyrolysis, we investigated the possibility of bioproduct production and Cd collection from the hyperaccumulator Sedum alfredii. By means of acid-alkali pretreatment, the degree of cellulose polymerization was reduced by 36.24% while the surface accessibility was increased by 115.80%, resulting in a bioethanol yield of 9.29%. Meanwhile, 99.22% of total Cd of biomass could be reclaimed by collecting H2SO4-pretreatment waste. The saccharification residue was subsequently modified by NaOH-pretreatment-filtrate and converted into biochar at 500 °C which possessed a maximum Cd2+ sorption capacity of 60.52 mg g-1 based on the Langmuir model. Furthermore, sustainability analysis indicated that the economic input of this process is acceptable when considering its good environmental benefits. Taken together, our study provides a strategy for simultaneous bioethanol and biochar production during Cd collection from the hyperaccumulator S. alfredii, which could be a promising alternative for the suitable treatment of metal-enriched plants.

The Cd phytoextraction potential of hyperaccumulator Sedum alfredii-oilseed rape intercropping system under different soil types and comprehensive benefits evaluation under field conditions.

Soil trace elements (TEs) contamination has become a worldwide problem in arable lands and poses great risk to human health via food chain. Intercropping of hyperaccumulator and cash crops is now proposed as a promising alternative phytoremediation technique to address the issue. However, the effect of intercropping in different soil types and field-scale benefits evaluation are rarely reported. A greenhouse pot experiment and a field trial were therefore designed to explore the effects of intercropping Sedum alfredii (hyperaccumulative population) and oilseed rape on Cd phytoextraction potential, Cd transport and crop production, as well as establishing a feasible assessment framework on the basis of benefits evaluation in contaminated soils. Compared with oilseed rape monoculture, intercropping with S. alfredii significantly and consistently increased biomass, seed yield and Cd accumulation in oilseed rape in five typical soil types. Accumulations of Cd varied with soil types, ranging from 22.8 to 4000 µg pot-1. Stepwise multiple linear regression analysis (SMLRA) showed Cd concentrations in plants were related to available phosphorus (AP), pH, soil organic matter (OM), available potassium (AK), silt and sand; R2 values varied from 0.834 to 0.994 (P < 0.05). A field trial also verified that intercropping could significantly enhance Cd phytoextraction. The highest index for comprehensive benefits evaluation was 0.61 observed in the S. alfredii and oilseed rape intercropping system. This system presented higher Cd phytoextraction potential and comprehensive benefits index whilst allowing ongoing agricultural activities in slightly and moderately Cd-contaminated soils. These results provide a possible technical approach for phytoremediation practice and give new insights into theoretical reference for development of Cd phytoextraction and benefits evaluation.

Loss of organic carbon in suburban soil upon urbanization of Chengdu megacity, China.

Urbanization is progressing rapidly. It can affect soils ecosystem services directly through land management and indirectly through changes in the socioeconomic environment, which eventually leads to an increase in emissions of greenhouse gases. Soil carbon (C) sequestration plays an important role in offsetting the anthropogenic C emissions. However, there is limited knowledge of how urbanization affects the soil C especially that in suburban. In this study, we studied changes in easily oxidizable organic C (EOC) and total organic C (TOC) of suburban soils (0-100 cm) in the rapid urbanising megacity Chengdu, China. The EOC stock and TOC stock decreased from the outer-suburb to the inner-suburb by 17.8-28.2% and 5.4-13.5%, respectively; particularly, the inner-suburb EOC decreased by 31.4-38.6% during the past 10 years. The quotient of EOC/TOC in the soil profile, reflecting the stability of soil C, declined from the outer-suburb (0.78) to the inner-suburb (0.20). Factors that influenced the EOC and TOC included the changes in economics (economic density, industrialization), farmland (cultivated area, farmland structure), urbanization (city size, population growth) and traffic flow. Among which, economic density growth was the primarily driver of the loss in TOC, explaining 31.6% of the variation in soil surface TOC and 16.0% of the variation in subsoil TOC; changes in farmland and urban expansion were the main factors contributing to the loss of subsoil EOC, with 40.4% explanatory ability. In addition, traffic flow also has contribution to the subsoil EOC loss. We concluded that the increasing soil C loss with decreasing distance from the city centre has a continuous contribution to C emission, and the C loss will persist until the suburbs are fully urbanized. The large losses of EOC and TOC caused by urbanization, and their contribution to global warming, necessitate their consideration in future appraisals of climate change and urban planning projects.

Exposure of cerium oxide nanoparticles to the hyperaccumulator Sedum alfredii decreases the uptake of cadmium via the apoplastic pathway.

Cadmium (Cd) is harmful to the environment and threatens human health. With the increasing use of cerium oxide nanoparticles (CeO2NPs) in extensive industries, investigating the combination of CeO2NPs and plants has attracted research interests for phytoremediation. Here, we explored the effects of CeO2NPs on Cd uptake, transport and the consequent Cd accumulation in Sedum alfredii. Exposure of 50 or 500 mg L-1 CeO2NPs alone had no apparent damaging effects on plant growth. However, upon Cd condition, the consistent CeO2NPs decreased Cd concentrations in the roots and shoots by up to 37%. Furthermore, the application of a metabolic inhibitor revealed that CeO2NPs mainly decreased the Cd uptake in roots by the apoplastic pathway. Simultaneously, CeO2NPs accelerated the development of Casparian strips (CSs) and suberin, which was further proven by the elevated expression levels of genes associated with their formation, SaCASP, SaGPAT5, SaKCS20 and SaCYP86A1. Compared to CeO2NPs added alone, the concurrent Cd decreased the Ce contents in the roots and altered its translocation from root to shoot. Taken together, both CeO2NPs and Cd influence the interactional uptake of both chemicals in roots of S. alfredii mainly via the apoplastic pathway which is primarily regulated by the development of CSs and suberin.

The influence of elevated CO2 on bacterial community structure and its co-occurrence network in soils polluted with Cr2O3 nanoparticles.

Elevated CO2 (eCO2) and nanoparticles release are considered among the most noteworthy global concerns as they may impose negative effects on human health and ecosystem functioning. A mechanistic understanding of their combined impacts on soil microbiota is essential due to the profound eCO2 effect on soil biogeochemical processes. In this study, the impacts of Cr2O3 nanoparticles (nano-Cr2O3) on the activity, structure and co-occurrence networks of bacterial communities under ambient and eCO2 were compared between a clay loam and a sandy loam soil. We showed that eCO2 substantially mitigated nano-Cr2O3 toxicity, with microbial biomass, enzyme activity and bacterial alpha-diversity in clay loam soil were much higher than those in sandy loam soil. Nano-Cr2O3 addition caused an increase in alpha-diversity except for clay loam soil samples under eCO2. 16S rRNA gene profiling data found eCO2 remarkably reduced community divergences induced by nano-Cr2O3 more efficiently in clay loam soil (P < 0.05). Network analyses revealed more complex co-occurrence network architectures in clay loam soil than in sandy loam soil, however, nano-Cr2O3 decreased but eCO2 increased modularity and network complexity. Rising CO2 favoured the growth of oligotrophic (Acidobacteriaceae, Bryobacteraceae) rather than the copiotrophic bacteria (Sphingomonadaceae, Caulobacteraceae, Bacteroidaceae), which may contribute to community recovery and increase available carbon utilization efficiency. Our results suggested that the degree to which eCO2 mitigates nano-Cr2O3 toxicity is soil dependent, which could be related to the variation in clay and organic matter content, resilience of the resistant bacterial taxa, and microbial network complexity in distinct soils.