Excessive iron deposition in root apoplast is involved in growth arrest of roots in response to low pH.

The rhizotoxicity of protons (H+) in acidic soils is a fundamental constraint that results in serious yield losses. However, the mechanisms underlying H+-mediated inhibition of root growth are poorly understood. In this study, we revealed that H+-induced root growth inhibition in Arabidopsis depends considerably on excessive iron deposition in the root apoplast. Reducing such aberrant iron deposition by decreasing the iron supply or disrupting the ferroxidases LOW PHOSPHATE ROOT 1 (LPR) and LPR2 attenuates the inhibitory effect of H+ on primary root growth efficiently. Further analysis showed that excessive iron deposition triggers a burst of highly reactive oxygen species, consequently impairing normal root development. Our study uncovered a valuable strategy for improving the ability of plants to tolerate H+ toxicity by manipulating iron availability.

[Simultaneous Immobilization of Cadmium and Arsenic in Paddy Soils with Novel Fe-Mn Combined Graphene Oxide].

Novel Fe-Mn combined graphene oxide （GO-FM） material was produced and tested for its efficacy in remediating agricultural soil co-contaminated by Cd and As. In a 60-day soil incubation experiment， the remediation mechanism and immobilization effects of GO and GO-FM at different addition ratios （0.1%， 0.2%， and 0.3%） were investigated in Shangyu and Foshan soils， which had varying physicochemical properties and contamination degrees. The dynamic changes in pH， DOC concentration， bioavailable Cd and As content， and morphology of Cd and As were explored to determine the remediation efficacy of the materials. The results demonstrated that compared with that in the blank control， GO-FM increased the pH in Shangyu soil but decreased the pH in Foshan soil. After culture， both GO and GO-FM increased the soil DOC content. GO-FM decreased the soluble Cd concentration by 5.08%-19.19% and the bioavailability of Cd by 36.57%-42.8% in Foshan soil， and the main immobilization mechanism was electrostatic adsorption， complexation， and hydroxylated metal ion formation. The immobilization ability of GO-FM on Cd was lower than that of Foshan soil due to the influence of electrostatic repulsion in Shangyu acidic soil. However， with the increase in the amount of GO-FM， the trend of increasing the bioavailability of Cd by graphene oxide was inhibited. The addition of 0.2% and 0.3% GO-FM decreased the bioavailability of Cd by 6.45%-13.56% in Shangyu soil. Additionally， GO-FM decreased the bioavailability of As in Shangyu soil and Foshan soil by 4.34%-9.15% and 0.87%-5.71%， respectively. This was due to the immobilization mechanism of oxidation of As by manganese oxides and inner surface chelate between As and the surface hydroxyl group of iron oxides. In summary， the immobilization effect of GO-FM on Cd in Foshan soil was better than that in Shangyu soil， and the immobilization effect of GO-FM on As in Shangyu soil was better than that in Foshan soil， which can provide a theoretical basis and reference for the prevention and control of Cd and As co-contamination in different types of soil.

[Using Biochar and Iron-calcium Material to Remediate Paddy Soil Contaminated by Cadmium and Arsenic].

In this study, iron-calcium material (FC) and hickory-cattail biochar (BC) were applied to prepare composite material (BF), which was used to repair the combined pollution of cadmium and arsenic in paddy soil to reduce the content of cadmium (Cd) and arsenic (As) in rice grain. Soil pore water, rhizosphere soil, bulk soil, rice plants, and root iron plaque samples were collected during the growth period of rice in a pot experiment to explore the effects and mechanism of FC, BC, and BF on the bioavailability of Cd and As in paddy soil and their contents in plants. The results showed that biochar could significantly (P < 0.05) increase the pH value of bulk soil (0.55-0.66 units) and rhizosphere soil (0.28-0.36 units) and elevate the soil dissolved organic carbon (DOC) content. FC material could significantly (P < 0.05) reduce the pH of bulk soil (0.14-0.27 units) and rhizosphere soil (0.38-0.41 units), as well as the soil DOC content. Iron-calcium materials and composite could simultaneously reduce the contents of available Cd and As in soil pore water, rhizosphere soil, and bulk soil, whereas biochar could reduce the content of Cd but increase the content of As. Among them, a 1% addition of composite had the best effect. The available Cd and As in soil decreased by 41.8%-48.2% and 6.1%-10.1%, respectively. Biochar, iron-calcium materials, and composites improved plant biomass (dry weight of root, stem, leaf, and grain). For example, the dry weights of rice grains under these treatments were higher (48.5%-184.0%) than that of CK, as was the root iron plaque content (7.5%-13.6%). Compared with that in the CK, biochar could effectively reduce the Cd content in rice grain by 21.0%-26.1%. Iron-calcium material and composite could simultaneously reduce the Cd and As contents in rice grain. Among them, the BF treatment had the best effect on the reduction of Cd and As in rice grain, with a decrease of 36.9%-42.0% and 40.4%-44.4%, respectively. The Cd and As contents in rice grain were lower than the national standard values (GB 2762-2017).

Microplastic exposure inhibits nitrate uptake and assimilation in wheat plants.

Microplastic (MP) contamination in soil severely impairs plant growth. However, mechanisms underlying the effects of MPs on plant nutrient uptake remain largely unknown. In this study, we revealed that NO3- content was significantly decreased in shoots and roots of wheat plants exposed to high concentrations (50-100 mg L-1) of MPs (1 µm and 0.1 µm; type: polystyrene) in the hydroponic solution. Isotope labeling experiments demonstrated that MP exposure led to a significant inhibition of NO3- uptake in wheat roots. Further analysis indicated that the presence of MPs markedly inhibited root growth and caused oxidative damage to the roots. Additionally, superoxide dismutase and peroxidase activities in wheat roots decreased under all MP treatments, whereas catalase and ascorbate peroxidase activities significantly increased under the 100 mg L-1 MP treatment. The transcription levels of most nitrate transporters (NRTs) in roots were significantly downregulated by MP exposure. Furthermore, exposure to MPs distinctly suppressed the activity of nitrate reductase (NR) and nitrite reductase (NiR), as well as the expression levels of their coding genes in wheat shoots. These findings indicate that a decline in root uptake area and root vitality, as well as in the expression of NRTs, NR, and NiR genes caused by MP exposure may have adverse effects on NO3- uptake and assimilation, consequently impairing normal growth of plants.

[Novel Insight into the Adsorption Mechanism of Fe-Mn Oxide-Microbe Combined Biochar for Cd(â ¡) and As(â ¢)].

A Fe-Mn oxide-microbe combined biochar (FM-DB) was prepared to simultaneously remove Cd(Ⅱ) and As(Ⅲ) contamination in an aqueous system. In the FM-DB, the best ratio of Fe-Mn oxide (FMBO) and carya cathayensis shell biochar (CCSB) was 3%+3%. The material had good acid resistance, mechanical strength, and mass transfer performance, and the maximum removal rates for Cd(Ⅱ) and As(Ⅲ) in the binary system were 77.29% and 99.94%, respectively. Characterization confirmed that the FM-DB was successfully prepared and had a rich functional group structure. The single-factor adsorption test results for Cd(Ⅱ) and As(Ⅲ) showed that the composite material had a certain adsorption capacity affected by initial pH, equilibration time, and initial concentration for Cd(Ⅱ) and As(Ⅲ) under different conditions. The adsorption isotherm and kinetic data indicated the adsorption equilibrium time for Cd(Ⅱ) and As(Ⅲ) was 3.5 h and 8 h, and the maximum capacity was 59.27 mg·g-1and 84.73 mg·g-1, respectively. The adsorption of Cd(Ⅱ) and As(Ⅲ) was mainly affected by the electron exchange, electron sharing, and complexation on the surface of the material. The whole adsorption process was a combination of single-layer adsorption and multi-layer adsorption on an uneven surface. The adsorption process was a multi-step process, including outer surface diffusion and inner particle diffusion. In addition, comparing the removal rate of composite materials in the single-component system and the binary system, a mutual promotion of adsorption between Cd(Ⅱ) and As(Ⅲ) was found under the binary system. In conclusion, oxide-microbe combined biochar could be an efficient adsorption material and was suitable for the remediation of aqueous system pollution caused by Cd(Ⅱ) and As(Ⅲ).

[Spatial Distribution Characteristics and Risk Assessment of Cadmium Pollution in Soil-crops system of an E-waste Dismantling Area].

With the rapid development of electronic technology, soil heavy metal contamination caused by electronic waste dismantling activities has attracted the attention of many researchers. To investigate the contamination status and spatial distribution of Cd in soil-crop systems around an e-waste dismantling area, 171 pairs of soil and crop samples were collected for analysis. The concentrations of cadmium in root vegetable soil, leaf vegetable soil, solanaceous vegetable soil, and orchard soil were (1.292±0.647), (1.010±0.201), (0.921±0.125), and (0.861±0.135) mg·kg-1, respectively. The average values of cadmium in these four soil types were 10.0, 7.8, 7.1, and 6.3 times the background values of soil Cd in Zhejiang Province, respectively, and 4.31, 3.4, 3.07, and 2.72 times the risk screening values for soil contamination of agricultural land, clearly indicating cadmium accumulation in the soil. However, only a small percentage of crops contained cadmium levels that exceeded food safety limits. Moreover, different types of crops showed different capacities for cadmium enrichment and can be ranked accordingly: leaf vegetables > root vegetables > solanaceous vegetables > fruits. The single factor pollution index and the potential ecological risk assessment revealed severe Cd contamination in the study area, with a high potential ecological risk. Cadmium exposure posed a higher health risk for children than for adults. However, the single heavy metal cadmium pollution index does not indicate a threat to local residents at this time. Moran's I index and kriging interpolation results revealed that Cd has significant spatial autocorrelation, with high values mainly concentrating around the e-waste dismantling area, indicating a significant correlation with e-waste dismantling activities.

[Simultaneous Immobilization of Arsenic, Lead, and Cadmium in Paddy Soils Using Two Iron-based Materials].

Two iron-based materials, Fe-Ca composite (FeCa) and Fe-Mn binary oxide (FMBO), were applied to immobilize As, Pb, and Cd in heavy metal contaminated paddy soils. Seven kinds of paddy soil (tidal soil) contaminated by arsenic, lead and cadmium were collected from Shangyu, Shaoxing (SY), Foshan, Guangdong (FS), Shaoguan, Guangdong (SG), LiuYang, Hunan (LY), Ganzhou, Jiangxi (GZ), Dushan, Guizhou (DS), and Ma'anshan, Anhui (MAS). The effects of iron-based materials on the dynamic changes of As, Pb, and Cd concentration in soil solution, the stabilization efficacy of available As, Pb, and Cd in soil, and the effects of soil types and properties on stabilization efficacy were studied through soil incubation experiment. The results showed that the content of soil dissolved As, Pb, and Cd were lower in iron-based material treatments than in control throughout the incubation. The addition of two iron-based materials significantly reduced the availability of Cd, Pb, and As. Moreover, the stabilization efficiency of FeCa for As was higher than FMBO, but no significant difference was found in the stabilization efficiency of Pb and Cd between two materials. The stabilization efficiency of As, Pb, and Cd in FeCa treatments could be ordered as GZ > SG > DS and MAS; FS>SY, LY, and SG>MAS; SY, GZ, and DS>MAS, respectively. While the stabilization efficiency for As, Pb, and Cd in FMBO could be ordered as SY, LY, and GZ > DS > FS; FS > GZ > SY; DS > LY > MAS, respectively. In addition, the statistical results showed that the stabilization efficiencies of various soils under the treatment of iron-based materials were significantly correlated with sand content (negatively correlated for As), soil pH (positively correlated for Pb), and clay content (negatively correlated for Cd). In conclusion, the two iron-based materials evaluated in this study may be effective stabilization agents for remediating different types of arsenic-, lead-, and cadmium-contaminated soils.

NRT1.1 Dual-Affinity Nitrate Transport/Signalling and its Roles in Plant Abiotic Stress Resistance.

NRT1.1 is the first nitrate transport protein cloned in plants and has both high- and low-affinity functions. It imports and senses nitrate, which is modulated by the phosphorylation on Thr101 (T101). Structural studies have revealed that the phosphorylation of T101 either induces dimer decoupling or increases structural flexibility within the membrane, thereby switching the NRT1.1 protein from a low- to high-affinity state. Further studies on the adaptive regulation of NRT1.1 in fluctuating nitrate conditions have shown that, at low nitrate concentrations, nitrate binding only at the high-affinity monomer initiates NRT1.1 dimer decoupling and priming of the T101 site for phosphorylation activated by CIPK23, which functions as a high-affinity nitrate transceptor. However, nitrate binding in both monomers retains the unmodified NRT1.1, maintaining the low-affinity mode. This NRT1.1-mediated nitrate signalling and transport may provide a key to improving the efficiency of plant nitrogen use. However, recent studies have revealed that NRT1.1 is extensively involved in plant tolerance of several adverse environmental conditions. In this context, we summarise the recent progress in the molecular mechanisms of NRT1.1 dual-affinity nitrate transport/signalling and focus on its expected and unexpected roles in plant abiotic stress resistance and their regulation processes.

[Spatial Variation of Soil Heavy Metals in Lin'an City and Its Potential Risk Evaluation].

Urban soil is an important part of the urban ecosystem, which is strongly correlated with human health and life quality. In this study, Lin'an city was chosen as a typical small city to study the spatial variation and distribution of heavy metals in urban soils and their pollution characteristics using multivariate analysis, geostatistics, and GIS techniques. A total of 62 soil samples were collected from the study areas. The results indicated that the average concentrations of soil Mn, Cu, Zn, Pb, Cr, and Cd were 439.42, 42.23, 196.80, 62.55, 63.65, and 0.22 mg·kg-1, respectively. Compared with the background values and the environmental quality standards, these heavy metals were accumulated in urban soils to some extent. Almost 80% of the study area was polluted by heavy metals. The single potential ecological risk index of heavy metals indicated that Pb had the highest ecological risk. The pH and most of the heavy metals had strong correlations, and there were strong correlations among the heavy metals. The principle component analysis (PCA) showed that Pb, Zn, and Cu had the same pollution source, which was related to vehicle exhausts; Mn and Cr were mainly from the parent material; and Cd was from the emissions of manufacturing plants. The spatial structure and distribution of heavy metals and their corresponding available fractions had strong spatial autocorrelation with all of the C0/(C0+C)<50%. Their spatial patterns were influenced by human activities.

[Spatial Variation of Heavy Metals in Soils and Its Ecological Risk Evaluation in a Typical Carya cathayensis Production Area].

In recent years, the problem of soil pollution has become more and more serious. The problem of soil heavy metal pollution and its related human health risks has become a hot spot at home and abroad. Carya cathayensis is a unique high-grade woody nut and oil tree from China, and there are few reports on heavy metal pollution in Carya cathayensis plantation soils. Therefore, in order to study the spatial variability of heavy metals and the risk of pollution in Carya cathayensis soil and to promote the sustainable development of the Carya cathayensis industry, Lin'an, a typical Carya cathayensis plantation area, was selected for this study. A total of 188 soil samples were collected from the study area. We systematically studied the spatial heterogeneity of soil heavy metal content in the study area based on GIS technology, geostatistics, Moran's I, and other spatial analysis methods. The single factor pollution index method, the Nemerow comprehensive pollution index method, and the potential ecological risk assessment method were used to evaluate the heavy metal pollution in the study area. The results indicated that the mean content of soil cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and chromium (Cr) were 0.37, 40.76, 87.61, 30.10, 28.33, 56.57 mg·kg-1, respectively. The average values of Cd and Cu were 1.33 and 2.87 times of the background values, respectively, and the average content of other heavy metals did not exceed the background values. The results of the single factor Nemerow pollution index and potential ecological risk assessment methods showed that heavy metals in the study area exceeded the soil background values in some samples, and the second grade standard of soil environmental quality was exceed for Cd, Cu, Zn, Pb, and Ni in 31.38%, 31.38%, 2.65%, 0.53%, and 17.02% of the samples, respectively. This indicated that the soils in the study area had different accumulation characteristics for Cd, Cu, Zn, Pb, Ni, and Cr, and the local soil had reached pollution levels for Cd, Cu, Zn, Pb, and Ni. Among them, Cd was the most serious, reaching the degree of strong ecological damage, followed by Cu. In general, the heavy metal contents indicated a moderate degree of ecological damage. Based on the analysis of the semi-variance function, the Cd, Cu, and Ni in the soil were best fit with exponential models, the Zn and Pb were better fit with the Gaussian model, and Cr was consistent with the spherical model. Cd, Cu, Pb, Ni, and Cr had the strong spatial autocorrelation, with Nugget/Sill ratios of 12.1%, 4.6%, 14.9%, 2.6%, and 11.2%, respectively, while the Nugget/Sill ratio of Zn was 48.8%, indicating a medium spatial autocorrelation. Moran's I and Kriging interpolation results found that the heavy metals Cd, Cu, Zn, Pb, Ni, and Cr all had obvious spatial distribution patterns and local spatial aggregation phenomena. The high values of heavy metals in soils were mainly found in Taiyang, Daoshi, Qingliangfeng, Heqiao, and Tuankou, and the probability of the risk for contamination by Cd and Cu was higher in the study area. The high values of Cd, Cu, Zn, Ni, and Cr were mainly related to mining, while Pb was closely related to the application of potassium.

[Spatial Variation of Soil Heavy Metals in an E-waste Dismantling Area and Their Distribution Characteristics].

A total of 90 soil samples were collected from the study area. The spatial variation of soil heavy metals and their spatial distribution characteristics were studied. The results indicated that the mean soil concentrations of five heavy metals including Cd, Cu, Zn, Pb and Ni were 0.38, 35.13, 121.38, 35.40 and 28.13 mg·kg-1, respectively. Compared with the background values in Zhejiang, the heavy metals were enriched in paddy soils of the study area. Part of study area was seriously contaminated by heavy metals. For the soil Cd, it had obvious contamination characteristics with a high Pi Avevalue (>1). The Cd, and Pb concentrations in paddy soil had strong coefficients of variance (C.V.): 121.05% and 109.38%, respectively. Soil pH and organic matter (SOM) had significant correlations with most of the total heavy metals and their available fractions in soils. The total heavy metals and their available fractions also had strong correlations, such as total Cd and available Cd in soils. Geostatistics and the Local Moran's Ⅰ were used to identify the contaminated hotspots of these five metals. It was found out that the high soil Cd, Cu, Zn, Pb were located in Daxi and Zeguo towns, which could be attributed to E-waste dismantling and other anthropogenic activities. Soil Ni was mainly influenced by the parent material. The heavy metals in soils may pose a potential threat to local ecosystem and human health.

[Changes in soil organic carbon and soil microbial functional diversity of Carya cathayensis plantations under intensive managements].

The change characteristics of soil organic carbon and microbial function diversity in Chinese hickory Carya cathayensis stands with different intensive-management durations (5, 10, 15 and 20 years) were studied. The results showed that soil total organic carbon (TOC), microbial biomass carbon (MBC), water-soluble organic carbon (WSOC) decreased significantly, while the stability of soil C pool increased significantly after the conversion from evergreen and deciduous broadleaf forest to intensively-managed forest (IMF). TOC, MBC and WSOC in the hickory forest soil decreased by 28.4%, 34.1% and 53.3% with 5-year intensive management, and by 38.6%, 48.9% and 64.1% with 20-year intensive management, respectively. The proportions of carboxyl C, phenolic C and aromatic C in the hickory forest soil all increased significantly, and the aromaticity of soil organic C increased by 23.0%. Soil microbial functional diversity decreased greatly af- ter intensive management of Chinese hickory forest. Significant differences in average well color development (AWCD) were found between the 0- and 5-year treatments and the 10-, 15- and 20- year treatments. The microbial diversity indexes (H) and evenness indexes (E) in the 0- and 5-year treatments were much greater than in the 10- and 20-year treatments. Correlation analysis showed that there were significant correlations among soil TOC, WSOC, MBC, AWCD, H and E.

[Assessment of toxicity of heavy metal contaminated soils by toxicity characteristic leaching procedure].

The contents of heavy metals (Cu, Zn, Pb and Cd) in soils from a lead-zinc mine in Shangyu, Zhejiang Province, China, were analyzed and their toxicity was assessed by toxicity characteristic leaching procedure (TCLP), which was developed by US EPA. The TCLP method is a currently recognized international method for evaluation of heavy metal pollution in soils. The available levels of Cu, Zn, Pb and Cd were 8.2-36 mg x kg(-1), 23-143 mg x kg(-1), 6.4-1367 mg x kg(-1) and 0.41-2.2 mg x kg(-1), respectively, while the international standard were 15 mg x kg(-1), 25 mg x kg(-1), 5 mg x kg(-1) and 0.5 mg x kg(-1), respectively. The results show that soils around the mine are polluted with heavy metals Cu, Zn, Pb and Cd, especially polluted by Zn and Pb, followed by Cd and Cu. Moreover, the heavy metals in the soils extracted by TCLP indicate that fluid 2 is more effective than fluid 1 in extracting the heavy metals from the polluted soils and there is a positive correlation between fluid 1 and fluid 2. The contents of available heavy metals by TCLP are correlated with contents of total heavy metals.