Interactive effect of dissolved organic matter and phenanthrene on soil enzymatic activities

Biochar enhances Cd mineralization through microbially induced carbonate precipitation as a soil remediation strategy for rice paddies

Microbial induced carbonate precipitation (MICP) is a promising technique for remediating Cd-contaminated soils. However, the high cost and potential disruption to soil micro-ecology due to the excessive urea addition remain significant challenges, limiting the broader application of MICP technology in agricultural soils. This study aims to improve the efficiency of Cd immobilization by MICP under low urea levels by investigating the stimulatory effect of porous materials on urease secretion by ureolytic bacteria. Results demonstrate that these materials, including biochar, activated carbon, zeolite, and oyster shell, can stimulate the growth of ureolytic bacteria strain kp-22, but not diatomite. Urease activity was greatly improved within 12 h, and the Cd removal rate reached over 82.12% within 0.5 h. Notably, biochar supported urealytic bacterium strain kp-22 (BCM) can steadily remove Cd in solution, with the Cd removal rate remaining close to 99% even after multiple additions of Cd. XRD analysis shows that Cd was removed by BCM due to the formation of CdCO3. Soil experiment reveals that BCM significantly decreased the bioavailable Cd content in both flooded and unflooded paddy soils, even when the urea addition was at a dosage suitable for agricultural production. 16S rRNA gene sequencing shows that the disturbance caused by BCM to the soil bacterial community was lower than that caused by strain kp-22 alone. These findings offer new insights into enhancing the efficiency of MICP for Cd remediation, increasing the potential for broader application of MICP technology in sustainable agriculture.

Comprehensive bioremediation effect of phosphorus-mineralized bacterium Enterobacter sp. PMB-5 on cadmium contaminated soil-crop system

Phosphate-mineralizing bacteria (PMBs) have been widely studied by inducing phosphate heavy metal precipitation, but current researches neglect to study their effects on soil-microbe-crop systems on cadmium (Cd) contaminated. Based on this, a strain PMB, Enterobacter sp. PMB-5, was inoculated into Cd contaminated pots to detect soil characteristics, Cd occurrence forms, soil biological activities, plant physiological and biochemical indicators. The results showed that the inoculation of strain PMB-5 significantly increased the available phosphorus content (85.97%-138.64%), Cd-residual fraction (11.04%-29.73%), soil enzyme activities (31.94%-304.63%), plant biomass (6.10%-59.81%), while decreased the state of Cd-HOAc (11.50%-31.17%) and plant bioconcentration factor (23.76%-44.24%). These findings indicated that strain PMB-5 could perform the function of phosphorus solubilization to realize the immobilization of Cd in the complex soil environment. Moreover, SEM-EDS, FTIR, XPS, and XRD analysis revealed that strain PMB-5 does not significantly alter the soil morphology, structure, elemental distribution, and chemical composition, which suggested that remediation of Cd contamination using strain PMB-5 would not further burden the soil. This research implies that PMB-5 could be a safe and effective bioinoculant for remediating Cd-contaminated soils, contributing to the sustainable management of soil health in contaminated environments.

Enhanced Cd activation by Coprinus comatus endophyte Bacillus thuringiensis and the molecular mechanism

Fungal endophytes not only tolerate and activate Cd in soil but also promote host growth, yet its Cd activation capacity and mechanism remain unrevealed. Our previous study isolated a robust endophyte Bacillus thuringiensis L1 from Coprinus comatus fruiting body with splendid Cd resistance and activation abilities under laboratory conditions. In this study, those peculiarities were investigated in the actual soil environment. L1 could significantly increase the soil bioavailable Cd content and effectively compensate for alkali-hydro nitrogen losses and microbial inhibition caused by Cd. Furthermore, L1 inoculation improved the soil's bacterial community structure and increased the relative abundance of Cd-resistant bacteria, such as Actinobacteria, Chloroflexi, Acidobacter, and Firmicutes, closely associated with the soil enzyme activity shift. The genome sequencing analysis revealed the presence of genes related to growth promotion, resistance to Cd stress, and Cd activation, which were significantly up-regulated under Cd stress. Notably, L1 mainly activates Cd in soil by secreting citric acid, succinic acid, siderophore, and soluble phosphorus substances to chelate with Cd or dissolve bounded Cd. Meanwhile, the metal-responsive transcription repressor (CadC) and the Cd-translocating protein P-type ATPase (CadA) can help the L1 to suppress the toxicity of Cd. Those results help to unveil the possible mechanism of L1 in Cd-contaminated soil remediation, providing a clear strategy for Cd bio-extraction from soil.

Assessment of soil property in the Guyuan region from Ningxia Province of China and prediction of pepper blight

Soil quality is an important determinant of soil-use efficiency in the Loess Plateau. However, there is no in-depth study on the soil quality of the Loess Plateau. The present study compared the quality of the 0-20 cm soil layer (T0-20) and the 20-40 cm soil layer (T20-40) from the Guyuan region located in the Loess Plateau. The analysis revealed that T0-20 had a higher content of total N, total P, available P, and organic matter, and the activities of microbial enzymes, especially β-grape-glycosidase (β-GC) and sucrase (SC), than T20-40, indicating that soil quality in T0-20 was better than T20-40. Amplicon sequencing found that Pseudombrophila from Ascomycota was the most abundant microbial species and significantly differed between T0-20 (34.2%) and T20-40 (48.7%). This species and another 19 microbial species, such as Ceratobasidiaceae and Mortierellaceae, determined the diversity of soil microorganism. Further analysis of the phenotype and other parameters of pepper seedlings subjected to P. capsici infection isolated from test soil revealed that decreased organic matter content in deep soil layer is related to happening of pepper blight, and 3 h after infection was the critical time point for infection. The peroxidase (POD) activity increased after P. capsici infection and was positively correlated with infection time, suggesting this enzyme may be an indicator of pepper blight occurrence. These findings provide a theoretical foundation for planning pepper blight management and crop cultivation strategies in the Guyuan region.

Enhancement of electrokinetic-phytoremediation by Ophiopogon japonicus: stimulation of electrokinetic on root system and improvement of polycyclic aromatic hydrocarbon degradation

Root systems are sensitive to voltage and tend to improve the degradation of organic pollutants by promoting the root exudates and increasing microbial enzyme activity in the rhizosphere under the effect of electrokinetic. In this study, electrokinetic-assisted phytoremediation (EKPR) was applied for the remediation of soil containing phenanthrene (PHE) and pyrene (PYR). Direct current (DC) voltage (1 V cm-1) was applied across the soils for 30 days following 3 treatment schedules (0 h, 4 h, and 12 h per day), referred to as treatments EK0, EK4, and EK12. Electrokinetic assistance improved phytoremediation. Compared to EK0, the removal of PHE and PYR increased by 51.79% and 45.07% for EK4 and by 43.18% and 38.75% for EK12. The applied voltage promoted root growth, stimulated the root exudate release, and increased accumulation of PHE and PYR by plants, and the effect was most pronounced in treatment EK4. Catalase and urease activities in rhizosphere soil also increased, by respective increments of 44.51% and 40.86% for EK4 and by 28.53% and 21.24% for EK12. In this study, we demonstrated that a low voltage applied for an appropriate duration (4 h per day) improves removal of PAHs by stimulating root growth, promoting the root exudate release and enhancing enzyme activity in the microbiome of rhizosphere soil.

Simulation of Biophysicochemical Characteristics of the Soils Using Geoelectrical Measurements near the Sewage Station, Assiut City, Egypt

Numerous farmers regularly irrigate their farms with inadequately treated sewage water pumped from the sewage system in the Arab El-Madabegh district of Assiut City, Egypt. According to previous studies, long-term irrigation with partially treated sewage water resulted in significant changes in the physicochemical properties of soil. The principal goals of this study are (1) to infer empirical equations between geoelectrical resistivity measurements and certain biophysicochemical parameters of some soil samples, and (2) to use these empirical equations to calculate the biophysicochemical parameters of the unknown samples for the same location. For this purpose, 27 soil samples at different depth levels (0 to 25, 25 to 60, and 60 to 90 cm) were collected from eleven locations at the sewage station. Physical properties including water content and particle size distribution, chemical properties including soil pH, electrical conductivity (EC), and the heavy metals concentrations, biological properties including total coliform counts, and geoelectrical resistivity measurements were estimated and analyzed for these samples. Electrical resistivity measurements and biophysicochemical properties were cross-correlated using the exponential trend line to fit the cross-correlated data, and the empirical relationships were obtained. These empirical relationships in conjunction with the measured electrical resistivity measurements were used to calculate the biophysicochemical values of the other three random soil samples. The biophysicochemical values of the former three samples were measured by the same normal procedures as 27 samples. Then, the calculated values were correlated with the measured ones. Good correlations between the estimated and the measured values for biophysicochemical features were obtained. Therefore, this method can be employed to calculate the biophysicochemical parameters for any unknown samples that have the same geological conditions for estimating and monitoring soil contamination.

Effects of different carbon substrates on PAHs fractions and microbial community changes in PAHs-contaminated soils

Different types of carbon substrates were widely used in soil remediation. However, differences of their impacts and related mechanisms on degradation of polycyclic aromatic hydrocarbons (PAHs) and microbial community structures in contaminated soil still remain unclear. Here, we investigated the effects of corn straw (S), glucose (G), straw combined with glucose (SG), and sodium azide (N, as an abiotic control) on PAHs fractions and bacterial communities in soil. After 70 days' microcosm experiments, total PAHs concentrations were significantly reduced by 30.9%, 19.5% and 44.6% under S, G and SG treatments. Water soluble, acid soluble and residual PAHs under all treatments were significantly decreased after 70 days of incubation, while organically bound PAHs were increased by 11.4%, 22.7% and 36.1% under G, S and SG treatments. Additionally, straw and glucose application increased relative abundance related PAHs-degrading bacteria and the copy numbers of gram-negative (PAHs-RHDα GN) and gram-positive genes (PAHs-RHDα GP) in the contaminated soil. Redundancy analysis (RDA) and Random Forest (RF) indicated that PAHs fractions are crucial factors for biodegradation of PAHs in PAHs-contaminated soils amended with carbon substrates. These suggested that carbon substrates contributed to PAHs conversion from residual PAHs (nonlabile fractions) to organically bound PAHs and thus increased the potential for PAHs conversion to water-soluble and organic acid-soluble PAHs, which were more easy to be utilized by soil microorganisms. This study revealed the new insights of different carbon substrates on degradation and dynamic changes of PAHs fractions and the better potential of combined application of straw and glucose in enhancing degradation of PAHs in PAHs-contaminated soils.

Ecological risk assessment of priority PAHs pollutants in crude oil contaminated soil and its impacts on soil biological properties

Polycyclic aromatic hydrocarbons (PAHs) are one of the major toxic constituents of crude oil and therefore, an understanding on PAHs associated risks and their relationship with soil biological parameters are necessary for adopting effective risk-based and site specific remediation strategies in the contaminated soil. Here, risks evaluation of eight detected PAHs in terms of toxic equivalent concentration (TEQ_C), benzo(a)pyrene equivalent (BaPeq), contamination factor (CF), pollution load index (PLI), hazard quotient (HQ), hazard index (HI), toxic unit for individual PAHs (TU) and PAHs mixture (TU_m) have been evaluated. Besides, the effect of PAHs contamination on soil biological properties has also been investigated and correlated with PAHs concentrations. The TEQc of eight PAHs was recorded in the range of 0.06-5.0 mg kg^-1 soil_, whereas the BaPeq value was 25.3 mg kg^-1 soil which exceed the permissible limit. Similarly, CF (85.5-1668.2), PLI (322.8), HQ (311.7-8340.9), HI (26,443.8), TU (227.9-3821.6) and TU_m(7916.2) also exceed the permissible values for non-toxic conditions indicating carcinogenic risk for humans. Besides, activities of soil dehydrogenase, urease, alkaline-phosphatase, catalase, amylase and cellulase were decreased by 1.5-2.3 folds in the contaminated soil than control. The results of Pearson's correlation matrix also established negative impact of PAHs on the soil's biological properties.

Bacteria and Soil Enzymes Supporting the Valorization of Forested Soils

To decompose forest biomass, microorganisms use specific enzymes from the class of oxidoreductases and hydrolases, which are produced by bacteria and soil fungi. In post-agricultural forest soils, bacteria adapt more easily to changing ecological conditions than fungi. The unique features of bacteria, i.e., tolerance and the ability to degrade a wide range of chemical compounds, prompted us to conduct research that contributes to the improvement of the broadly understood circular management of biomass production and economic efficiency. This study aimed to analyze changes in the microbiological activity and the activities of dehydrogenases, catalase, β-glucosidase, urease, arylsulfatase, acid phosphatase, and alkaline phosphatase in the soil sampled from under Picea abies (Pa), Pinus sylvestris (Ps), Larix decidua (Ld), Quercus robur (Qr), and Betula pendula (Bp), after 19 years. The control object was unforested soil. The studies allowed one to demonstrate the relationship between the activity of soil enzymes and the assemblages of culturable microorganisms and bacteria determined by the metagenomic method and tree species. Thus, it is possible to design the selection of tree species catalyzing enzymatic processes in soil. The strongest growth promoter of microorganisms turned out to be Quercus robur L., followed by Picea abies L., whereas the weakest promoters appeared to be Pinus sylvestris L. and Larix decidua M.

Bioprospecting of indigenous biosurfactant-producing oleophilic bacteria for green remediation: an eco-sustainable approach for the management of petroleum contaminated soil

In the present study, the efficiency of four different strains of Pseudomonas aeruginosa and their biosurfactants in the bioremediation process were investigated. The strains were found to be capable of metabolizing a wide range of hydrocarbons (HCs) with preference for high molecular weight aliphatic (ALP) over aromatic (ARO) compounds. After treating with individual bacteria and 11 different consortia, the residual crude oils were quantified and qualitatively analyzed. The bacterial strains degraded ALP, ARO, and nitrogen, sulphur, oxygen (NSO) containing fractions of the crude oil by 73-67.5, 31.8-12.3 and 14.7-7.3%, respectively. Additionally, the viscosity of the residual crude oil reduced from 48.7 to 34.6-39 mPa s. Further, consortium designated as 7 and 11 improved the degradation of ALP, ARO, and NSO HCs portions by 80.4-78.6, 42.7-42.4 and 21.6-19.2%, respectively. Moreover, addition of biosurfactant further increased the degradation performance of consortia by 81.6-80.7, 43.8-42.6 and 22.5-20.7%, respectively. Gas chromatographic analysis confirmed the ability of the individual strains and their consortium to degrade various fractions of crude oil. Experiments with biosurfactants revealed that polyaromatic hydrocarbons (PAHs) are more soluble in the presence of biosurfactants. Phenanthrene had the highest solubility among the tested PAHs, which further increased as biosurfactant doses raised above their respective critical micelle concentrations (CMC). Furthermore, biosurfactants were able to recover 73.5-63.4% of residual oil from the sludge within their respective CMCs. Hence, selected surfactant-producing bacteria and their consortium could be useful in developing a greener and eco-sustainable way for removing crude oil pollutants from soil.

Effects of Fe-Mn impregnated biochar on enzymatic activity and bacterial community in phthalate-polluted brown soil planted with wheat

A pot experiment was carried out on brown soil polluted by dibutyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) to investigate the effects of biochar (BC) derived from corn straw and Fe-Mn oxide modified biochar composites (FMBC) on the bioavailability of DBP and DEHP, as well as ecosystem responses in rhizosphere soil after wheat ripening. The results indicate that the application of BC and FMBC significantly increases soil organic matter, pH, available nitrogen (AN), Olsen phosphorus, and available potassium (AK); reduces the bioavailability of DBP and DEHP; enhances the activities of dehydrogenase, urease, protease, β-glucosidase, and polyphenol oxidase; and decreases acid phosphatase activity. No changes in richness and diversity, which were measured by Illumina MiSeq sequencing, were observed following BC and FMBC application. The bacterial community structure and composition varied with DBP/DEHP concentrations and BC/FMBC additions in a nonsystematic way and no significant trends were observed. In addition, FMBC exhibited better performance in increasing soil properties and decreasing the bioavailability of DBP and DEHP compared with BC. Hence, the FMBC amendment may be a promising way of developing sustainable agricultural environmental management.

Phytotoxicity of petroleum hydrocarbons: Sources, impacts and remediation strategies

Extraction and exploration of petroleum hydrocarbons (PHs) to satisfy the rising world population's fossil fuel demand is playing havoc with human beings and other life forms by contaminating the ecosystem, particularly the soil. In the current review, we highlighted the sources of PHs contamination, factors affecting the PHs accumulation in soil, mechanisms of uptake, translocation and potential toxic effects of PHs on plants. In plants, PHs reduce the seed germination andnutrients translocation, and induce oxidative stress, disturb the plant metabolic activity and inhibit the plant physiology and morphology that ultimately reduce plant yield. Moreover, the defense strategy in plants to mitigate the PHs toxicity and other potential remediation techniques, including the use of organic manure, compost, plant hormones, and biochar, and application of microbe-assisted remediation, and phytoremediation are also discussed in the current review. These remediation strategies not only help to remediate PHs pollutionin the soil rhizosphere but also enhance the morphological and physiological attributes of plant and results to improve crop yield under PHs contaminated soils. This review aims to provide significant information on ecological importance of PHs stress in various interdisciplinary investigations and critical remediation techniques to mitigate the contamination of PHs in agricultural soils.

Impacts and tolerance responses of Coprinus comatus and Pleurotus cornucopiae on cadmium contaminated soil

Large amounts of cadmium (Cd) have been discharged into soil with the rapid development of industry. In this study, we revealed the impacts of Coprinus comatus (C. comatus) and Pleurotus cornucopiae (P. cornucopiae) on soil and the tolerance responses of macrofungi in the presence of Cd by the analysis of soil biochemical properties and macrofungi growth indexes. Results showed that with the cultivation of C. comatus and P. cornucopiae, the HOAc-extractable Cd in soil individually reduced by 9.53% and 11.35%, the activities of soil urease, acid phosphatase, dehydrogenase, and Fluorescein diacetate (FDA) hydrolysis increased by 18.11-101.45%, 8.39-18.24%, 9.37-55.50% and 28.94-41.92%, respectively. Meanwhile, different soil bacterial communities were observed with various macrofungi cultivations. Also, Cd accumulation significantly enhanced the macrofungi antioxidant enzyme activities, which increased by 24.10-45.43%, 30.11-61.53% and 7.03-26.81% for catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities in the macrofungi, respectively. Moreover, the enhanced macrofungi endophytic bacterial diversities with Cd existence was firstly observed in the present experiment. These findings revealed the possible Cd resistance mechanisms in macrofungi, suggesting C. comatus and P. cornucopiae were promising ameliorators for Cd contaminated soil.

Impact of Various Grass Species on Soil Bacteriobiome

Today, various grass species are important not only in animal feeding but, increasingly often, also in energetics and, due to esthetic and cultural values, in landscape architecture. Therefore, it is essential to establish the roles various grass species and their functional forms play in modifying soil bacteriobiome and enzymatic activity. To this end, a pot experiment was conducted to examine effects of various fodder grass and lawn grass species on the bacteriobiome and biochemical properties of soil. Nonsown soil served as the control for data interpretation. Analyses were carried out with standard and metagenomic methods. The intensity of effects elicited by grasses depended on both their species and functional form. More favorable living conditions promoting the development of soil bacteria and, thereby, enzymatic activity were offered by fodder than by lawn grass species. Among the fodder grasses, the greatest bacteriobiome diversity was caused by sowing the soil with Phleum pratense (Pp), whereas among lawn grasses in the soil sown with Poa pratensis (Pr). Among the fodder grasses, the highest enzymatic activity was determined in the soil sown with Lolium x hybridum Hausskn (Lh), and among the lawn grasses—in the soil sown with Lolium perenne. Sowing the soil with grasses caused the succession of a population of bacterial communities from r strategy to k strategy.

Effects of Elevated Ozone Concentrations on Root Characteristics and Soil Properties of Elaeocarpus sylvestris and Michelia chapensis

The increasing concentration of surface ozone (O₃) was observed during recent decades in the world, which affects tree roots and forest soils. Meanwhile, the impact of ozone on tree roots is greatly affected by soil condition. However, there is a lack of knowledge about the possible effects of ozone on tree roots and soil processes. In this study, The influences of surface ozone (O₃) stress on the root biomass, morphology, nutrients, soil properties, and soil enzyme activity of Elaeocarpus sylvestris and Michelia chapensis seedlings were examined at four O₃ concentrations (charcoal-filtered air, 1 × O₃ air, 2 × O₃ air, and 4 × O₃ air). Elevated O₃ concentrations were found to significantly increase the root C content, N content, C/P ratio, and N/P ratio, and significantly decrease the root biomass, number of root tips, and root C/N ratio of both species. The soil organic matter content, pH, total N content, and urease and catalase activities of both species tended to increase. The limitation in root growth and responses in the root structure of E. sylvestris induced by elevated O₃ concentrations led to increased bulk density and decreased soil porosity and void ratio. These profound effects of O₃ concentrations on the roots and soil characteristics of these two species underscore the importance of research in O₃ science.

Characteristics and in situ remediation effects of heavy metal immobilizing bacteria on cadmium and nickel co-contaminated soil

Cadmium (Cd) and nickel (Ni) in soil have caused serious environmental problems and increased healthy risks to humans and biota, it is vital important and necessary to develop effective methods to resolve the combined contaminated problems. In this study, strains L5 and L6 with good heavy metal resistant and immobilizing capacities were isolated from Cd and Ni contaminated soil. Bacterial characteristic experiment illustrated that many functional groups (-OH, -NH₂ and -COO et al.) were distributed on the surface of L5 and L6. Under the stress of heavy metals, bacterial appearances were distorted. The pot experiment indicated that the concentrations of HOAc-extractable Cd and Ni in soil reduced 6.26-15.33% and 13.31-19.53% with the inoculation of L5 and L6. In addition, the immobilization rates on Cd and Ni improved 61.27-128.50% and 23.69-39.66% with re-inoculation of strains L5 and L6 at 30 days, respectively. After inoculation of strains L5 and L6 for 60 days, the activities of FDA hydrolysis, acid phosphatase, urease, invertase and dehydrogenase in soil increased obviously. Furthermore, bacterial diversity indexes and community structure of soil were also improved. Thus, given the beneficial remediation effects of the isolated strains, L5 and L6 have great potentials for heavy metals contaminated soil remediation.

Enhanced phytoremediation of PAHs-contaminated soil from an industrial relocation site by Ochrobactrum sp

Nowadays, the remediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil has received wide attention. In this work, Ochrobactrum sp. (PW) was isolated through selective enrichment from PAHs-contaminated soil in coking plant of Beijing, and the effects of PW on phytoremediation of that soil by alfalfa (Medicago sativa L.) and ryegrass (Lolium multiflorum Lam.) were investigated through pot experiments. Plant biomass, peroxidase (POD) activity, malondialdehyde (MDA) contents, soil enzyme activity (polyphenol oxidase and dehydrogenase activity), and residual concentration of PAHs in soils were determined to illustrate the ability of PW for enhancing the degradation of PAHs by plants. The results showed that the fresh weight of ryegrass and alfalfa inoculated with PW was significantly (p < 0.05) increased while the activity of POD and MDA contents were notably (p < 0.05) reduced than that without inoculation. Additionally, PW enhanced the activity of polyphenol oxidase and dehydrogenase in soil significantly (p < 0.05), and further enhanced the degradability of the system to PAHs. Different treatment methods could be ranked by the following order according to the degradability: SP (alfalfa + PW) > RP (ryegrass + PW) > PW (PW) > S (alfalfa) > R (ryegrass). The combined action of PW and alfalfa/ryegrass could accelerate the degradability of PAHs from soil contaminated by coking plants. PW could be used as potential bacteria to promote phytoremediation of the soil contaminated by PAHs.

Elucidation of the mechanisms into effects of organic acids on soil fertility, cadmium speciation and ecotoxicity in contaminated soil

The remediation effect of organic acids in heavy metal contaminated soil was widely studied. However, the comprehensive evaluation of organic acids on micro-ecological environment in heavy metal contaminated soil was less known. Herein, this experiment was conducted to investigate the impact of malic acid, citric acid and oxalic acid on soil fertility, cadmium (Cd) speciation and ecotoxicity in contaminated soil. Especially, to evaluate the ecotoxicity of Cd, high-throughput sequencing was used to investigate the soil bacterial community structure and diversity after incubation with organic acids. The results showed that obvious changes in soil pH were not observed. Whereas, the contents of available phosphorus (Olsen-P) and alkali hydrolysable nitrogen (Alkeline-N) evidently increased with a significant difference. Furthermore, compared to control, the proportion of acetic acid-extractable Cd increased by 3.06-6.63%, 6.11-9.43% and 1.91-6.22% respectively in the groups amended with malic acid, citric acid and oxalic acid, which indicated that citric acid did better in improving the availability of Cd than malic acid and oxalic acid. In terms of biological properties, citric acid did best in bacteria count increase, enzyme activities and bacterial community structure improvement. Accordingly, these results provided a better understanding for the influence of organic acids on the micro-ecological environment in Cd contaminated soil, based on physicochemical and biological analysis.

Vermicompost and biochar as bio-conditioners to immobilize heavy metal and improve soil fertility on cadmium contaminated soil under acid rain stress

This experiment was conducted to investigate the remediation effects of bio-conditioners vermicompost (VC) and biochar (BC) on cadmium contaminated soil under the threat of acid rain, individually and associatively. With the application of soil conditioners, the percentages of HOAc-extractable Cd decreased 5.2-6.8%, 9.0-13.5% and 7.9-12.1% in the groups amended with VC, BC and VC combined BC, respectively. When the pH of rain decreased from 7.0 to 4.0, the activity of acid phosphatase decreased 2.0%, 12.3%, 3.2%, 14.8% in VC, BC, VC combined BC and control groups, individually. This study affirmed that with the application of soil conditioners, the threat of heavy metal along with bioavailability of Cd was depressed, and the properties of soil biochemical indictors were enhanced. Oppositely, the bioavailability of Cd was promoted, and soil microbial viability as well as nutrient contents was inhibited with the spraying of acid rain. The findings indicated that acid deposition played a restrain effect on soil remediation process. Meanwhile, soil conditioners showed potentials to improve soil fertilities and alleviate the stress of acid rain.

Resistance of aerobic microorganisms and soil enzyme response to soil contamination with Ekodiesel Ultra fuel

This study determined the susceptibility of cultured soil microorganisms to the effects of Ekodiesel Ultra fuel (DO), to the enzymatic activity of soil and to soil contamination with PAHs. Studies into the effects of any type of oil products on reactions taking place in soil are necessary as particular fuels not only differ in the chemical composition of oil products but also in the composition of various fuel improvers and antimicrobial fuel additives. The subjects of the study included loamy sand and sandy loam which, in their natural state, have been classified into the soil subtype 3.1.1 Endocalcaric Cambisols. The soil was contaminated with the DO in amounts of 0, 5 and 10 cm³ kg^-1. Differences were noted in the resistance of particular groups or genera of microorganisms to DO contamination in loamy sand (LS) and sandy loam (SL). In loamy sand and sandy loam, the most resistant microorganisms were oligotrophic spore-forming bacteria. The resistance of microorganisms to DO contamination was greater in LS than in SL. It decreased with the duration of exposure of microorganisms to the effects of DO. The factor of impact (IF_DO) on the activity of particular enzymes varied. For dehydrogenases, urease, arylsulphatase and β-glucosidase, it had negative values, while for catalase, it had positive values and was close to 0 for acid phosphatase and alkaline phosphatase. However, in both soils, the noted index of biochemical activity of soil (BA) decreased with the increase in DO contamination. In addition, a positive correlation occurred between the degree of soil contamination and its PAH content.

Effects of dissolved organic matter derived from forest leaf litter on biodegradation of phenanthrene in aqueous phase

Dissolved organic matter (DOM) released from forest leaf litter is potentially effective for the degradation of polycyclic aromatic hydrocarbons (PAHs), yet the inherent mechanism remains insufficiently elucidated. In this study, we investigated the effects of DOM derived from Pinus elliottii and Schima superba leaf litter on the degradation of phenanthrene by the phenanthrene degrading bacterium Sphingobium sp. Phe-1. DOM from different origins and at a large range of concentrations enhanced the degradation rate of phenanthrene. DOM derived from P. elliottii leaf litter decomposed for 12 months used at a concentration of 100mg/L yielded the highest degradation rate (16.9% in 36h) and shortened the degradation time from 48h to 24h. Changes in the composition of DOM during degradation as measured by EEMs-FRI showed that proteins and tyrosine in the DOM supplied readily available nutrients that stimulated biological activity of Phe-1, increasing its growth rate and catechol 2,3-dioxygenase activity. Simultaneously, fulvic acid and humic acid in the DOM enhanced phenanthrene bioavailability by increasing the solubility and mass transfer of phenanthrene, enhancing the uptake kinetics of Phe-1, and increasing the bacteria's direct access to DOM-associated phenanthrene. Humic acid was co-metabolized by Phe-1, resulting in further stimulation of phenanthrene degradation.

Toxic effect of two kinds of mineral collectors on soil microbial richness and activity: analysis by microcalorimetry, microbial count, and enzyme activity assay

Flotation reagents are hugely and increasingly used in mining and other industrial and economic activities from which an important part is discharged into the environment. China could be the most affected country by the resulting pollution. However, their ecotoxicological dimension is still less addressed and understood. This study aimed to analyze the toxic effect of sodium isobutyl xanthate (SIBX) and sodium isopropyl xanthate (SIPX) to soil microbial richness and activity and to make a comparison between the two compounds in regard to their effects on soil microbial and enzymes activities. Different methods, including microcalorimetry, viable cell counts, cell density, and catalase and fluorescein diacetate (FDA) hydrololase activities measurement, were applied. The two chemicals exhibited a significant inhibitory effect (P < 0.05 or P < 0.01) to all parameters, SIPX being more adverse than SIBX. As the doses of SIBX and SIPX increased from 5 to 300 μg g^-1 soil, their inhibitory ratio ranged from 4.84 to 45.16 % and from 16.13 to 69.68 %, respectively. All parameters fluctuated with the incubation time (10-day period). FDA hydrolysis was more directly affected but was relatively more resilient than catalase activity. Potential changes of those chemicals in the experimental media and complementarity between experimental techniques were justified.

Mineralization of pyrene induced by interaction between Ochrobactrum sp. PW and ryegrass in spiked soil

This study was conducted to investigate the capability of pyrene-degrading bacterium Ochrobactrum sp. PW and ryegrass (Lolium multiflorum) grown alone and in combination on the degradation of pyrene in soil. After 60 days of ryegrass growth, plant biomass, pyrene-degrading microbial mass, soil enzyme activity (catalase activity and polyphenol oxidase activity) and residual concentration of pyrene in soils were determined. Higher dissipation rates were observed in PW inoculation treatments: ryegrass+PW rhizosphere soil (RP-r) and ryegrass+PW non-rhizosphere soil (RP-nr), than planting of ryegrass alone, rhizosphere (R-r) or non-rhizosphere (R-nr). The inoculation with PW significantly (p<0.05) increased the dry weight of ryegrass root and shoot, nearly 2.8 and 3.3 times higher than ryegrass treatment. The pyrene-degrading microbial mass indicated that a much larger mass of bacteria, actinobacteria were present in RP treatment. The catalase activity in all different treatments were significantly (p<0.05) higher than in with treatment R-nr, and the polyphenol oxidase activity was also significantly (p<0.05) increased by inoculation with PW, leading to enhanced mineralization of pyrene from soil. Our results suggest that adding of PAHs-degrading bacteria to soil can enhance remediation of PAHs contaminated soil, while improving plant growth.

Combined remediation of pyrene-contaminated soil with a coupled system of persulfate oxidation and phytoremediation with ryegrass

The in situ chemical oxidation technology (ISCO) and phytoremediation for PAHs have been studied respectively, but few focus on the feasibility of combining persulfate with ryegrass. This literature revealed the effect of persulfate oxidation on the growth of ryegrass and the removal ratios of pyrene in the couple system of persulfate oxidation and phytoremediation. The results demonstrated that half of pyrene in test soil was oxidized by persulfate in 7 days and then the residual pyrene concentration was decreased to a lower level by ryegrass in the following 2 months in oxidation treatment and drip washing and plants (OWP) and oxidation treatment and drip washing and plants and fertilization (OWFP) treatment. Ryegrass could grow well after persulfate oxidation with the oxidized soil washed by water. Ryegrass in OWP and OWFP treatments had higher ratios of overground and underground biomass. However, the seeds of ryegrass cannot germinate when drip washing was omitted. Pyrene together with residual persulfate changed soil enzyme activities. Drip washing and the growth of ryegrass made soil enzyme activities tend to returned to normal levels. Persulfate oxidation and phytoremediation were compatible to make contributions to the dissipation of pyrene. Persulfate oxidation activated by heat had higher removal efficiency of PAHs and phytoremediation could further decrease the pyrene concentration in spiked soil.

Temporal and spatial variations of contaminant removal, enzyme activities, and microbial community structure in a pilot horizontal subsurface flow constructed wetland purifying industrial runoff

A pilot-scale horizontal subsurface flow constructed wetland (HSSFCW) was operated to purify industrial runoff containing polycyclic aromatic hydrocarbons (PAHs) in Guangzhou, China. Synthetic industrial runoff was fed into the HSSFCW with continuous flow at an average loading rate of 0.128 m(3)/(m(2)/day) for about 2 years. Pollutants such as chemical oxygen demand (COD), total phosphorus (TP), and phenanthrene were mainly removed in the front quarter of the HSSFCW, and in the vertical direction, the average removal rates of COD, TP, total nitrogen (TN), ammonia, and phenanthrene of the upper layer were 64.23, 71.16, 50.81, 65.38, and 92.47 %, which were 1.23, 2.08, 1.48, 1.72, and 1.17 times higher than those of the bottom, respectively. Correlations among pollutant removal, soil environmental indexes, enzyme activities, and soil microbial community structure were evaluated. Enzyme assays (dehydrogenase, catalase, nitrate reductase, and polyphenol oxidase) showed significant associations between enzyme activities and pollutant removal (p < 0.01 and p < 0.05). Soil microbial community structure was assessed with denaturing gradient gel electrophoresis (DGGE) fingerprinting method, and results demonstrated that bacterial communities remained relatively stable in different seasons. Proteobacteria and Bacteroidetes were found to be the dominant phyla of the bacteria communities, and three clones which might be related to the biodegradation of phenanthrene were also detected. Results of the present work would broaden the knowledge of the purification mechanism of contaminants in the constructed wetlands (CWs), and identification of the treatment performances and temporal and spatial variations of biological activities of subsurface flow constructed wetlands (SSFCWs) would help to improve the operations of CWs for surface water protection.

Effect of alternating bioremediation and electrokinetics on the remediation of n-hexadecane-contaminated soil

This study demonstrated the highly efficient degradation of n-hexadecane in soil, realized by alternating bioremediation and electrokinetic technologies. Using an alternating technology instead of simultaneous application prevented competition between the processes that would lower their efficiency. For the consumption of the soil dissolved organic matter (DOM) necessary for bioremediation by electrokinetics, bioremediation was performed first. Because of the utilization and loss of the DOM and water-soluble ions by the microbial and electrokinetic processes, respectively, both of them were supplemented to provide a basic carbon resource, maintain a high electrical conductivity and produce a uniform distribution of ions. The moisture and bacteria were also supplemented. The optimal DOM supplement (20.5 mg·kg⁻¹ glucose; 80–90% of the total natural DOM content in the soil) was calculated to avoid competitive effects (between the DOM and n-hexadecane) and to prevent nutritional deficiency. The replenishment of the water-soluble ions maintained their content equal to their initial concentrations. The degradation rate of n-hexadecane was only 167.0 mg·kg⁻¹·d⁻¹ (1.9%, w/w) for the first 9 days in the treatments with bioremediation or electrokinetics alone, but this rate was realized throughout the whole process when the two technologies were alternated, with a degradation of 78.5% ± 2.0% for the n-hexadecane after 45 days of treatment.

Remedial effects of Potamogeton crispus L. on PAH-contaminated sediments

In this study, the remedial effects of submerged macrophyte Potamogeton crispus L. on polycyclic aromatic hydrocarbon (PAH)-contaminated sediments were investigated. After a 54-day experiment, the dissipation ratios of phenanthrene and pyrene were 84.8-88.3 and 72.4-78.5% in rhizosphere sediments, which were significantly higher than those in non-rhizosphere sediments (54.2-66.6 and 54.7-58.5%). The dissipation increment increased not only with increasing spiked concentration, but also over time, while plant uptake accounted for only a small portion (<6%) of the dissipation increment. Moreover, bioavailable fraction tests revealed that biodegradation was not controlled by the amount of bioavailable PAHs. For better understanding of the microbial mechanism involved, phospholipid fatty acid (PLFA) profiles were analyzed. Biomass of microorganisms indicated by the total PLFA content was higher in rhizosphere sediments than in non-rhizosphere sediments and was related well to the dissipation ratios of the two PAHs. Cluster analysis showed that community structure significantly changed in rhizosphere sediments. Moreover, the increments of PAH dissipation in rhizosphere sediments had a strong positive correlation with those of polyphenol oxidase activities in the same media. It can be concluded that the enhanced remediation of PAHs by P. crispus was mainly due to the increase of microbial biomass and activity as well as changes of microbial community structure in sediments as a result of plant growth stimulation.

Remediation of PAH-contaminated soil by the combination of tall fescue, arbuscular mycorrhizal fungus and epigeic earthworms

A 120-day experiment was performed to investigate the effect of a multi-component bioremediation system consisting of tall fescue (Festuca arundinacea), arbuscular mycorrhizal fungus (AMF) (Glomus caledoniun L.), and epigeic earthworms (Eisenia foetida) for cleaning up polycyclic aromatic hydrocarbons (PAHs)-contaminated soil. Inoculation with AMF and/or earthworms increased plant yield and PAH accumulation in plants. However, PAH uptake by tall fescue accounted for a negligible portion of soil PAH removal. Mycorrhizal tall fescue significantly enhanced PAH dissipation, PAH degrader density and polyphenol oxidase activity in soil. The highest PAH dissipation (93.4%) was observed in the combination treatment: i.e., AMF+earthworms+tall fescue, in which the soil PAH concentration decreased from an initial value of 620 to 41 mg kg(-1) in 120 days. This concentration is below the threshold level required for Chinese soil PAH quality (45 mg kg(-1) dry weight) for residential use.

Influence of Oil Contamination on Physical and Biological Properties of Forest Soil After Chainsaw Use

Forestry works using chainsaws result in up to 7 million liters of various mineral oils being soaked annually into forest soils. These substances, containing a complex mixture of polycyclic aromatic hydrocarbons (PAHs), are highly toxic. The aim of the study was to determine the effect of oil contamination with PAHs on the physical and biological properties of forest soils. The study area was located in southern Poland in the Miechów forest district. The experiment was conducted on four treatment blocks with various amounts of oil addition. The study included the determination of PAH content, dehydrogenase and urease activity, and biomass of earthworms. Physical properties were determined using the dryer method and Kopecky rings of 250 cm³ volume. The results obtained confirmed the hypothesis that oil contamination with PAHs modified the physical properties of forest soils and oil had a negative impact on enzyme activity in soil. Enzyme activity in the studied soils was negatively correlated with PAH content. Earthworm population density reflected the contamination level of oil-contaminated soils.

Soil Dehydrogenases as an Indicator of Contamination of the Environment with Petroleum Products

The aim of the research was to compare the effects of various petroleum products, biodiesel, diesel oil, fuel oil and unleaded petrol on soil dehydrogenases, and to evaluate biostimulation with compost and urea in the restoration of homeostasis of the soil contaminated with these products. The obtained results allowed for defining the weight of dehydrogenases in monitoring of the environment subjected to pressure from petroleum hydrocarbons. The studies were carried out under laboratory conditions for 180 days, and loamy sand was the soil formation used in the experiment. The petroleum products were used in the following amounts: 0, 2, 4, 8 and 16 g kg^-1 DM of soil. Indices of the influence of the petroleum product and the stimulating substance on the activity of dehydrogenases were calculated. It was proved that the petroleum products affect soil dehydrogenases in various ways. Biodiesel, diesel oil and fuel oil stimulate these enzymes, while petrol acts as an inhibitor. Among the substances tested regarding biostimulation of soils contaminated with petroleum products, compost is definitely more useful than urea, and therefore, the former should be used for the remediation of such soils. Stimulation of dehydrogenases by compost, both in contaminated and non-contaminated soils, proves that it may accelerate microbiological degradation of petroleum-derived contaminants.

Electrochemical and spectroscopic characteristics of dissolved organic matter in a forest soil profile

Dissolved organic matter (DOM) represents one of the most mobile and reactive organic compounds in ecosystem and plays an important role in the fate and transport of soil organic pollutants, nutrient cycling and more importantly global climate change. Electrochemical methods were first employed to evaluate DOM redox properties, and spectroscopic approaches were utilized to obtain information concerning its composition and structure. DOM was extracted from a forest soil profile with five horizons. Differential pulse voltammetry indicated that there were more redox-active moieties in the DOM from upper horizons than in that from lower horizons. Cyclic voltammetry further showed that these moieties were reversible in electron transfer. Chronoamperometry was employed to quantify the electron transfer capacity of DOM, including electron acceptor capacity and electron donor capacity, both of which decreased sharply with increasing depth. FT-IR, UV-Vis and fluorescence spectra results suggested that DOM from the upper horizons was enriched with aromatic and humic structures while that from the lower horizons was rich in aliphatic carbon, which supported the findings obtained by electrochemical approaches. Electrochemical approaches combined with spectroscopic methods were applied to evaluate the characteristics of DOM extracted along a forest soil profile. The electrochemical properties of DOM, which can be rapidly and simply obtained, provide insight into the migration and transformation of DOM along a soil profile and will aid in better understanding of the biogeochemical role of DOM in natural environments.

Enhanced root exudation stimulates soil nitrogen transformations in a subalpine coniferous forest under experimental warming

Despite the perceived importance of exudation to forest ecosystem function, few studies have attempted to examine the effects of elevated temperature and nutrition availability on the rates of root exudation and associated microbial processes. In this study, we performed an experiment in which in situ exudates were collected from Picea asperata seedlings that were transplanted in disturbed soils exposed to two levels of temperature (ambient temperature and infrared heater warming) and two nitrogen levels (unfertilized and 25 g N m(-2)  a(-1) ). Here, we show that the trees exposed to an elevated temperature increased their exudation rates I (μg C g(-1) root biomass h(-1) ), II (μg C cm(-1)  root length h(-1) ) and III (μg C cm(-2)  root area h(-1) ) in the unfertilized plots. The altered morphological and physiological traits of the roots exposed to experimental warming could be responsible for this variation in root exudation. Moreover, these increases in root-derived C were positively correlated with the microbial release of extracellular enzymes involved in the breakdown of organic N (R(2)  = 0.790; P = 0.038), which was coupled with stimulated microbial activity and accelerated N transformations in the unfertilized soils. In contrast, the trees exposed to both experimental warming and N fertilization did not show increased exudation rates or soil enzyme activity, indicating that the stimulatory effects of experimental warming on root exudation depend on soil fertility. Collectively, our results provide preliminary evidence that an increase in the release of root exudates into the soil may be an important physiological adjustment by which the sustained growth responses of plants to experimental warming may be maintained via enhanced soil microbial activity and soil N transformation. Accordingly, the underlying mechanisms by which plant root-microbe interactions influence soil organic matter decomposition and N cycling should be incorporated into climate-carbon cycle models to determine reliable estimates of long-term C storage in forests.

Degradation of polycyclic aromatic hydrocarbons by Pseudomonas sp. JM2 isolated from active sewage sludge of chemical plant

It is important to screen strains that can decompose polycyclic aromatic hydrocarbons (PAHs) completely and rapidly with good adaptability for bioremediation in a local area. A bacterial strain JM2, which uses phenanthrene as its sole carbon source, was isolated from the active sewage sludge from a chemical plant in Jilin, China and identified as Pseudomonas based on 16S rDNA gene sequence analysis. Although the optimal growth conditions were determined to be pH 6.0 and 37 degrees C, JM2 showed a broad pH and temperature profile. At pH 4.5 and 9.3, JM2 could degrade more than 40% of fluorene and phenanthrene (50 mg/L each) within 4 days. In addition, when the temperature was as low as 4 degrees C, JM2 could degrade up to 24% fluorene and 12% phenanthrene. This showed the potential for JM2 to be applied in bioremediation over winter or in cold regions. Moreover, a nutrient augmentation study showed that adding formate into media could promote PAH degradation, while the supplement of salicylate had an inhibitive effect. Furthermore, in a metabolic pathway study, salicylate, phthalic acid, and 9-fluorenone were detected during the degradation of fluorene or phenanthrene. In conclusion, Pseudomonas sp. JM2 is a high performance strain in the degradation of fluorene and phenanthrene under extreme pH and temperature conditions. It might be useful in the bioremediation of PAHs.

2-Phenyl-2,3-dihydrophenanthro[9,10-b][1,4]dioxine

In the title compound, C₂₂H₁₆O₂, the phenanthrene ring system is essentially planar [maximum deviation = 0.058 (1) Å] and is inclined at an angle of 58.39 (6)° to the phenyl ring. The 1,4-dioxane ring is in a chair conformation. In the crystal, mol­ecules are stacked along the b axis, but no significant hydrogen bonds are observed.