Atmospheric Nitrogen Pollution Control Benefits the Coastal Environment.

Nitrogen is an essential nutrient and a major limiting element for the ocean ecosystem. Since the preindustrial era, substantial amounts of nitrogen from terrestrial sources have entered the ocean via rivers, groundwater, and atmospheric deposition. China serves as a key hub in the global nitrogen cycle, but the pathways, sources, and potential mitigation strategies for land-ocean nitrogen transport are unclear. By combining the CHANS, WRF-Chem, and WNF models, we estimated that 8 million tonnes (Tg) of nitrogen was transferred into the ocean in 2017 in China, with atmospheric deposition contributing 1/3. About half variation of the offshore chlorophyll concentration was explained by atmospheric deposition. The Bohai Sea was the hot spot of nitrogen input, estimated at 214 kg N ha-1, while other areas were around 25-51 kg N ha-1. The largest contributors are agricultural systems (4 Tg, 55%), followed by domestic sewage (2 Tg, 21%). Abatement measures could reduce nitrogen export to the ocean by 43%, and mitigating ammonia and nitrogen oxide emissions accounts for 33% of this reduction, highlighting the importance of addressing air pollution in resolving ocean pollution. The cost-benefit analysis suggests the priority of nitrogen reduction in cropland and transport systems for the ocean environment.

Composition of DOM along the depth gradients in the paddy field treated with crop straw for 10 years.

Crop straw return is a widely used agricultural management practice. The addition of crop straw significantly alters the pool of dissolved organic matter (DOM) in agricultural soils and plays a pivotal role in the global carbon (C) cycle, which is sensitive to climate change. The DOM concentration and composition at different soil depths could regulate the turnover and further storage of organic C in terrestrial systems. However, it is still unclear how crop straw return influences the change in DOM composition in rice paddy soils. Therefore, a field experiment was conducted in which paddy soil was amended with crop straw for 10 years. Two crop straw-addition treatments [NPK with 50% crop straw (NPK+1/2S) and NPK with 100% crop straw (NPK + S)], a conventional mineral fertilization control (NPK) and a non-fertilized control were included. Topsoil (0-20 cm) and subsoil (20-40 cm) samples were collected to investigate the soil DOM concentration and compositional structure of the profile. Soil nutrients, iron (Fe) fraction, microbial biomass carbon (MBC), and concentration and optical properties (UV-Vis and fluorescence spectra) of soil DOM were determined. Here, we found that the DOM in the topsoil was more humified than that in the subsoil. The addition of crop straw further decreased the humidification degree of DOM in the subsoil. In crop straw-amended topsoil, microbial decomposition controlled the composition of DOM and induced the formation of aromatic DOM. In the straw-treated subsoil, selective adsorption by poorly crystalline Fe(oxyhydr)oxides and microbial decomposition controlled the composition of DOM. In particular, the formation of protein-like compounds could have played a significant role in the microbial degradation of DOM in the subsoil. Overall, this work conducted a case study within long-term agricultural management to understand the changes in DOM composition along the soil profile, which would be further helpful for evaluating C cycling in agricultural ecosystems.

CH4 and CO2 emissions in water networks of rice cultivation regions.

Rice cultivation regions have a high density of open water networks to meet the requirements of rice growth and production. These open water networks have a significant risk of carbon (C) emissions due to agricultural production, but the C emissions from these waters are not clearly recorded in previous studies. Therefore, this study aimed to explore the pattern and internal mechanism of methane (CH4) and carbon dioxide (CO2) emissions from multiple types of waters (i.e., river, fish pond, reservoir, and ditch) in a typical rice cultivation region in southwestern China. The annual CH4 and CO2 fluxes were higher in the downstream river (2.79-94.89 and 39.39-1699.98 mg m-2 h-1) and ditch (8.80-74.99 and 123.43-542.65 mg m-2 h-1, respectively) and lower in the reservoir (-0.67 to 3.45 and -239.15 to 141.50 mg m-2 h-1) (P < 0.05). The monthly trends of CH4 and CO2 fluxes from the middle river and ditch were driven by interactive reactions of rice cultivation practices and precipitation. In contrast, the emission patterns of CH4 and CO2 from the lower river, upper river, and fish pond were mainly driven by domestic sewage discharge, precipitation, and aquaculture practices, respectively. This study suggested that river and ditch were more sensitive to C emissions than other waters, and the rice production period was the critical period for controlling C emission. Although rice paddy soils yield more cumulative emissions of CH4, water networks in rice cultivation regions were possible hotspots for C emissions due to the higher emission intensities, which were largely overlooked before. Thus, it is necessary to refine and promote practices to better mitigate C emissions from waters in rice cultivation regions in the future.

Incorporating agricultural practices in digital mapping improves prediction of cropland soil organic carbon content: The case of the Tuojiang River Basin.

Accurate mapping of soil organic carbon (SOC) in cropland is essential for improving soil management in agriculture and assessing the potential of different strategies aiming at climate change mitigation. Cropland management practices have large impacts on agricultural soils, but have rarely been considered in previous SOC mapping work. In this study, cropland management practices including carbon input (CI), length of cultivation (LC), and irrigation (Irri) were incorporated as agricultural management covariates and integrated with natural variables to predict the spatial distribution of SOC using the Extreme Gradient Boosting (XGBoost) model. Additionally, we evaluated the performance of incorporating agricultural management practice variables in the prediction of cropland topsoil SOC. A case study was carried out in a traditional agricultural area in the Tuojiang River Basin, China. We found that CI was the most important environmental covariate for predicting cropland SOC. Adding cropland management practices to natural variables improved prediction accuracy, with the coefficient of determination (R2), the root mean squared error (RMSE) and Lin's Concordance Correlation Coefficient (LCCC) improving by 16.67%, 17.75% and 5.62%, respectively. Our results highlight the effectiveness of incorporating agricultural management practice information into SOC prediction models. We conclude that the construction of spatio-temporal database of agricultural management practices derived from inventories is a research priority to improve the reliability of SOC model prediction.

Copper accumulation and physiological markers of soybean (Glycine max) grown in agricultural soil amended with copper nanoparticles.

Copper-based nanoparticles (NPs) display a strong potential to replace copper salts (e.g., CuSO4) for application in agricultures as antimicrobial agents or nutritional amendments. Yet, their effects on crop quality are still not comprehensively understood. In this study, the Cu contents in soybeans grown in soils amended with Cu NPs and CuSO4 at 100-500 mg Cu/kg and the subsequent effects on the plant physiological markers were determined. The Cu NPs induced 29-89% at the flowering stage (on Day 40) and 100-165% at maturation stage (on Day 100) more Cu accumulation in soybeans than CuSO4. The presence of particle aggregates in the root cells with deformation upon the Cu NP exposure was observed by transmission electron microscopy. The Cu NPs at 100 and 200 mg/kg significantly improved the plant height and biomass, yet significantly inhibited at 500 mg/kg, compared to the control. In leaves chlorophyll-b was more sensitive than chlorophyll-a and carotenoids to the Cu NP effect. The Cu NPs significantly decreased the root nitrogen and phosphorus contents, while they significantly increased the leaf potassium content in comparison with control. Our results imply that cautious use of Cu NPs in agriculture is warranted due to relatively high uptake of Cu and altered nutrient quality in soybeans.

Nitrogen addition may promote soil organic carbon storage and CO2 emission but reduce dissolved organic carbon in Zoige peatland.

With the increase of nitrogen (N) deposition, N input can affect soil C cycling since microbes may trigger a series of activities to balance the supply and demand of nutrients. However, as one of the largest C sinks on earth, the role of extra N addition in affecting peatland soil C and its potential mechanism remains unclear and debated. Therefore, this study chose the largest peatland in China (i.e., Zoige, mostly N-limited) to systematically explore the potential changes of soil C, microbes, and ecoenzymes caused by extra N input at the lab scale incubation. Three different types of soils were collected and incubated with different levels of NH4NO3 solution for 45 days. After incubation, N input generally increased soil organic C (SOC) but decreased dissolved organic carbon (DOC) in Zoige peatland soils. Moreover, CO2 and CH4 emissions were significantly increased after high N input (equal to 5 mg NH4NO3 g-1 dry soils). Through a series of analyses, it was observed that microbial communities and ecoenzyme activities mainly influenced the changes of different C components. Collectively, this study implied that the increasing N deposition might help C sequestration in N-limited peatland soils; simultaneously, the risk of increased CO2 and CH4 by N input in global warming should not be ignored.

The insufficient extraction of DNA from swine manures may underestimate the abundance of antibiotic resistance genes as well as ignore their potential hosts.

Swine manure is considered as an extensive reservoir of antibiotic resistance genes (ARGs) spreading in the natural environment after application in soils. To understand whether ARGs abundance in swine manure is underestimated and the hosts are ignored, this study successively extracted DNA from swine manure six times and determined the abundance of several ARGs, class I integron (intI1), and 16S rRNA as well as the microbial communities. It is found that successive six DNA extraction of swine manures elevated the yield of DNA and strongly increased the abundance of ARGs, intI1, and 16S rRNA. Compared with single DNA extraction, the most dominant bacterial phylum in swine manures shifted from Proteobacteria to Firmicutes, and the dominant bacterial genera changed from Acinetobacter Clostridium after six DNA extraction. The ignored abundance of bacterial phylum and genus emphasized the possible hosts carrying these genes should be paid more attention. It is suggested that the successive DNA extraction of manures is required in the future study to improve the knowledge of estimating the risk and hosts of ARGs in manures entering the environment.

Emission of CO2 and CH4 from a multi-ditches system in rice cultivation region: Flux, temporal-spatial variation and effect factors.

Man-made multi-level ditches system is designed to irrigate, drain and collect runoff from surrounding fields. It is not only the conduit of water and field carbon, but also the linear-like wetland with complex carbon cycling. However, the contribution of ditches system to CO2 and CH4 emission has rarely been assessed. To understand the emission pattern of CO2 and CH4 from ditches, this study investigated the emission fluxes of CO2 and CH4 in a three-level ditches system in Chengdu Plain, China. The results showed that the emission of CO2 and CH4 ranged from 70.38 to 950.40 mg C m-2 h-1 and 6.51-74.99 mg C m-2 h-1, respectively, and was higher in spring and summer than other seasons in all ditches (P < 0.05). On the other hand, the emission of CO2 and CH4 increased along with the decreasing ditches size. Besides, it is found that the precipitation, water table depth and water DO concentration might contribute to the emission of CO2, while CH4 was possibly influenced by precipitation, water table depth, temperature, water DO and DOC concentration. Moreover, it is suggested that terrestrial external input and in-situ metabolism might be the main sources of C emission, and in-situ source might largely contribute to CH4 emission. To reduce the C emission, it is necessary to improve fertilization and irrigation methods, limit soil pollutants transferring into ditches, and frequently dredge sediments in future.

Estimating the remaining atmospheric environmental capacity using a single-box model in a high pollution risk suburb of Chengdu, China.

The atmospheric pollution has been the public attention in recent years. In order to better coordinate economic development and atmospheric environmental management, China introduced the concept of atmospheric environmental capacity (AEC). The remaining atmospheric environmental capacity (RAEC) calculated by existing atmospheric pollution sources and AEC is an important basis for regional development and environmental protection. The RAEC of the high-pollution risk suburb of Chengdu in 2015 was estimated by the single-box model and analyzed on multiple time scales. The results show that the RAEC of SO2 and NO2 in this region is 3299 t/a and 2849 t/a, respectively under the annual time scale. However, in the daily time scale, the RAEC of NO2 is negative for 3 days, that is, there are 3 days with serious air pollution. Therefore, it is not appropriate to plan the industrial area only by relying on annual RAEC. Especially, RAEC displays inter-seasonal and monthly variability. On the one hand, in plain areas with low wind speed and little change in wind direction, achieving the prediction of atmospheric mixing layer height could give early warning of atmospheric pollution events. On the other hand, different management measures are taken on different time scales. On a long timescale, the regional energy structure should be optimized. On seasonal and monthly time scales, the production plans should be adapted to RAEC. On the daily time scale, it mainly deals with the serious atmospheric pollution accident timely.

The characterization of biochars derived from rice straw and swine manure, and their potential and risk in N and P removal from water.

Nowadays, the plant residual derived biochars have been widely applied to remove nitrogen (N) and phosphorus (P) from water. However, the application of animal manure derived biochars in N and P removal was less studied. To compare the different efficiency and risk of plant residual- and animal manure-derived biochar in removing N and P from water, this study chose rice straw and swine manure as representative to produce biochar at 700 °C, and modified the produced biochar by MgCl2. Then, the characteristics, removal efficiency and release of N and P of biochars were investigated. The results showed swine manure-biochars generally had higher ash content and cation exchange capacity (CEC), but lower pH and surface area relative to rice straw-biochars. Besides, MgCl2 modification reduced the ash content and surface area of both raw biochars, whereas the pH, CEC and pore size were enhanced. Furthermore, this work demonstrated that ammonium and nitrate could be removed by all biochars to certain extent, and MgCl2 modified biochars generally had higher removal efficiency. However, none of phosphate removal was achieved by all biochars. Additionally, the release of ammonium, nitrate and phosphate from biochars was observed, suggesting there might be a risk for applying biochars in N and P removal from water. Notably, the MgCl2 modification seemed to accelerate N and P release from biochars. This work provided important information that the production and modification of biochars should be carefully designed for higher removal efficiency of pollutants. Meanwhile, the risk of released pollutants as well as the release mechanisms should be paid more attention in the future.

Quantification of sources and potential risks of cadmium, chromium, lead, mercury and arsenic in agricultural soils in a rapidly urbanizing region of southwest China: the case of Chengdu.

Rapid urbanization a major factor affecting heavy metal contamination on suburban agricultural soils. In order to assess the dynamic contamination of heavy metals in soil from agricultural land bordering a rapidly urbanizing area and the transfer of human health risks from contaminants in this process, 186 and 293 soil samples from agricultural land in suburban Chengdu were collected in September 2008 and September 2017, respectively. Several indicators, such as the integrated pollution index (PI) and the potential ecological risk index (RI), were employed for analyzing the heavy metal contamination levels, and the APCS-MLR receptor model were applied for analyzing the heavy metal sources. As a result, mean concentrations for five elements did not exceed the national soil pollution risk screening values in the two periods mentioned above. Nemerow's composite contamination index revealed an increase in soil contamination of arable land after 10 years of urbanization, with 3.75 and 1.02% of light and moderate sample plots, respectively, by 2017. The assessment for potential ecological risk indicated an increased level of eco-risk to high for most of the sample plots. Based on the APCS-MLR model, the origin and contribution to the five elements varied considerably between the two periods mentioned above. Among them, soil Pb changed from "industrial source" to "transportation source," soil Cr changed from "natural source" to "transportation source," and As and Hg changed from "industrial source" to "transportation source." As and Hg were associated with agricultural activities in both periods, and Cd was derived from industrial activities in both periods. The study suggests that inhalation has become a major contributor to non-cancer health risks in urbanization, unlike intake routes in previous periods, and that the increase in cancer risk is mainly due to children's consumption of agricultural products with As residues. The change in the main source of As to "transportation" also indicates a decrease in air quality during urbanization and the development of the transportation industry. This study provides a reference for the governments of rapidly urbanizing cities to formulate relevant highway and agricultural policies to safeguard the health of the people based on the current situation.

The fate of antibiotic resistance genes in wastewater containing microalgae treated by chlorination, ultra-violet, and Fenton reaction.

Antibiotic resistance genes (ARGs) and bacteria (ARBs) in the effluent of wastewater treatment plants (WWTPs) are of utmost importance for the dissemination of ARGs in natural aquatic environments. Therefore, there is an urgent need for effective technologies to eliminate WWTP ARGs/ARBs and mitigate the associated risks posed by the discharged ARG in aquatic environments. To test the effective technology for eliminating ARGs/ARBs, we compared the removal of ARGs and ARBs by three different tertiary treatments, namely ultra-violet (UV) disinfection, chlorination disinfection, and Fenton oxidation. Then, the treated wastewater was co-cultured with Chlorella vulgaris (representative of aquatic biota) to investigate the fate of discharged ARGs into the aquatic environment. The results demonstrated that chlorination (at a chlorine concentration of 15 mg/L) and Fenton (at pH 2.73, with 0.005 mol/L Fe2+ and 0.0025 mol/L H2O2) treatment showed higher efficacy in ARG removal (1.8 - 4.17 logs) than UV treatment (15 min) (1.29 - 3.87 logs). Moreover, chlorine at 15 mg/L and Fenton treatment effectively suppressed ARB regeneration while UV treatment for 15 min could not. Regardless of treatments tested in this study, the input of treated wastewater to the Chlorella system increased the number of ARGs and mobile genetic elements (MGEs), indicating the potential risk of ARG dissemination associated with WWTP discharge. Among the wastewater-Chlorella co-culture systems, chlorination resulted in less of an increase in the number of ARGs and MGEs compared to Fenton and UV treatment. When comparing the wastewater systems to the co-culture systems, it was observed that Chlorella vulgaris reduced the number of ARGs and MGEs in chlorination and UV-treated wastewater; however, Chlorella vulgaris promoted ARG survival in Fenton-treated water, suggesting that aquatic microalgae might act as a barrier to ARG dissemination. Overall, chlorination treatment not only effectively removes ARGs and inhibits ARB regeneration but also shows a lower risk of ARG dissemination. Therefore, chlorination is recommended for practical application in controlling the spread of discharged ARGs from WWTP effluent in natural aquatic environments.

A bibliometric analysis of global research hotspots and progress on microplastics in soil‒plant systems.

Plastic pollution has become a global and persistent challenge, posing threats to ecosystems and organisms. In recent years, there has been a rapid increase in scientific research focused on understanding microplastics in the soil‒plant system. This surge is primarily driven by the direct impact of microplastics on agricultural productivity and their association with human activities. In this study, we conducted a comprehensive bibliometric analysis to provide an overview of the current research on microplastics in soil‒plant systems. We systematically analysed 192 articles and observed a significant rise in research interests since 2017. Notably, China has emerged as a leading contributor in terms of published papers, closely followed by Germany and the Netherlands. Through co-authorship network analysis, we identified 634 different institutions that participated in publishing papers in this field, with the Chinese Academy of Sciences having the most collaborations. In the co-occurrence keyword network, we identified four clusters focusing on the diversity of microplastics within the agroecosystem, transportation, and quantification of microplastics in soil, analysis of plastic contamination type and impact, and investigation of microplastic phytotoxicity. Furthermore, we identified ten research priorities, categorized into the effects of microplastics in "soil" and "plant". The research hotspots were found to be the effect of microplastics on soil physicochemical properties and the synergistic phytotoxicity of microplastics with other pollutants. Overall, this bibliometric analysis holds significant value, serving as an important reference point and offering valuable suggestions for future researchers in this rapidly advancing field.

Synergizing economic growth and carbon emission reduction in China: A path to coupling the MFLP and PLUS models for optimizing the territorial spatial functional pattern.

Carbon emissions caused by economic growth are the main cause of global warming, but controlling economic growth to reduce carbon emissions does not meet China's conditions. Therefore, how to synergize economic growth and carbon emission reduction is not only a sustainable development issue for China, but also significant for mitigating global warming. The territorial spatial functional pattern (TSFP) is the spatial carrier for coordinating economic development and carbon emissions, but how to establish the TSFP of synergizing economic growth and carbon emission reduction remains unresolved. We propose a decision framework for optimizing TSFP coupled with the multi-objective fuzzy linear programming and the patch-generating land use simulation model, to provide a new path to synergize economic growth and carbon emission reduction in China. To confirm the reliability, we took Qionglai City as the demonstration. The results found a significant spatiotemporal coupling between TSFP and the synergistic states between economic growth and carbon emission reduction (q ≥ 0.8220), which resolves the theoretical uncertainty about synergizing economic growth and carbon emission reduction through the path of TSFP optimization. The urban space of Qionglai City in 2025 and 2030 obtained by the decision framework was 6497.57 hm2 and 6628.72 hm2 respectively, distributed in the central and eastern regions; the rural space was 60,132.92 hm2 and 56,084.97 hm2, concentrated in the east, with a few located in the west; and the ecological space was 71,072.52 hm2 and 74,998.31 hm2, mainly located in the western and southeastern areas. Compared with the TSFP in 2020, the carbon emission intensity of the TSFP obtained by the decision framework was reduced by 0.7 and 4.7 tons/million yuan, respectively, and realized the synergy between economic growth and carbon emission reduction (decoupling index was 0.25 and 0.21). Further confirming that TSFP optimization is an effective way to synergize economic growth and carbon emission reduction, which can provide policy implications for coordinating economic growth and carbon emissions for China and even similar developing countries.

Managing fragmented croplands for environmental and economic benefits in China.

Cropland fragmentation contributes to low productivity and high abandonment risk. Using spatial statistics on a detailed land use map, we show that 10% of Chinese croplands have no potential to be consolidated for large-scale farming (>10 ha) owing to spatial constraints. These fragmented croplands contribute only 8% of total crop production while using 15% of nitrogen fertilizers, leading to 12% of fertilizer loss in China. Optimizing the cropping structure of fragmented croplands to meet animal food demand in China can increase animal food supply by 19%, equivalent to increasing cropland proportionally. This crop-switching approach would lead to a 10% and 101% reduction in nitrogen and greenhouse gas emissions, respectively, resulting in a net benefit of US$ 7 billion yr-1. If these fragmented croplands were relocated to generate large-scale farming units, livestock, vegetable and fruit production would be increased by 8%, 3% and 14%, respectively, and reactive nitrogen and greenhouse gas emissions would be reduced by 16% and 5%, respectively, resulting in a net benefit of US$ 44 billion yr-1. Both solutions could be used to achieve synergies between food security, economic benefits and environmental protection through increased agricultural productivity, without expanding the overall cropland area.

Managing urban development could halve nitrogen pollution in China.

Halving nitrogen pollution is crucial for achieving Sustainable Development Goals (SDGs). However, how to reduce nitrogen pollution from multiple sources remains challenging. Here we show that reactive nitrogen (Nr) pollution could be roughly halved by managed urban development in China by 2050, with NH3, NOx and N2O atmospheric emissions declining by 44%, 30% and 33%, respectively, and Nr to water bodies by 53%. While rural-urban migration increases point-source nitrogen emissions in metropolitan areas, it promotes large-scale farming, reducing rural sewage and agricultural non-point-source pollution, potentially improving national air and water quality. An investment of approximately US$ 61 billion in waste treatment, land consolidation, and livestock relocation yields an overall benefit of US$ 245 billion. This underscores the feasibility and cost-effectiveness of halving Nr pollution through urbanization, contributing significantly to SDG1 (No poverty), SDG2 (Zero hunger), SDG6 (Clean water), SDG12 (Responsible consumption and production), SDG14 (Climate Action), and so on.

Ecological spatial intensive use optimization modeling with framework of cellular automata for coordinating ecological protection and economic development.

With the exposure of excessive intensive use of urban and agricultural space, the optimization of intensive use of ecological space provides a new way to coordinate the global problem of spatial conflict between ecological protection and economic development. However, the coupling accuracy of the existing structure-spatial coupling optimization model is low, which cannot provide method support for the optimization of intensive use of ecological space. To solve this problem, we propose a new model of ecological spatial intensive use optimization (ESIUO) based on the non-stationarity of the Markov state transition probability of the dominant ecosystem service functions (DESFs) and their suitability, and with the help of the framework of cellular automata (CA). We took Qionglai City as an empirical study area, and compared the results of this model with those of CA-Markov and CLUE-S models with the same parameters. The results show that: (i) The quantitative structure corresponding to the spatial layout of each dominant ecosystem service function (DESF) optimized by the ESIUO model has the smallest relative error (δk≤0.04%) with the optimal quantitative structure. (ii) The layout of DESFs optimized by the ESIUO model maximizes the supply capacity of ecosystem services. The minimum matching degree between the distribution of each DESF and the high-value area of its suitability is 92.06 %, and the spatial distribution is more compact, and the comprehensive effect of spatial layout is the best. Further analysis confirmed that the model can establish the spatial layout of DESFs that can realize the high precision coupling with the optimal quantitative structure of DESFs in terms of quantitative structure, and can support the construction of the layout of intensive use of ecological space to alleviate the pressure of non-ecological space expansion in these areas, and then provide a new way to coordinate ecological protection and economic development.

Conversion of swine manure into biochar for soil amendment: Efficacy and underlying mechanism of dissipating antibiotic resistance genes.

Livestock manure amendment, a common fertilization method for agricultural practice, can exacerbate antibiotic resistance gene (ARG) pollution, thus threatening food safety and human health. On the other hand, manure can also be produced as biochar to improve soil quality, which may reduce ARGs inside manure. However, it is unclear how and why shifting manure to biochar for soil amendment reduces ARG pollution. Thus, this study investigated the variations of ARGs and microbial communities in soil amended with swine manure (2 % and 5 %) and its biochar (2 % and 5 %) and then explored how shifting swine manure to biochar reduced ARG contamination. After 28 d incubation, ARG number in soil without amendment, manure-amended soils, and biochar-amended soils were 47, 112-136, and 43-52, respectively. ARG abundance in soil without amendment, manure-amended soils, and biochar-amended soils were 7.66 × 107, 4.32 × 109 - 1.42 × 1011, and 8.44 × 107-9.67 × 107 copies g-1 dry soil, respectively. Compared to manure-amended soils, its biochar amendments reduced ARG abundance by 2-4 orders of magnitude and ARG number by 70-93 in soil. Besides, manure amendment altered while biochar did not alter bacterial diversity and composition. The changed soil properties and mobile genetic elements (MGEs) could explain the changes in ARGs. Relative to manure amendments, its biochar amendments reduced mobile genetic elements (MGEs), Proteobacteria and Bacteroidetes in soil, which explained the reduced abundance and diversity of ARGs; however, the multidrug-resistance genes harbored in Proteobacteria and Bacteroidetes were still abundant in biochar-amended soil. This study suggests that converting manure to biochar as a soil amendment can help control the spread of manure ARGs.

Allelopathic effect of pyrogallic acid on cyanobacterium Microcystis aeruginosa: The regulatory role of nitric oxide and its significance for controlling harmful algal blooms (HABs).

Utilization of allelochemicals to inhibit overgrowth of toxic cyanobacteria is considered to be an environmentally friendly approach. However, the regulatory role of the signaling molecule nitric oxide (NO) on cyanobacteria under allelopathic stress remains unanswered. Here we demonstrate that the effect of NO on the cyanobacterium Microcystis aeruginosa depends on allelopathic stress of pyrogallic acid (PA). The experimental results revealed that general stimulation of M. aeruginosa by PA occurred within the concentration range 0.4-0.8 mg/L. In parallel with increasing concentration of PA (1.6-16.0 mg/L), the growth of M. aeruginosa was observed to decrease. The effect of NO on M. aeruginosa was evaluated by addition of the NO scavenger hemoglobin. In the stimulation stage, intracellular NO was seen to decreased to modulate the level of reactive oxygen species (ROS) and to maintain redox homeostasis of the cells. In the inhibition stage, the physiological characteristics of M. aeruginosa were changed significantly. Additionally, the accumulation of S-nitrosothiol by M. aeruginosa indicated that the high concentrations of PA induced nitric oxidative stress in M. aeruginosa. This study provides a new thought to understand the role of NO in controlling harmful algal blooms through the allelopathic effect of aquatic macrophytes.

A novel bio-washing eluent obtained from fermentation of fruit wastes for removal of soil Pb: efficiency, mechanism, and risk assessment.

Agricultural wastes are inexpensive materials for soil remediation. However, the direct water extracts from these wastes showed low efficiency for Pb removal, thus limiting their application. In this study, citrus pericarp (CP) and pineapple peel (PP), as the common agricultural wastes, were inoculated with lactic acid bacteria to produce fermentation liquors (FCP and FPP) for improving Pb removal efficiency. Results showed that the Pb removal rates by FCP and FPP reached 37.3 and 43.6%, and increased by almost 50.0% than those by CP and PP. The ecological risk of Pb reduced by 83.0-88.2% after five times continuous washing with FCP and FPP, and the Pb concentrations conformed to soil remediation standard of China. Moreover, soil organic carbon 1.5 times increased in the washed soils, while total potassium improved by 40.7-68.0%. The mechanisms of Pb removal by these wastes involved in adsorption-desorption of Pb2+, complexation with organic ligands, and co-precipitation of Pb complexes. The increase of low molecular organic acids during the fermentation promoted dissolution of Pb and provided more hydroxyl, carboxyl, and amine groups to interact with Pb2+, thus improving its removal rate. Therefore, fermentation liquid from fruit wastes is a novel, effective, and ecofriendly bio-washing eluent for Pb removal from contaminated soils.