Hyperaccumulators are a group of specialized plants that absorb large amounts of heavy metals and store most of them in their aboveground parts. These plants are rich in organic ligands, such as nicotianamine and histidine, which can combine with metals to form metal-ligand complexes. At present, the studies on nickel and zinc organic ligands in plants are relatively sufficient. Therefore, this paper focuses on the interaction between organic ligands and heavy metals during root transport and detoxification, xylem transport and leaf detoxification processes, the molecular mechanism of organic ligand synthesis in hyperaccumulators, as well as methods for detection of organic ligands and metal complexes. To sum up, organic ligands may promote the migration of Ni and Zn in the symplasts of hyperaccumulators and alleviate the cytotoxicity of excess Ni and Zn. In the process of xylem transport, nickel and zinc mainly occur by hydrated ions, but the role of organic ligands is relatively weak in this process. Nickel and zinc mainly combine with organic acid for leaf detoxification. Since most of the findings come from a limited number of hyperaccumulators and organic ligands, it is necessary to combine metabonomics and transcriptomics to study the characteristics and molecular mechanisms about detoxification of organic ligands in more species of hyperaccumulators in the future, so as to provide theoretical basis for clarifying the relevant mechanisms of selective hyperaccumulation of heavy metals in plants and for the application of hyperaccumulators in phytoextraction.

Under the goals of carbon peaking and carbon neutrality, stimulating the endogenous motivation of farmers to participate in low-carbon production plays an important element to improve the mechanism of agricultural ecological environment and promote rural revitalization in the new period. This paper constructs a theoretical logical framework of "grassroots organizations embedding-rural sense of belonging-farmers' low-carbon production behaviour". Based on the survey data of micro-farmers, the Ordered Logit regression model is used to test the influence of grassroots organizations embedding on farmers' low-carbon production behaviour, and the mediating effect of rural sense of belonging in the influence of grassroots organizations embedding on farmers' low-carbon production behaviour is tested using the mediating effect model. The results show that the depth and breadth of embedding of grassroots organizations can significantly contribute to farmers' participation in low-carbon production, and that the relationship remains significant after adjusting for possible endogeneity issues in the model. Following robustness tests of the baseline regressions by three strategies:the substitution model estimation method, the replacement core explanatory variables method and the random sampling 2/3 sample method, the effect of grassroots organizations embedding on farmers' low-carbon production behaviour remains unchanged. There is a significant mediating effect of rural sense of belonging on the influence of grassroots embedding on low-carbon production behaviour, with both the depth and breadth of embedding significantly increasing the probability of farmers' participation in low-carbon production by enhancing their rural sense of belonging. Therefore, this paper presents policy recommendations to stimulate the willingness of grassroots organizations to embed low-carbon agricultural production, develop innovative modes of promoting low-carbon agricultural production, and enhance the integration of low-carbon agricultural production with people's well-being.

To explore the pollution characteristics, sources, and source-specific health risks of PM_2.5-bound heavy metals (HMs) during winter in the north suburb of Nanjing, daily PM_2.5 filter samples were collected during January and February 2021. The distribution characteristics and chemical speciation of 11 HMs (Al, V, Cr, Mn, Co, Cu, As, Sr, Cd, Ba and Pb) in PM_2.5 were determined by BCR extraction and ICP-OES. Positive matrix factorization (PMF), as well as the modified health risk assessment method was used to analyze the source-specific health risks of HMs, which could find out the major health abuser. The influence of the regional transmission was evaluated using PMF, the concentration-weighted trajectory (CWT) method and Hybrid Single Particle Lagrangian Integrated Trajectories (HYSPLIT), respectively. The results showed that the average daily concentration of PM_2.5 was (99.0±18.3) μg·m^-3, and 92.3% of the days in the sampling period exceeded the daily average limit of the National Ambient Air Quality Standard (GB 3095-2012). The total contents of HMs was (1 999.0±307.2) ng·m^-3, while the average value of As and Cd were (7.0±3.5) and (22.0±14.0) ng·m^-3 ,respectively,both higher than the GB 3095-2012 limit value. Most of the studied HMs (V, Cr, Mn, As, Sr, Cd, Ba) were mainly concentrated in acid-soluble fraction (F1) with high bioavailability, a relatively high percentage of Co, Cu and Pb were present in reducible fraction (F2). Al was mostly concentrated in residual fraction (F4) with low bioavailability. Dust sources (31.4%), coal sources (17.7%) and the mixed sources of traffic and industry (50.9%) were the main sources of metal elements. Non-cancer risks of heavy metals were negligible with values under 1, and Cr, Co, As, Cd posed potential cancer risk to child and adults with values between 10^-6 and 10^-4. It could not be ignored that the impact of the mixed sources of industrial and traffic and regional transmission from Xinyang city of Henan Province and eastern Anhui Province on health risks in the northern suburbs of Nanjing. Therefore, it is not only necessary to strengthen the control of local industrial emissions, but also to pay close attention to the impact of regional transmission.

Ecological conservation redlines are baselines and lifelines to guarantee national and local ecological safety. Rapid urbanization development has led to anthropogenic disturbance expansion and urban population aggregation. Highly intensive anthropogenic activities have posed great threats to habitats and wildlife in the ecological conservation redlines. Taking the ecological conservation redline of Nanjing City as the research area in this study, the risk transfer network "human activity (hazardousness)-risk stressor (joint exposure)-ecological conservation redline (vulnerability)-anthropogenic disturbance risk" based on the Bayesian network was proposed. After that, the anthropogenic disturbance risk, which was caused by risk sources including construction land, cropland, transport land, and mining areas, was probabilistically evaluated. The following results were obtained: (1) The anthropogenic disturbance risk level was the highest in the red-line regions of Jianye District, corresponding to approximately 3.13% of high risk; (2) The hazardousness level under human activities was relatively higher in the built-up areas (especially in Qinhuai, Yuhuatai, and Gulou districts) than in the suburbs of Nanjing City, while the vulnerability level was relatively higher in the suburbs (especially in Gaochun and Liuhe districts) than in the built-up areas of Nanjing City; (3) According to the sensitivity analysis, ecological management of Jianye District can be improved by the supervision of human activities within red-line regions, important wetlands management and protection, and ecological environment monitoring capacity enhancement. This research may provide technical support for the supervision of human activity and risk management in the ecological conservation redlines.

Michelia martinii is an arboreal tree belonging to the genus Michelia of Magnolia family. It has high ornamental value and is an excellent tree for spices and wood. However, its wild resources were not well preserved, and it was listed as one of the rare and endangered plants of national grade Ⅱ (1999). Now its protection level is Near Threatened (NT). The prediction of the effects of climate change on its distribution could provide a scientific basis and reference for the conservation and sustainable utilization of this wild resource. In this study, ArcGIS 10.4 and MaxEnt 3.4.1 model were used to analyze the potential distribution of Michelia martinii across the country, which was compared with Bioclim and Domain models of DIVA-GIS 7.5 software. The MaxEnt model with the best prediction results was then selected, and the distribution of suitable areas under four climate scenarios (RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5) in the 2050s and 2070s was predicted. The results show that the MaxEnt model could predict the potential habitat distribution accurately, and the AUC (area under ROC Curve) value of the ROC (receiver operating characteristic) training set was 0.977. Precipitation of driest month, altitude, monthly mean temperature diurnal range, and annual precipitation were the main environmental factors affecting the distribution of Michelia martinii, and the contribution rates were 43.8%, 20.7%, 15.2%, 8.8%, respectively. The high, middle and low suitable growth regions of Michelia martinii spread around Guizhou Province, covering a total area of about 5.7×10⁵ km². In the 2050s and 2070s, the distribution pattern of suitable growth regions will remain unchanged. In the 2050s, except for scenario RCP 8.5, the area of low and medium suitable areas and the total area of suitable areas of Michelia martinii under the other three scenarios will be increased. In the 2070s, the areas of medium and high fitness areas and total suitable areas of Michelia martinii will be decreased under all the four scenarios. In the future, global warming will significantly reduce the high suitable area of Michelia martinii. Under most scenarios in the future, the distribution centroid of Michelia martinii will have a trend moving to the northeast. The difficulty of protecting Michelia martinii was that its habitats are isolated and far away from each other, which intensifies the possibility of extinction. In the future, the protection of endangered resources of Michelia martinii should be combined with the prediction results of geographical distribution, from the aspects of the investigation of wild resources, ex situ protection of field return, establishment of protected areas in situ, research on reproduction and cultivation techniques, etc.

The key to the successful invasion of Spartina alterniflora lies in its ability to grow, reproduce and adaptability to the environment. The biomass of S. alterniflora is an important embodiment of its invasion ability. Taking the unmanned aerial vehicle (UAV) remote sensing image as the data source, this study estimated the above-ground biomass of S. alterniflora through the model which was composed by vegetation coverage and plant height. The results indicate that in the typical area of Tiaozini, the biomass of S. alterniflora is between 0 and 9.13 kg·m^-2 and the average biomass is 0.73 kg·m^-2 with 75.13% of S. alterniflora biomass being less than 0.73 kg·m^-2, 18.47% of S. alterniflora biomass being between 0.73 and 3.00 kg·m^-2; and 6.40% of S. alterniflora biomass being greater than 3.00 kg·m^-2. S. alterniflora with high biomass is mainly distributed in the area near the seawall and the tidal flat towards the seaside. The biomass of S. alterniflora is low between the seawall and the seaside flat. The root mean square error of biomass estimation is 0.76, and the absolute error is between 0.01 and 1.99 kg·m^-2. The above-ground biomass distribution of S. alterniflora in the study area can reflect the inversion results. The distribution of S. alterniflora in the study area is irregular, most of them are distributed in patches. The young S. alterniflora distributed in clusters, which is in the expansion stage of S. alterniflora. The UAV remote sensing method used in this study could simultaneously obtain image of the study area at sampling time, which could be applied to the inversion of biomass with timeline. This study provides a new method for the quantitative inversion of S. alterniflora above-ground biomass.

This study invesitigated the growth and rhizosphere soil bacterial diversity of apple trees with root application of chitosan (CTS) by using 2-year-old Fuji (red Fuji/Malus hupehensis and red Fuji/M. robusta) apple seedlings of different rootstocks as test materials. The results show that the above ground dry weight, root dry weight, root-crown ratio, new shoot length and diameter, root vitality and available nutrient in rhizosphere of young apple trees with root application of CTS were all increased in different degrees. Different treatments of CTS concentrations increased the total root length, root surface area, root-volume and root tip number of young apple trees grafted with M. hupehensis and M. robusta, forming a new root configuration characterized by increasing root length and root tips number. The rhizosphere bacterial diversity of young apple trees with applying of CTS significantly changed. Actinomycetes and proteobacteria were the dominant species in rhizosphere soil of young apple trees, and there were certain differences among different rootstocks. The total bacterial population and the total number of characteristic bacteria in rhizosphere soil decreased in the young apple trees with root application of CTS, but the δ-proteobacteria increased significantly. There were differences on the bacterial community structure in the rhizosphere soil of young apple trees with different rootstocks, and the bacterial community structure in the rhizosphere soil were changed, and some specific bacteria could be selectively enriched by applying different CTS concentrations. Higher concentration of CTS had the greatest effect on the composition and diversity of bacterial community in young apple trees, especially for Proteobacteria. The root configuration parameters and root activity of young apple trees were significantly correlated with the abundances of actinomycetes, proteobacteria and Chloroflexi in the rhizosphere of apple soil.

Arsenic(As) is one of the common pollutants in contaminated sites, and it has strong carcinogenicity. Chemical washing is one of the commonly used remediation technologies for arsenic-contaminated soil, which could remove pollutants from soil in a short time. Although various washing agents have certain elution effects on arsenic-contaminated soils, single washing is difficult to meet the remediation requirements of heavily polluted soils. In order to study the multi-stage washing and remediation effect of different washing agents on arsenic-contaminated soil, a new green chelating washing agent methylglycine diacetic acid (MGDA) and a commonly used phosphate washing agent potassium dihydrogen phosphate (KH₂PO₄) were selected as the washing agents in this study. The indoor three-stage washing simulation experiment was carried out on the heavily arsenic polluted soil with a concentration of 891 mg·kg^-1 (solid-liquid ratio 1∶3). The As removal efficiencies of different washing agents and the changes chemical forms of As in the soil with or without washing agents were analyzed. The results showed that the removal efficiencies of As from soil by 0.12 mol·L^-1 MGDA reached up to 41.11%, which was significantly higher than that by 0.6 mol·L^-1 KH₂PO₄ (28.60%) and by the composite of 0.12 mol·L^-1MGDA and 0.6 mol·L^-1 KH₂PO₄ (10.88%-24.79%). MGDA has better removal efficiencies for aluminum-arsenic, calcium-arsenic and iron-arsenic; and KH₂PO₄ has better removal efficiencies for aluminum-arsenic and iron-arsenic. There were antagonistic effects between MGDA and KH₂PO₄ in the process of composite washing, and they are not suitable for composite washing.

The agronomic characters and physio-chemical indexes of plants under heavy metal pollution will be affected in varying degrees. Arbuscular mycorrhizal fungi (AMF) play an important role in plant response to abiotic stress due to their unique properties. In order to understand the tolerance effect of maize to Pb after symbiosis with arbuscular mycorrhizal fungi (AMF), the environment led by Pb pollution in the maize farmland was simulated using exogenous Pb(NO₃)₂ aging soil for 15 days. The effects of AMF inoculation (Funneliformis mosseae, Fm; Claroideoglomus etunicatum, Ce; Glomus versiforme, Gv) and no AMF inoculation (NM) on the growth of maize at different Pb concentrations (0, 170, 570, 970 mg·kg^-1) were investigated in pot experiment, and the changes of agronomic traits, antioxidant capacity and Pb content of maize inoculated with AMF were analyzed. The results show that the colonization rate of mycorrhizal under Pb contamination was 15.0%-36.0% higher than that without Pb contamination. The height and chlorophyll content of colonized maize were increased by 11.8%-26.8% and 3.9%-7.5%, respectively, and the fresh weight increased by 50%. The translocation factor decreased, meanwhile the Pb content in stem and leaf of maize decreased significantly, but for root it increased significantly (P＜0.05). Resistance analysis indicate that the formation of mycorrhiza inhibited the activity of SOD in maize leaves, but significantly increased the activity of SOD in maize roots, while the activity of POD in the leaves and roots increased. When the concentration of Pb was high, the activity of CAT in roots increased significantly (P＜0.05). The formation of mycorrhiza resulted in the decrease of proline content in maize roots and the increase of soluble protein content in maize leaves and roots (P＜0.05). Under the condition of Pb pollution, AMF inoculation increased the antioxidant capacity of maize, increased the content of soluble protein in maize leaves and roots, and improved the water retention capacity, so as to enhance the resistance of maize to Pb pollution and ensure the normal growth of maize in Pb-contaminated soil. This study provides a theoretical basis for the remediation of heavy metal contaminated soil in farmland and the safe production of crops.

Root exudates play a key role in the rhizo-remediation of pollutants. It will be helpful to understand the mechanism of vetiver in remediating the atrazine-contaminated soil by investigating the characteristics of vetiver root exudates and its effect on the removal of atrazine. In this research, pot experiments were carried out to characterize the vetiver root exudates subjected to 2 mg·kg^-1 of atrazine stress and assess atrazine removal efficiency in soil by adding real vetiver root exudates. The results show that 88 and 83 compounds were detected in the vetiver exudates of atrazine-unadded treatment (CKP) and atrazine-added treatment (ATP), respectively, including alkanes, alkenes, esters, acids, nitriles, ketones, amides, alcohols, and phenols, etc.; Compared with CKP, the number of alkanes reduced by 8.5% under atrazine stress, while the number of alkenes and alcohols increased by 5.5%, and 4.1%, respectively. Meanwhile, the relative concentrations of alcohols and phenols increased by 123.45% and 5.19% under atrazine stress (P<0.05), respectively, while the relative concentrations of nitriles, ketones, acids, alkanes, alkenes, esters, amines and amides decreased. The atrazine removal in soil was significantly enhanced by vetiver root exudates (P<0.05), which was 5.51%-16.99% higher than the control overall. The results suggest that vetiver might adapt to atrazine stress by modulating the number and relative concentrations of the root exudates, such as alkanes, alkenes, alcohols, and phenols. The results of the study can provide a reference for the remediation of atrazine-contaminated soil by vetiver root exudates.

Low-temperature microorganisms have broad application prospects in the long-term, efficient and stable restoration of contaminated media in high latitude and high altitude areas of China. However, the mining of strain resources in specific scenarios is still in its infancy. In this paper, enrofloxacin, one of the common quinolone antibiotics in contaminated soil, was chosen as an aimed contaminants. Four enrofloxacin degrading bacteria of Z (Providencia sp.), H5 (Enterobacter sp.), H35 (Providencia sp.) and Y (Alcaligenes sp.), which were efficient to degrade enrofloxacin at low-temperature, were screened in the soil collected from the livestock and poultry manure stored locality in low-temperature areas. Among them Y was a halophile. Their degradation efficiency was evaluated. The results show that the four strains could grow in a neutral to low alkali environment (livestock and poultry manure stored locality) and a temperature range of 4-15 ℃. The growth of the four strains and their degradation for enrofloxacin were inhibited significantly under low temperature conditions. The natural degradation rates of enrofloxacin were 10.9%, 22.8% and 40.6%, respectively, at 4, 8 and 15 ℃. At 4 ℃, the degradation rate of enrofloxacin by Z, H5, H35 and Y with the dosage of 5% reached the peak on the 14th day, which were 33.4%, 42.1%, 38.1% and 34.3% respectively. However, except H35 ( peaked 56.5% on the 14th day), the degradation rate of enrofloxacin by Z, H5 and Y peaked on the 12th day with the same dosage at 8 ℃, which were 49.6%, 47.9% and 48.1%, respectively. In summary, all of the four strains could be used for the remediation of enrofloxacin contaminated media in low-temperature areas, which provided technical support for the remediation of antibiotic-contaminated soil in high latitude and high altitude regions of China.

The sorption mechanism and effects of pH of Na-montmorillonite dried by two different methods on estrone (E1) were investigated in this study. Freeze-dried and 110 ℃ oven-dried methods were used as the two different drying methods for Na-montmorillonite, and they were used for subsequent sorption isotherms and kinetic experiments. Results show that specific surface area and pore volume of freeze-dried Na-montmorillonite were higher than those of 110 ℃ oven-dried one. However, no significant variations of surface functional groups presented for the two Na-montmorillonites. According to the kinetic results, the two Na-montmorillonites both had rapid sorption rates, reaching sorption equilibrium in 45 min for freeze-dried one and in 20 min for 110 ℃ oven-dried one. Besides, the proposed first-order kinetics equation for the freeze-dried Na-montmorillonite and the pseudo-second-order rate equation for 110 ℃ oven-dried Na-montmorillonite were described. Moreover, the sorption isotherms indicate that freeze-dried Na-montmorillonite had significantly higher sorption affinity with E1 compared to oven-dried Na-montmorillonite. The effects of pH on the sorption of E1 by the two kinds of Na-montmorillonite were comparable. High or low pH value was not conducive to sorption of E1 by Na-montmorillonite, and the optimal pH value for adsorption is 6.

In this study, corn straw biochar was modified to micro-nano-engineered nitrogenous biochar (NBC), and the comparative analysis of the performance of NBC with iron modified biochar (FeBC) and thiol modified biochar (SBC) on Pb²⁺ adsorption in aqueous solutions was conducted. These modified biochars were characterized by SEM and BET, and the Pb²⁺ adsorption behavior of NBC was analyzed by batch adsorption experiments. To better understand the mechanisms of Pb²⁺ adsorption by NBC, a sequential desorption test was performed and the changes of biochar function groups before and after he adsorption were analyzed. The results show that, after modification, the aromaticity was enhanced and hydrophilicity and polarity were weakened, the specific surface area and total pore volume of NBC was increased by 6.30 and 2.68 times, respectively, as compared with the unmodified biochar. The adsorption capacity of the three modified biochar for Pb²⁺ was in the order of NBC > FeBC > SBC. The isothermal adsorption by NBC was better fitted to the Langmuir model, and its maximum adsorption capacity reached to 148.25 mg·g^-1, which was 1.68 and 1.93 times higher than that of FeBC and SBC, respectively. The adsorption kinetics of NBC well fits the pseudo-second order model (R²=0.952 4). Additionally, there are rod-like deposits in pores after the adsorption of Pb²⁺ by NBC. The sorption of Pb²⁺ by biochars likely occurred through greater cation exchange, precipitation, cation-π interactions and complexation. The sequential desorption test results indicate that the contribution of NBC to the adsorption modes of Pb²⁺ was ranked hydrogen bonding (57.98%) > cation exchange (29.98%) > complexation (11.95%) > physical adsorption (0.10%). Therefore, the micro-nano-engineered nitrogenous biochar has good adsorption effect on Pb²⁺ in solution, and could be a promising adsorbent for recovering Pb²⁺ from waste water.

The bed breeding of ducks has been widely used, but long-term breeding bedding would result in the accumulation of heavy metals and salts. Meanwhile, the bedding waste is not always completely mature, which would bring security risks to the reutilization of these bedding wastes. In this study, thermophilic microorganisms were inoculated during aerobic composting of bedding wastes, and the safe amount of composted bedding returned to the field was evaluated through a field experiment. The results show that the bedding wastes can be fully decomposed within 50 days of simple stacking with regular turning. Compared with the non-inoculation control, inoculation of 0.5% thermophilic microbial agent could significantly improve the degradation rate of organic matter, and the seed germination index was increased by 23.8%. The yield of muskmelon treated with 25% compound fertilizer N+75% composted bedding N was the highest, which was 8.17% higher than that of 100% compound fertilizer N treatment. The contents of vitamin C and soluble sugar in muskmelon fruit treated with 25% compound fertilizer N+75% composted bedding N were also the highest. Compared with 100% compound fertilizer N treatment, the composted bedding returning treatments increased the contents of soil organic matter, total nitrogen, ammonia nitrogen, available phosphorus and available potassium. However, the contents of Cr, Cu and Zn in the composted bedding returning treatments were increased by 3.15%, 11.65% and 10.17%, respectively. The soil electric conductivity was 40.19% higher than that of the 100% compound fertilizer N treatment. The contents of heavy metals in melon fruit and soil increased with the increasing proportion of bedding materials. This study provides an important basis for the efficient treatment and safe utilization of the bedding materials for meat duck breeding.

In order to reduce the initial runoff pollution in the rural residential area, a composite engineering consisting of a settling tank, an adjusting tank and a water-collecting flowerbed were constructed near Yuncun Village, Qianhuang Township, Changzhou City to collect the initial runoff and drainage from the catchment area (about 6.00 hm²). Based on the composite engineering, the monitoring test was done. Water samples were taken at the water inlet, the water outlet of the settling tank, the adjusting tank and water-collecting flowerbed. The physical and chemical indexes of water samples, including temperature, pH, dissolved oxygen (DO), total nitrogen (TN), ammonia nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), total phosphorous (TP), chemical oxygen demand (COD_Cr) and suspended solids (SS), were monitored to analyze the total removal rates of pollutants and estimate the reduction of pollutants in the initial runoff by the engineering. The results show that the average values of the total removal rates of TN、NH₄⁺-N、NO₃^--N、TP、COD_Cr and SS were 39.1%, 47.4 %, 29.0%, 33.3%, 33.4% and 43.1%,respectively. The scouring effect to the composite engineering caused by the storm runoff of July 15, 2020 was significant when the pollutant concentrations in the effluent of the engineering were higher than those in the influent except for NH₄⁺-N and COD_Cr. The correlation between the total removal rates of TN and NH₄⁺-N was extremely significant (P<0.01), and the correlation between the total removal rates of COD_Cr and SS was extremely significant (P<0.01). The composition of TP in the influent was mainly dissolved phosphorus. Due to submerged volume in the engineering, the plant biomass was increased and the denitrification capacity of the system was improved, which in turn promoted the reduction of nitrogen and phosphorus pollutants. Base on estimation of annual rainfall, the annual reduction amount of TN, TP and COD_Cr in runoff or drainage by the composite engineering were approximately 2.49, 0.29 and 20.94 kg·a^-1, respectively, and the effluent from the engineering can be used for reclaimed water reuse. How to miniaturize and standardize the composite engineering and improve its purifying efficiency and shock resistance should be the priorities in the future researches, so that it can be promoted and applied in more rural residential areas in Taihu Lake Basin.