Influence of root components of celery on pyrene bioaccessibility, soil enzymes and microbial communities in pyrene and pyrene-diesel spiked soils

Snow-cover loss attenuates the effects of N addition on desert nutrient cycling and microbial community

Desert ecosystems are sensitive to nitrogen (N) deposition. Considering snow is an important source of soil water, which is vital for plant growth and the biogeochemical cycle in desert areas. The effects of N deposition on biological soil crusts (BSCs) could be impacted by the removal of snow-cover. Here, we established a split-plot experiment in the Gurbantunggut Desert to examine the effects of snow-cover treatments on soil nutrients, enzyme activities, and the bacterial community under various N addition. The removal of snow-cover reduced the soil nutrients with light and moderate N addition, it also reduced the activities of urease (URE) and alkaline phosphatase (PHOS). The structural equation model (SEM) result indicated that low soil moisture (SMO) under snow-uncover inhibited the bacterial community, particularly suppressed bacterial diversity. Additionally, N addition indirectly affected the bacterial community via modifications to soil nutrients, and soil organic matter (SOM) (P < 0.001) was the crucial factor. Snow-uncover weakened soil nutrient and enzyme responses to N addition, indicating that snow-cover removal reduced the sensitivity of the desert ecosystem to N deposition. The study highlights the critical role of snow-cover in the desert ecosystem, raising our awareness of the ecological risks of BSCs in future global change.

Isolation, characterization and application of the epoxiconazole-degrading strain Pseudomonas sp. F1 in a soil-vegetable system

Epoxiconazole (EPX) has a long half-life in soil and causes various toxicological effects in both the ecosystem and mammals. In this study, eight strains of bacteria capable of degrading EPX were isolated from pesticide-contaminated soil, with strain F1 showing the best effect. This strain was identified as Pseudomonas sp. by 16S rRNA gene sequencing and physiological-biochemical analyses. Our results indicated that strain F1 has a high capacity to degrade EPX, removing 92.1% of EPX within 6 days. The temperature and pH were the two most important environmental factors affecting EPX degradation, followed by substrate concentration and inoculum dose. In addition, strain F1 has a high capacity to promote EPX degradation in soils, with a lower t_1/2 value (2.64 d) in F1-inoculated soil compared to the control (t_1/2 = 96.3 d) without strain F1. The strain could efficiently colonize rhizosphere soil and enhance degradation of EPX, leading to a significant decrease in the accumulation and translocation of EPX in vegetables, thereby alleviating the effects of EPX-induced stress on plants. Moreover, we observed that strain F1-gfp was able to colonize the roots, stems and leaves of Brassica rapa var. chinensis. Such colonization may play a role in the efficient degradation of EPX within plants. To our knowledge, this is the first study to demonstrate biodegradation of EPX in a soil-vegetable system using an EPX-degrading bacterium. This study indicates that strain F1 is a promising candidate for simultaneous bioremediation of soil contaminated with EPX and safe food production.

Mangrove's rhizospheric engineering with bacterial inoculation improve degradation of diesel contamination

Mangroves (Avicennia marina) growing in intertidal areas are often exposed to diesel spills, adversely damaging the ecosystem. Herein, we showed for the first time that mangrove seedlings' associations with bacteria could reprogram host-growth, physiology, and ability to degrade diesel. We found four bacterial strains [Sphingomonas sp.-LK11, Rhodococcus corynebacterioides-NZ1, Bacillus subtilis-EP1 Bacillus safensis-SH10] exhibiting significant growth during diesel degradation (2% and 5%, v/v) and higher expression of alkane monooxygenase compared to control. This is in synergy with reduced long-chain n-alkanes (C24-C30) during microbe-diesel interactions in the bioreactor. Among individual strains, SH10 exhibited significantly higher potential to improve mangrove seedling's morphology, anatomy and growth during diesel treatment in rhizosphere compared to control. This was also evidenced by reduced activities and gene expression of antioxidant enzymes (catalases, peroxidases, ascorbic peroxidases, superoxide dismutases and polyphenol peroxidases) and lipid peroxidation during microbe-diesel interactions. Interestingly, we noticed significantly higher soil-enzyme activities (phosphatases and glucosidases) and essential metabolites in seedling's rhizosphere after bacteria and diesel treatments. Degradation of longer n-alkane chains in the rhizosphere also revealed a potential pathway that benefits mangroves by bacterial strains during diesel contaminations. Current results support microbes' application to rhizoengineer plant growth, responses, and phytoextraction abilities in environments contaminated with diesel spills. AVAILABILITY OF DATA AND MATERIALS: The datasets generated during the current study are available in the NCBI GenBank ((https://www.ncbi.nlm.nih.gov).

Effect of In Situ Bioremediation of Soil Contaminated with DDT and DDE by Stenotrophomonas sp. Strain DXZ9 and Ryegrass on Soil Microorganism

In the present study, the changes in the microbial populations, enzyme activity and bacterial community structure in contaminated soils were investigated during the bioremediation of using Stenotrophomonas sp. strain DXZ9 and ryegrass. The results showed that the removal rates were 81% for DDT and 55% for DDE (69% for DDTs) with ryegrass-microbe. Microbial activity was remarkably improved, and the number of bacteria increased sharply from 7.32 × 106 to 2.56 × 108 cells/g in the 10 days due to successful colonization of the strains and effects of the ryegrass rhizosphere. There was significant difference in fungi number with ryegrass when comparing the 30th and 90th days with the 210th day: The actinomycete number in the soil with ryegrass was higher than without ryegrass, and it indicated that the number of microorganisms significantly increased under the action of ryegrass. The activities of polyphenol oxidase, dehydrogenase and catalase were significantly activated by the combination of ryegrass and microbe, and urease activity was less affected: It has influence on the diversity of bacterial community structure in the soil, but its influence gradually decreased by denaturing gradient gel electrophoresis with an extension in time. The activities represented promising tools for decontaminating and restoring the ecosystem in sustainable ways, and proposing new approaches and technological bottlenecks to promote DDT biodegradation is very significant.

In situ phytoremediation of polycyclic aromatic hydrocarbon-contaminated agricultural greenhouse soil using celery

Although celery has been established as an effective plant in the remediation of organic pollutant-contaminated soil, few studies have investigated the associated biological processes in rhizosphere and the effect of celery on agricultural field remediation in situ. In this study, a polycyclic aromatic hydrocarbon (PAH)-contaminated agricultural greenhouse was used as the experimental site, and three celery species (Apium graveolens L., Oenanthe javanica (Blume) DC., Libanotis seseloides (Fisch. & C.A. Mey. ex Turcz.) Turcz.) were applied for in situ remediation. After 90 days, the PAH dissipation rate of the L. seseloides treatment was highest (50.21%), and most of the PAHs were limited to its roots (translocation factor 0.516). This suggested that L. seseloides is a potential species for phytoremediation coupled with agro-production. The culturable microbial population and invertase activity results strongly supported that O. javanica is suitable for the establishment of exogenous bacteria-celery co-remediation techniques. Pearson's correlation analysis showed that the polyphenol oxidase (PPO) activity was highly significantly positively correlated with the PAH dissipation rate (r = 0.984, P < 0.01), and we suggest that PPO can be used as a microecological index during PAH remediation.

In situ aerobic composting eliminates the toxicity of Ageratina adenophora to maize and converts it into a plant- and soil-friendly organic fertilizer

Ageratina adenophora has invaded many subtropical and tropical countries and caused tremendous ecological and economic losses. This necessitates a new way to use the debris left after clearing this plant. Therefore, the allelochemicals in fresh and aerobically composted A. adenophora plants (FA and CA, respectively) were compared, and their allelopathy against maize was evaluated. The results showed that CA decreased the allelochemicals (6-hydroxy-5-isopropyl-3,8-dimethyl-4a,5,6,7,8,8a-hexahydronaphthalen-2(1H)-one and 4,7-dimethyl-1-(propan-2-ylidene)-1,4,4a,8a-tetrahydronaphthalene-2,6(1H, 7H)-dione) by over 95% compared to FA. In a seed germination test, CA aqueous solutions improved the seed germination and seedling growth, whereas FA solutions led to opposite results. Chemical fertilizers (CF) plus FA resulted in much lower plant biomass and nutrient uptake than CF in a greenhouse experiment. Compared with CF, CF+CA showed positive effects on maize, soil microbial biomass and diversity and enzyme activities in the field. However, the compositions of the predominant microbes were almost unaffected by the application of CA and CF+CA. These significant findings extended our knowledge regarding the elimination of A. adenophora toxicity against other plants and soil microbes through allelochemical degradation in the composting process. In situ aerobic composting provides a new, simple and economical method to convert A. adenophora into a plant- and soil-friendly organic fertilizer.

Effect of lignin and plant growth-promoting bacteria (Staphylococcus pasteuri) on microbe-plant Co-remediation: A PAHs-DDTs Co-contaminated agricultural greenhouse study

Due to the ecological toxicity and environmental residues, how to remove the persistent organic pollutants (POPs), especially of polycyclic-aromatic-hydrocarbons (PAHs) and dichloro-diphenyl-trichloroethanes (DDTs), from agricultural soil has captured the attention of scholars for a long time. To develop an effective and low-cost in situ co-remediation technique, five independent but complementary treatments were used on an over-standard PAHs-DDTs co-contaminated soil in an agricultural greenhouse. Experimental results identified that the combination of microbe (Bacillus methylotrophicus) - plant (Brassica rapa) could remove rhamnolipid activated PAHs and DDTs effectively after enhanced by Staphylococcus pasteuri. Also, the Benzoapyrene and total DDTs residue in Brassica rapa was up to the standard of National (China) food safety. The lignin enhanced the removal of high-rings PAHs and p-p' DDE but reduced soil microbial biomass carbon and soil enzymes activity (polyphenol oxidase, invertase and acid phosphatase). Pearson correlation analysis showed that polyphenol oxidase activity was significantly related to the PAHs/DDTs dissipation rate. Our research suggested a new amendment that could remediate PAHs/DDTs co-contaminated agricultural soil without interrupting crop production, and the polyphenol oxidase activity should be considered as a micro-ecological indicator in this process.

The Role of Dactylis Glomerata and Diesel Oil in the Formation of Microbiome and Soil Enzyme Activity

The global demand for petroleum contributes to a significant increase in soil pollution with petroleum-based products that pose a severe risk not only to humans but also to plants and the soil microbiome. The increasing pollution of the natural environment urges the search for effective remediation methods. Considering the above, the objective of this study was to determine the usability of Dactylis glomerata for the degradation of hydrocarbons contained in diesel oil (DO), as well as the effects of both the plant tested and DO on the biochemical functionality and changes in the soil microbiome. The experiment was conducted in a greenhouse with non-polluted soil as well as soil polluted with DO and phytoremediated with Dactylis glomerata. Soil pollution with DO increased the numbers of microorganisms and soil enzymes and decreased the value of the ecophysiological diversity index of microorganisms. Besides, it contributed to changes in the bacterial structure at all taxonomic levels. DO was found to increase the abundance of Proteobacteria and to decrease that of Actinobacteria, Acidobacteria, Chloroflexi, Gemmatimonadetes and Firmicutes. In the non-polluted soil, the core microbiome was represented by Kaistobacter and Rhodoplanes, whereas in the DO-polluted soil, it was represented by Parvibaculum and Rhodococcus. In soil sown with Dactylis glomerata, gasoline fraction (C₆–C₁₂) degradation was higher by 17%; mineral oil (C₁₂–C₃₅), by 9%; benzene, by 31%; anthracene, by 12%; chrysene, by 38%; benzo(a)anthracene, by 19%; benzo(a)pyrene, by 17%; benzo(b)fluoranthene, by 15%; and benzo(k)fluoranthene, by 18% than in non-sowed soil. To conclude, Dactylis glomerata proved useful in degrading DO hydrocarbons and, therefore, may be recommended for the phytoremediation of soils polluted with petroleum-based products. It has been shown that the microbiological, biochemical and chemical tests are fast and sensitive in the diagnosis of soil contamination with petroleum products, and a combination of all these tests gives a reliable assessment of the state of soils.

Catabolic Activity and Structural Diversity of Bacterial Community in Soil Covered by Halophytic Vegetation

The catabolic activity and structural diversity of soil bacteria covered by five different halophytic vegetation types in the Yellow River Delta affected by long-term salinization were studied using Biolog-Eco technology. The result showed that soil quality, the diversity, and catabolic activity of the bacterial community of mildly salt-tolerant vegetation (Imperata cylindrical (L.) Beauv. and Apocynum venetum L.) were significantly higher than those of the bacterial community of highly salt-tolerant vegetation (Suaeda salsa (L.) Pall., Aeluropus sinensis (D.) Tzvel.), while these values were lowest for bacterial communities in bare land. The operational taxonomic units (OTUs) and diversity indexes of soil bacteria covered by Aeluropus sinensis were higher than those of soil bacteria covered by other types of vegetation, while those of soil bacteria covered by bare land were lowest. Principal component analysis (PCA) of the carbon source utilization capacity of the soil bacterial communities showed that organic acids, polymers, and amino acids were sensitive carbon sources that enabled study of the diversity of carbon metabolic functions in soil bacterial communities. And redundancy analysis (RDA) showed that D-galacturonic was significantly positively correlated with Verrucomicrobia, which further demonstrated the effect of organic acid carbon sources on metabolic functional diversity of soil bacterial communities in the Yellow River Delta.

Combination of rhamnolipid and biochar in assisting phytoremediation of petroleum hydrocarbon contaminated soil using Spartina anglica

Biochar (BC) and rhamnolipid (RL) is used in bioremediation of petroleum hydrocarbons, however, the combined effect of BC and RL in phytoremediation has not been studied until now. In this paper, the phytoremediation of petroleum hydrocarbon-contaminated soil using novel plant Spartina anglica was enhanced by the combination of biochar (BC) and rhamnolipid (RL). Samples of petroleum-contaminated soil (10, 30 and 50 g/kg) were amended by BC, BC+ RL and rhamnolipid modified biochar (RMB), respectively. After 60 day's cultivation, the removal rate of total petroleum hydrocarbons (TPHs) for unplanted soil (UP), planted soil (P), planted soil with BC addition (P-BC), planted soil with BC and RL addition (P-BC + RL) and planted soil with addition of RMB (P-RMB) were 8.6%, 19.1%, 27.7%, 32.4% and 35.1% in soil with TPHs concentration of 30 g/kg, respectively. Compared with UP, the plantation of Spartina anglica significantly decreased the concentration of C_8-14 and tricyclic PAHs. Furthermore, the application of BC and RMB alleviated the toxicity of petroleum hydrocarbons to Spartina anglica via improving plant growth with increasing plant height, root vitality and total chlorophyll content. High-throughput sequencing result indicated that rhizosphere microbial community of Spartina anglica was regulated by the application of BC and RMB, with increase of bacteria and plant mycorrhizal symbiotic fungus in biochar and RMB amended soil.

Effect of reclamation treatments on microbial activity and phytotoxicity of soil degraded by the sulphur mining industry

The aim of the work was to determine the trend, intensity and changes of selected microbial and phytotoxic parameters of degraded soil in the area of former sulphur mine reclaimed by post-flotation lime (PFL), sewage sludge (SS), mineral wool (MW- mixed with soil, MWP-pad) and mineral fertilizer (NPK). The following parameters: number of proteolytic bacteria and fungi, ammonification, nitrification, activities of alkaline phosphatase and arylsulphatase Lepidium sativum growth index (GI) and phenolic compounds were analysed in the soil in second and third year of the experiment. The addition of the SS separately or in combination with other remediation agents was found to be the most valuable for the number of microorganisms, intensification of nitrification process and enzymatic activities. In objects where other materials were added without sewage sludge, the inhibition of fungal growth as well as alkaline phosphatase and arylsulphatase activities was observed, however the inhibitory effect declined with time. The observed increase of GI shows the long-term, positive effect of treatments on soil properties concerning plant growth. The use of lime and lime together with sewage sludge contributed to the decrease in the content of phenolic compounds in the reclaimed soil.

Characterizing microbial diversity and community composition of groundwater in a salt-freshwater transition zone

A salt-freshwater transition zone due to seawater intrusion to groundwater promotes changes in microbial diversity and community composition in a coastal aquifer. The main purpose of this study is to explore the effect of seawater intrusion on the groundwater quality in a salt-freshwater transition zone and identify the microbial fingerprints of seawater intrusion. The changes in microbial community diversity response to the seawater intrusion were characterized by comparing the community structures of the microbes in fresh groundwater, seawater, and salty groundwater from various monitoring wells at different depths using the high throughput 16S rDNA gene sequencing. Results show that seawater had the lowest taxon richness and evenness, and the irrigation water had the highest richness and evenness. Statistical analysis showed that DO%, ORP, and Cl^- affected microbial distribution in the groundwater; while DO% was a main environmental factor influencing microbial community diversity. The analysis of microbial community structures indicates that the order Oceanospirillales and the family Alteromonadaceae could be used as indicators of seawater intrusion.

Effects of di-n-butyl phthalate on rhizosphere and non-rhizosphere soil microbial communities at different growing stages of wheat

The potential effects of dibutyl phthalate (DBP) on soil ecosystems and biological processes have recently aroused great concern because of the ubiquitous nature of this pollutant. However, the effects of DBP-associated disturbance on rhizosphere and non-rhizosphere soil microbial communities remain poorly understood. In the present study, we investigated the effects of DBP contamination on microbial function and soil enzyme activities in rhizosphere and non-rhizosphere soils throughout the growing season of wheat. We conducted pot experiments under glasshouse conditions and used different concentrations of DBP: 10, 20, and 40 mg kg^-1. We found that the average well color development value and McIntosh index in rhizosphere and non-rhizosphere soils increased in the 10 and 20 mg kg^-1 DBP treatments, but declined in the 40 mg kg^-1 DBP treatment at the seedling and tillering stages, particularly, in the non-rhizosphere soil. DBP addition enhanced the Shannon-Wiener and Simpson indexes in rhizosphere and non-rhizosphere soils throughout the growing period of wheat. A principal component analysis clearly differentiated the treatments from the control, indicating that DBP led to different patterns of potential carbon utilization in rhizosphere and non-rhizosphere soils. The microbial use of amino acids was significantly increased in rhizosphere and non-rhizosphere soils after DBP addition, while the use of carbohydrates was significantly declined (p < 0.05). The dehydrogenase, urease, and acid phosphatase activities were significantly stimulated (p < 0.05) at the seedling stage, while the phenol oxidase and β-glucosidase activities were inhibited. The 40 mg kg^-1 DBP treatment significantly decreased the phenol oxidase and β-glucosidase activities in rhizosphere and non-rhizosphere soils at the seedling stage, particularly in non-rhizosphere soil (p < 0.05). The microbial function and soil enzymatic activities were gradually restored following the wheat growing stage. These results offer a better understanding of the effects of DBP on the activities and functional diversity of microbial communities in farmland soils.

The effect of antibiotics on the persistence of herbicides in soil under the combined pollution

Antibiotic contamination in agricultural lands through manure application causes changes in soil enzyme activity and the abundance of microbes, which may affect the fate of agrochemicals. A clear understanding of antibiotic-pesticide interactions is very limited. The objective of this study was to investigate the effect of oxytetracycline (OTC) on the persistence of triazine and chloroacetanilide herbicides in soil under a combined application scenario. Soil enzyme activity and the abundance of soil microbes disturbed by OTC were measured. The results showed that OTC inhibited the dissipation of the herbicides and the effect depended on OTC concentration. For example, the half-lives of acetochlor increased from 6.9 days to 21.6 days with the presence of OTC at 50 mg/kg. It was also found the dissipation of the herbicides would still be affected after a month of OTC exposure at high concentration. Co-application also decreased activity of soil urease, dehydrogenase and catalase during earlier incubation periods, then recovered gradually. Furthermore, OTC reduced the abundance of fungi and bacteria, which might relate to inhibition of herbicide dissipation. Co-application of antibiotics and herbicides resulted in greater herbicide persistence, possibly increasing risk of environmental contamination.