Comparative study on plant growth-promoting bacterial inoculation by irrigation and spraying for promoting Bidens pilosa L. phytoremediation of cadmium-contaminated soil.

A field study was conducted to compare FM-1 inoculation by irrigation and spraying for promoting Bidens pilosa L. phytoremediation of cadmium (Cd)-contaminated soil. Cascading relationships between bacterial inoculation by irrigation and spraying and soil properties, plant growth-promoting traits, plant biomass and Cd concentrations in Bidens pilosa L. were explored based on the partial least squares path model (PLS-PM). The results indicated that inoculation with FM-1 not only improved the rhizosphere soil environment of B. pilosa L. but also increased the Cd extracted from the soil. Moreover, Fe and P in leaves play vital roles in promoting plant growth when FM-1 is inoculated by irrigation, while Fe in leaves and stems plays a vital role in promoting plant growth when FM-1 is inoculated by spraying. In addition, FM-1 inoculation decreased the soil pH by affecting soil dehydrogenase and oxalic acid in cases with irrigation and Fe in roots in cases with spraying. Thus, the soil bioavailable Cd content increased and promoted Cd uptake by Bidens pilosa L. To address Cd-induced oxidative stress, Fe in leaves helped to convert GSH into PCs, which played a vital role in ROS scavenging when FM-1 was inoculated by irrigation. The soil urease content effectively increased the POD and APX activities in the leaves of Bidens pilosa L., which helped alleviate Cd-induced oxidative stress when FM-1 was inoculated by spraying. This study compares and illustrates the potential mechanism by which FM-1 inoculation can improve the phytoremediation of Cd-contaminated soil by Bidens pilosa L., suggesting that FM-1 inoculation by irrigation and spraying is useful in the phytoremediation of Cd-contaminated sites.

Plant growth and heavy meal accumulation characteristics of Spathiphyllum kochii cultured in three soil extractions with and without silicate supplementation.

A hydroponic method was conducted to test whether Spathiphyllum kochii is tolerant to multiple HMs as well as to evaluate whether sodium silicate promotes plant growth and alleviates HM stress mainly by assessing biomass, HM accumulation characteristics and antioxidant enzyme activities (AEAs). Three soil extractions from an uncontaminated soil, a comparable lightly HM-contaminated soil (EnSE), and a comparable heavily HM-contaminated soil (ExSE) with or without 1 mM sodium silicate supplementation were used. S. kochii showed no obvious symptoms when cultured in EnSE and ExSE, indicating that it was a multi-HM-tolerant species. The biomass and photosynthesis followed the order: UnSE > EnSE > ExSE, but the opposite order was found for HM concentration, AEAs, and malondialdehyde content. Silicate had no effects on the growth and HM bioaccumulation characteristics of S. kochii cultured in UnSE but exhibited a novel role in decreasing HM uptake by 13.61-41.51% in EnSE and ExSE, respectively, corresponding upregulated AEAs, and reduced malondialdehyde contents, resulting in increased biomass and alleviating HM stress. The activities of peroxidase and superoxide dismutase were upregulated by an increase in soil extraction HM concentration and further upregulated by silicate supplementation, indicating that they were important mechanisms alleviating HM stress in S. kochii.

Phytoremediation is an economical and environmentally friendly technology for the alleviation of heavy metal (HM)-contaminated soil. Improving bioremediation efficiency is crucial for this kind of technology. Many studies have shown that silicon plays a novel role in plant growth and adversity responses, but studies in the field of phytoremediation are limited. In addition, phytoremediation plant species are usually hyperaccumulators or may be tolerant crops, commercial crops, or wild species from mining areas, and the use of landscape species in phytoremediation is limited. This is the first report on the effects of silicate on the multi-HM bioaccumulation characteristics of a garden plant (Spathiphyllum kochii) cultured in uncontaminated and HM-contaminated soil extractions. This study will broaden phytoremediation species screening and enrich our understanding of the mechanisms by which Si supports the bioremediation of HM-contaminated environments.HIGHLIGHTSS. kochii was a multi-heavy metal-tolerant species.Silicon played a novel role in reducing heavy metal concentrations by 14­40% and 14­42% in shoots and roots, respectively.Silicon upregulated antioxidant enzyme activities to alleviate heavy metal stress in plants.

Global perspectives for biochar application in the remediation of heavy metal-contaminated soil: a bibliometric analysis over the past three decades.

Herein, 7,308 relevant documents on biochar application for the remediation of heavy metal (HM)-contaminated soil (BARHMCS) from 1991 to 2020 were extracted from the Web of Science Core Collection and subjected to bibliometric and knowledge mapping analyses to provide a global perspective. The results showed that (1) the number of publications increased over time and could be divided into two subperiods, i.e., the slow growth period (SGP) and rapid growth period (RGP), according to whether the annual publication number was ≥300. (2) A total of 126 countries, 741 institutions, and 1,021 scholars have contributed to this field. (3) These studies are mainly published in Science of the Total Environment, Chemosphere, etc., and are mainly based on the categories of environmental science, soil science, and environmental engineering. (4) The top five keyword clusters for the SGP were biochar, biochar, sorption, charcoal, and HMs, and those for the RGP were adsorption, black carbon, nitrous oxide, cadmium, and pyrolysis. (5) The main knowledge domains and the most cited references during the SGP and RGP were discussed. (6) Future directions are related to biochar application for plant remediation, the mitigation of climate change through increased carbon sequestration, biochar modification, and biochar for HMs and multiple organic pollutants.

Biochar application in the remediation of heavy metal-contaminated soil (BARHMCS) has become a popular research topic worldwide. Many excellent papers on this topic have been published, including some valuable reviews. However, there are no reviews including bibliometric and visual analyses. In the present study, bibliometric and visual analyses of relevant literature in the field of BARHMCS based on the Web of Science Core Collection were carried out to outline the development process of this field at a macro level, clarify the research hotspots, identify the knowledge domains that support this field, and explore future research directions. These efforts will no doubt help readers fully understand BARHMCS from a global perspective and provide a reference for future research. HIGHLIGHTSAn overall global perspective of biochar remediation of heavy metal (HM)-contaminated soil was provided.The main popular research topics of each period were discussed.Knowledge domains were discussed.Five main future research directions were identified based on burst keyword analysis.Biochar modification and its effect on HMs and coexisting organic pollutants should be studied in the future for soil remediation purposes.

Metagenomics reveals taxon-specific responses of soil nitrogen cycling under different fertilization regimes in heavy metal contaminated soil.

Soil deficiency, cyclic erosion, and heavy metal pollution have led to fertility loss and ecological function decline in mining areas. Fertilization is an important way to rapidly replenish soil nutrients, which have a major influence on the soil nitrogen cycling process, but different fertilization regimes have different impacts on soil properties and microbial functional potentials. Here, metagenomic sequencing was used to investigate the different responses of key functional genes of microbial nitrogen cycling to fertilization regimes and explore the potential effects of soil physicochemical properties on the key functional genes. The results indicated that AC-HH (ammonium chloride-high frequency and concentration) treatment significantly increased the gene abundance of norC (13.40-fold), nirK (5.46-fold), and napA (5.37-fold). U-HH (urea-high frequency and concentration) treatment significantly increased the gene abundance of hao (6.24-fold), pmoA-amoA (4.32-fold) norC (7.00-fold), nosZ (3.69-fold), and nirK (6.88-fold). Functional genes were distributed differently among the 10 dominant phyla. The nifH and nifK genes were distributed only in Proteobacteria. The hao gene was distributed in Gemmatimonadetes, Nitrospirae and Proteobacteria. Fertilization regimes caused changes in functional redundancy in soil, and nirK and nirB, which are involved in denitrification, were present in different genera. Fertilization regimes with high frequency and high concentration were more likely to increase the gene abundance at the genus level. In summary, this study provides insights into the taxon-specific response of soil nitrogen cycling under different fertilization regimes, where changes in fertilization regimes affect microbial nitrogen cycling by altering soil physicochemical properties in a complex dynamic environment.

CaFe-layered double hydroxide corn straw biochar reduced heavy metal uptake by Brassica campestris L. and Ipomoea aquatic F.: Rhizosphere effects and oxidative stress alleviation.

In the present study, CaFe-layered double hydroxide corn straw biochar (CaFe-LDH@CSB) was applied to the rhizosphere soil of both pakchoi (Brassica campestris L. ssp. Chinensis Makino, B. campestris L.) and water spinach (Ipomoea aquatic F., I. aquatic F.) to explore and clarify the potential mechanism by which CaFe-LDH@CSB helps vegetables reduce heavy metal (HM) uptake and alleviate oxidative stress. Pot experiments were conducted with CaFe-LDH@CSB applied at four levels: control (CK), T1 (5 g kg-1), T2 (10 g kg-1) and T3 (20 g kg-1). The results indicated that the application of CaFe-LDH@CSB significantly increased pH and decreased the acid-soluble forms of Cd, Pb, Zn and Cu in the rhizosphere soil of both B. campestris L. and I. aquatic F.; decreases of 39.4%, 18.0%, 10.0% and 33.3% in B. campestris L. and of 26.6%, 49.1%, 13.2% and 36.8% in I. aquatic F., respectively, were observed at the T3 level. Moreover, CaFe-LDH@CSB application reduced HM uptake by B. campestris L. and decreased HM-induced oxidative stress through the regulation of soil physicochemical properties and microbial abundance. For B. campestris L., variations in Sordariomycetes helped alleviate the accumulation of HMs in the aerial part, while GSH and -SH from the nonenzymatic system played an important role in scavenging H2O2 in leaves, thus helping B. campestris L. alleviate HM-induced oxidative stress. For I. aquatica F., variations in Vicinamibacteria and Mortierellomycetes helped alleviate the accumulation of HMs in plants, while GSH and PCs from nonenzymatic systems played an important role in removing ·O2- in leaves, thereby helping I. aquatica F. alleviate HM-induced oxidation stress. Our study indicated that the application of CaFe-LDH@CSB improved the rhizosphere soil environment and rebuilt the soil microbial community, helping B. campestris L. and I. aquatica F. alleviate HM-induced oxidative stress and promoting the growth of both vegetables.

Impact of environmental factors on the ammonia-oxidizing and denitrifying microbial community and functional genes along soil profiles from different ecologically degraded areas in the Siding mine.

Ammonia oxidizers (ammonia-oxidizing bacteria (AOB amoA) and ammonia-oxidizing archaea (AOA amoA)) and denitrifiers (encoded by nirS, nirK and nosZ) in the soil nitrogen cycle exist in a variety of natural ecosystems. However, little is known about the contribution of these five N-related functional genes to nitrification and denitrification in the soil profile in severely ecologically degraded areas. Therefore, in the present study, the abundance, diversity and community composition of AOA, AOB, nirS, nirK and nosZ were investigated in the soil profiles of different ecologically degraded areas in the Siding mine. The results indicated that, at the phylum level, the dominant archaea were Crenarchaeota and Thaumarchaeota and the dominant bacteria were Proteobacteria. Heavy metal contents had a great impact on AOA amoA, nirS and nirK gene abundances. AOA amoA contributed more during the ammonia oxidation process and was better adapted for survival in heavy metal-contaminated environments. In addition to heavy metals, the soil organic matter (SOM) content and C/N ratio had strong effects on the AOA and AOB community diversity and structure. In addition, variations in the net ammonification and nitrification rates were proportional to AOA amoA abundance along the soil profile. The soil C/N ratio, soil available phosphorus content and soil moisture influenced the denitrification process. Both soil available phosphorus and moisture were more strongly related to nosZ than to nirS and nirK. In addition, nosZ presented a higher correlation with the nosZ/(nirS + nirK) ratio. Moreover, nosZ/(nirS + nirK) was the key functional gene group that drove the major processes for NH4+-N and NO3--N transformation. This study demonstrated the role and importance of soil property impacts on N-related microbes in the soil profile and provided a better understanding of the role and importance of N-related functional genes and their contribution to soil nitrification and denitrification processes in highly degraded areas in the Siding mine.

Bacterial extracellular polymeric substances: Impact on soil microbial community composition and their potential role in heavy metal-contaminated soil.

In this study, six different treatments involving extracellular polymeric substances (EPS) from Enterobacter sp. FM-1 (FM-1) (no EPS (control), original bacterial cells (FM-1), FM-1 cells with EPS artificially removed (EPS-free cells, EPS-R), different forms of EPS (soluble EPS (S-EPS), loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS)) obtained from FM-1) and three types of soils (non-contaminated soil (NC soil), high-contamination soil (HC soil) and low-contamination soil (LC soil)) were used to investigate the impact of different EPS treatments on soil microbial community composition and their potential role in the remediation of heavy metal (HM)-contaminated soil. The results indicate that the EPS secreted by FM-1 played a vital role in changing soil pH and helped increase soil bio- HMs. In addition, EPS secretion by FM-1 helped increase the soil EPS-polysaccharide and EPS-nucleic acid contents; even in HC soil, where the HM content was relatively high, LB-EPS addition still increased the EPS-polysaccharide and EPS-nucleic acid contents in the soil by 1.18- and 15.54-fold, respectively. FM-1, LB-EPS and TB-EPS addition increased the soil invertase, urease and alkaline phosphatase activities and increased the soil organic matter (SOM), NH4+-N and available phosphorus (AP) contents, which helped regulate soil nutrient reserves. Moreover, the addition of different EPS fractions modified the soil microbial community composition to help microbes adapt to an HM-contaminated environment. In the HC and LC soils, where the HM content was relatively high, the soil bacteria were dominated by Protobacteria, while fungi in the soil were dominated by Ascomycota. Among the soil physicochemical properties, the soil SOM and NH4+-N contents and invertase activity significantly impacted the diversity and community composition of both bacteria and fungi in the soil.

A novel role of sulfate in promoting Mn phytoextraction efficiency and alleviating Mn stress in Polygonum lapathifolium Linn.

A hydroponic method was performed to explore the effects of sulfate supply on the growth, manganese (Mn) accumulation efficiency and Mn stress alleviation mechanisms of Polygonum lapathifolium Linn. Three Mn concentrations (1, 8 and 16 mmol L-1, representing low (Mn1), medium (Mn8) and high (Mn16) concentrations, respectively) were used. Three sulfate (S) levels (0, 200, and 400 µmol L-1, abbreviated as S0, S200 and S400, respectively) were applied for each Mn concentration. (1) The average biomass (g plant-1) of P. lapathifolium was ordered as Mn8 (6.36) > Mn1 (5.25) > Mn16 (4.16). Under Mn16 treatment, S addition increased (P < 0.05) biomass by 29.96% (S200) and 53.07% (S400) compared to that S0. The changes in the net photosynthetic rate and mean daily increase in biomass were generally consistent with the changes in biomass. (2) Mn accumulation efficiency (g plant-1) was ordered as Mn8 (99.66) > Mn16 (58.33) > Mn1 (27.38); and S addition increased (p < 0.05) plant Mn accumulation and Mn transport, especially under Mn16 treatment. (3) In general, antioxidant enzyme activities (AEAs) and malondialdehyde (MDA) in plant leaves were ordered in Mn16 > Mn8 > Mn1. Sulfate addition decreased (P < 0.05) AEAs and MDA under Mn16 treatment, while the changes were minor under Mn1 and Mn8 treatments. (4) Amino acid concentrations generally increased with increasing Mn concentration and S level. In summary, the medium Mn treatment promoted plant growth and Mn bioaccumulation; sulfate, especially at 400 µmol L-1 S, can effectively promote plant growth and Mn accumulation efficiency. The most suitable bioremediation strategy was Mn16 with 400 µmol L-1 S.

Variation, distribution, and diversity of canonical ammonia-oxidizing microorganisms and complete-nitrifying bacteria in highly contaminated ecological restoration regions in the Siding mine area.

Canonical ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) and complete-nitrifying bacteria (comammox) exist in a variety of ecosystems. However, little is known about AOA, AOB and comammox or their contributions to nitrification in the soils of heavily degraded and acidic mine regions. In the present study, the activity, richness, diversity and distribution patterns of AOA, AOB and comammox in the Siding mine area were investigated. Nemerow's multifactor pollution index (PN) values indicated that the soil in all three areas in the Siding mine area was highly contaminated by Cd, Pb, Zn, Mn and Cu. The AOA, AOB and comammox amoA gene copy numbers exhibited significant positive correlations with Pb and Zn levels and PN values, which indicated that the populations of AOA, AOB and comammox underwent adaptation and reproduction in response to pollution from multiple metals in the Siding mine area. Among them, the abundance of AOA was the highest, and AOA may survive better than AOB and comammox under such severely pollution-stressed and ammonia-limited conditions. The phyla Thaumarchaeota and Crenarchaeota may play vital roles in the soil ammonia oxidation process. Unlike AOA, AOB may use soil available phosphorus to help them compete for NH3 and other limiting nutrients with AOA and heterotrophs. Moreover, soil organic matter was the main factor influencing the species diversity of AOB, the ß-diversity of AOB and comammox, and the community composition of AOA, AOB and comammox. Our research will help to explain the role and importance of AOA, AOB and comammox in the different ecological restoration regions in the Siding mine area.

Low Distortion of Noise Filter Realization with 6.34 V/µs Fast Slew Rate and 120 mVp-p Output Noise Signal.

In order to reduce Gaussian noise, this paper proposes a method via taking the average of the upper and lower envelopes generated by capturing the high and low peaks of the input signal. The designed fast response filter has no cut-off frequency, so the high order harmonics of the actual signal remain unchanged. Therefore, it can immediately respond to the changes of input signal and retain the integrity of the actual signal. In addition, it has only a small phase delay. The slew rate, phase delay and frequency response can be confirmed from the simulation results of Multisim 13.0. The filter outlined in this article can retain the high order harmonics of the original signal, achieving a slew rate of 6.34 V/µs and an almost zero phase difference. When using our filter to physically test the input signal with a noise level of 3 Vp-p Gaussian noise, a reduced noise signal of 120 mVp-p is obtained. The noise can be suppressed by up to 4% of the raw signal.

Comparative analysis of the seed germination of pakchoi and its phytoremediation efficacy combined with chemical amendment in four polluted soils.

The seed germination plant growth parameters and level of heavy metal accumulation were investigated in pakchoi cultured in four contaminated soils with different levels of heavy metals supplemented with citric acid (CA) or calcium phosphate (CP). Results showed that the seed germination energy, germination percentage and germination index parameters were similar, while the seed vigor (SV) significantly (p < 0.05) decreased as the soil pollution level increased. The lengths of the shoots and roots presented the same trend as SV. All the seedlings grew in heavily polluted soil without any amendments before harvesting; therefore, no plant material was available for subsequent analyses. The photosynthesis parameters of pakchoi cultured in lightly polluted soil without amendment (LPS), lightly polluted soil with CA (LPSA) and moderately polluted soil with CP (MPSP) were similar. The concentrations of Pb, Zn, Mn, Cu and Cd in the shoots, roots and whole plants were in the order of MPSP > LPSA > LPS. Pakchoi cultured in MPSP showed the most promising results in terms of plant height, biomass and heavy metal accumulation. Pakchoi presented the highest translocation and bioaccumulation factors for Cd and the lowest for Pb.HighlightsSoil pollution and the type of chemical amendment had no effect on the seed germination of pakchoi.Citric acid addition in lightly polluted soil improved pakchoi growth and heavy metal extraction.Pakchoi cultured in moderately polluted soil with calcium phosphate amendment presented the highest biomass and heavy metal concentration.

Manganese accumulation and plant physiology behavior of Camellia oleifera in response to different levels of potassium fertilization.

The effects of potassium (K) fertilization (KCl, analytically pure; 0, 60, 200, and 400 mg kg-1) on the growth and Mn accumulation of Camellia oleifera in two types of Mn-contaminated soils were investigated. The potential mechanisms underlying the impacts of K fertilization were explored. C. oleifera accumulated high amounts of Mn in both soil conditions. The addition of K fertilizer decreased the soil pH and promoted Mn accumulation in C. oleifera. However, the plant biomass decreased significantly under the high level of K fertilization (400 mg kg-1), and the oxidative stress was stimulated under Mn contamination. But an appropriate concentration of K fertilizer (200 mg kg-1) was necessary for the formation of photosynthesis pigments, nonenzymatic antioxidants and antioxidant enzymes, metabolic processes, and nutrient uptake. Furthermore, when plants supplemented with a low level of K fertilization (200 mg kg-1), the catalase activity in C. oleifera leaves was enhanced to alleviate oxidative stress and protect the plant from Mn contamination. Our study demonstrated that 200 mg kg-1 of K fertilizer has the potential to further enhance the efficiency of Mn phytoremediation by C. oleifera.

The effects of EDTA on plant growth and manganese (Mn) accumulation in Polygonum pubescens Blume cultured in unexplored soil, mining soil and tailing soil from the Pingle Mn mine, China.

The effects of water-extractable Mn concentration, bioaccumulation factor (BAF), translocation factor (TF), and Mn uptake by Polygonum pubescens Blume cultured in the unexplored soil, mining soil and tailing soil from the Pingle Mn mine in China were quantified in a pot experiment to determine the effects of EDTA exposure on the success of phytoremediation. The results showed that EDTA significantly (P < 0.05) increased the water-extractable Mn concentration, and soils with different amounts of artificial disturbances had different responses to EDTA exposure. Low and medium EDTA concentrations might have positive effect on plant growth of P. pubescens cultured in the unexplored soil, as indicated by comparable increases in biomass, plant height and photosynthetic pigment content, but opposite results were found with high EDTA concentrations exposure. EDTA exposure had a negative effect on the growth of P. pubescens cultured in the mining soil and tailing soil. In general, the concentration of Mn in different tissues significantly (P < 0.05) increased as the EDTA concentration increased in each soil. The efficacy of Mn remediation by P. pubescens was enhanced in all three soils, with all EDTA treatments.

Manganese accumulation and plant physiology behavior of Camellia oleifera in response to different levels of nitrogen fertilization.

Manganese (Mn) pollution in soil, especially around the mining areas, is a severe problem in China. Seeking for effective remediation methods for Mn-contaminated soil is therefore urgent and necessary. Camellia oleifera (C. oleifera) is one of the world's four major woody oil plants, which is widely cultivated in subtropical acidic soils for oil production and has become an important economic and ecological resource in Guangxi Province. Nitrogen (N) is one of the most common limiting factors for plant growth and development in soils. We carried out this study to evaluate the effects of different N fertilization levels (0, 100, 300 and 500 mg kg-1) on the morphological and physiological characteristics of C. oleifera in two soils with different Mn-contamination degrees. The results indicate that N fertilization affected the plant growth and the content of photosynthetic pigments, while C. oleifera accumulated great amounts of Mn in both soils. However, the plant biomass reduced significantly at the high-level N fertilization (≥300 mg kg-1), and the oxidative stress was stimulated under Mn contamination. As a comparison, the plant biomass remained unaffected at the low-level N fertilization (100 mg kg-1), and the ascorbate peroxidase (APX) activity in C. oleifera leaves were enhanced to alleviate the oxidative stress and therefore protecting the plant from Mn contamination. Meanwhile, plants supplemented with a low-level of N fertilizer (100 mg kg-1) had appropriate antioxidant enzyme and nonenzymatic antioxidant activities, which indicates that this was favorable growth conditions for C. oleifera. Thus, the recommended N fertilization level for maintaining plant biomass and increasing Mn accumulation in plant is 100 mg kg-1 N; at which level the efficiency of Mn phytoremediation by C. oleifera can be further enhanced.

Nitrogen fertilizers promote plant growth and assist in manganese (Mn) accumulation by Polygonum pubescens Blume cultured in Mn tailings soil.

This study examined how different nitrogen (N) forms and application levels promote plant growth and assist in manganese (Mn) remediation of Polygonum pubescens Blume (P. pubescens) cultured in soil with a high Mn level. The effects of ammonium chloride (a) and urea (u), at three application levels (10, 20, and 30 mg L-1 N) and control (no N addition, CK) on the growth, Mn accumulation, and enzymatic anti-oxidative defenses of P. pubescens were examined. In general, both ammonium-N and urea-N promoted the plant mass and height of P. pubescens. The total Mn amount of roots, stems, and leaves in N treatments were higher (p < 0.05) than that of CK. The ammonium-N treatments showed greater plant biomass and Mn accumulation compared to the urea-N ones. In general, the accumulations of Mn, Cr, Zn, and Cu were significantly lower (p < 0.05) in the N fertilizer treatment than those in the control; while the accumulations of Pb were higher (p < 0.05) in P. pubescens across all N fertilizer treatments than those in the control. The N addition decreased the contents of O2- and H2O2 in the leaves of P. pubescens, while increasing the activities of enzymatic anti-oxidative defenses.

A newly found manganese hyperaccumulator--Polygonum lapathifolium Linn.

In the present work, both field investigation and laboratory experiment were carried out to testify whether Polygonum lapathifolium L. is a potential manganese (Mn) hyperaccumulator. Results from field investigation showed that P. lapathifolium had great tolerance and accumulation to Mn. Mn concentrations in leaves were the highest, varied from 6889.2 mg kg-1 dry weight (DW) to 18841.7 mg kg(-1) DW with the average of 12180.6 mg kg(-1). The values of translocation factor (the concentrations of Mn in leaf to that in root) ranged from 5.72 to 9.53. Results from laboratory experiment illuminated that P. lapathifolium could grow well and show no toxic symptoms even under high Mn stress (16 mmol L(-1)). Although the changes of antioxidant enzymes activities were triggered under Mn stress, the alterations of pigments were not significant (P > 0.05) as compared with control. Total plant biomass and plant height increased with increasing Mn supply. Mn concentrations in leaves and stems were constantly greater than those in roots, the ratio of concentrations in leaves to that in roots were 2.58-6.72 and the corresponding values in stems to that in roots were 1.45-3.18. The results showed that P. lapathifolium is a Mn-hyperaccumulator.

Effects of polyethylene microplastics and heavy metals on soil-plant microbial dynamics.

Polyethylene (PE) microplastics are emerging pollutants that pose a significant threat to the environment and human health. However, little is known about the effects of PEs on soil‒plant interactions, especially in heavy metal (HM)-contaminated soil. In this study, the effects of PE on rhizosphere soil enzyme activities, microbial interactions and nutrient cycling processes were analyzed from ecological network and functional gene perspectives for the first time. The results indicated that PE-MP addition significantly reduced the biomass of Bidens pilosa L. In addition, the partial increase in carbon, nitrogen, and phosphorus enzyme activities suggested that the effects of PE as a carbon source on microbial functions in HM-contaminated soil should not be ignored. The average path length of bacterial network nodes was found to be higher than that of fungal network nodes, demonstrating that the bacterial ecological network in PE-MP and HM cocontaminated environments has good buffering capacity against changes in external environmental conditions. Furthermore, structural equation modeling demonstrated that particle size and dosage affect soil nutrient cycling processes and that cycling processes are acutely aware of changes in any factor, such as soil moisture, soil pH and soil nitrogen nutrients. Hence, PE-MP addition in HM-contaminated soil has the potential to alter soil ecological functions and nutrient cycles.

Effect of polyethylene microplastics on antibiotic resistance genes: A comparison based on different soil types and plant types.

Microplastics (MPs) and antibiotic resistance genes (ARGs) are two types of contaminants that are widely present in the soil environment. MPs can act as carriers of microbes, facilitating the colonization and spread of ARGs and thus posing potential hazards to ecosystem safety and human health. In the present study, we explored the microbial networks and ARG distribution characteristics in different soil types (heavy metal (HM)-contaminated soil and agricultural soil planted with different plants: Bidens pilosa L., Ipomoea aquatica F., and Brassica chinensis L.) after the application of MPs and evaluated environmental factors, potential microbial hosts, and ARGs. The microbial communities in the three rhizosphere soils were closely related to each other, and the modularity of the microbial networks was greater than 0.4. Moreover, the core taxa in the microbial networks, including Actinobacteriota, Proteobacteria, and Myxococcota, were important for resisting environmental stress. The ARG resistance mechanisms were dominated by antibiotic efflux in all three rhizosphere soils. Based on the annotation results, the MP treatments induced changes in the relative abundance of microbes carrying ARGs, and the G1-5 treatment significantly increased the abundance of MuxB in Verrucomicrobia, Elusimicrobia, Actinobacteria, Planctomycetes, and Acidobacteria. Path analysis showed that changes in MP particle size and dosage may indirectly affect soil enzyme activities by changing pH, which affects microbes and ARGs. We suggest that MPs may provide surfaces for ARG accumulation, leading to ARG enrichment in plants. In conclusion, our results demonstrate that MPs, as potentially persistent pollutants, can affect different types of soil environments and that the presence of ARGs may cause substantial environmental risks.

Photosynthesis-related physiology and metabolomics responses of Polygonum lapathifolium in contrasting manganese environments.

Manganese (Mn) plays an essential role in plant growth; however, excessive Mn is toxic to plants. Polygonum lapathifolium Linn. was tested as a novel Mn-hyperaccumulating species in our previous study, but the underlying mechanisms of this hyperaccumulation are poorly understood. A hydroponic experiment with (8mmolL-1 ) and without additional Mn (CK) was established to explore the possible mechanisms through the effects on photosynthesis-related physiological characteristics and metabolomics. The results showed that additional Mn increased plant biomass, photosynthesis, and stomatal conductance related to increases in the effective photochemical quantum yield of photosystem II and relative electron transport rate (P <0.05). The results from liquid chromatography-mass spectrometry revealed 56 metabolites differentially accumulated between the plants composing these two groups. Metabolites were enriched in 20 metabolic pathways at three levels (environmental information processing, genetic information processing, and metabolism), of which five metabolic pathways were associated with significant or extremely significant changes (P <0.05). These five enriched pathways were ABC transporters (environmental information processing), aminoacyl-tRNA biosynthesis (genetic information processing), biosynthesis of amino acids , d -arginine and d -ornithine metabolism , and arginine biosynthesis (metabolism). Flavonoids may play a key role in Mn tolerance, as they accumulated more than 490-fold, and the relationship between flavonoids and Mn tolerance needs to be studied in the future.

Effects of sulfate on the photosynthetic physiology characteristics of Hydrocotyle vulgaris under zinc stress.

The effects of sulfate on the zinc (Zn) bioaccumulation characteristics and photophysiological mechanisms of the ornamental plant Hydrocotyle vulgaris were explored using a hydroponic culture under three Zn concentrations (300, 500 and 700mgL-1 ) with (400µmolL-1 ) or without the addition of sulfate. Results showed that: (1) tissue Zn concentrations and total Zn contents increased with increasing hydroponic culture Zn concentrations; and sulfate addition decreased Zn uptake and translocation from roots to shoots; (2) Zn exposure decreased photosynthetic pigment synthesis, while sulfate changed this phenomenon, especially for chlorophyll a under 300mgL-1 Zn treatment; (3) Zn exposure decreased photosynthetic function, while sulfate had positive effects, especially on the photosynthetic rate (Pn ) and stomatal conductance (Gs ); and (4) chlorophyll fluorescence parameters related to light energy capture, transfer and assimilation were generally downregulated under Zn stress, while sulfate had a positive effect on these processes. Furthermore, compared to photosynthetic pigment synthesis and photosynthesis, chlorophyll fluorescence was more responsive, especially under 300mgL-1 Zn treatment with sulfate addition. In general, Zn stress affected photophysiological processes at different levels, while sulfate decreased Zn uptake, translocation, and bioaccumulation and showed a positive function in alleviating Zn stress, ultimately resulting in plant growth promotion. All of these results provide a theoretical reference for combining H. vulgaris with sulfate application in the bioremediation of Zn-contaminated environments at the photophysiological level.