Enhanced bioremediation of PAH-contaminated soil by wheat bran and microbial community response

ABSTRACT

Microcosms were set up containing a PAH polluted soil to investigate biostimulation (addition of wheat bran and fertilizer) and bioaugmentation (inoculation with Pseudomonas sp. SB). After 60 d the fertilizer + wheat bran gave the highest PAH degradation. The degradation rate was 42.2%, significantly higher than the 18.7% in the fertilizer only treatment. Principal coordinate analysis (PCoA) indicates that wheat bran treatment can significantly alter soil bacterial and fungal communities. In addition, wheat bran promoted the enrichment of some soil bacteria such as Bacillaceae, Xanthomonadaceae, Streptomycetaceae, and Chitinophagaceae, and the fungi Talaromyces, Humicola, unclassified_Chaetomiaceae and Mortierella. These results highlight the potential of wheat bran application to reduce the PAHs detected in soil.     

Enhancement of maize plant growth with inoculation of phosphate-solubilizing bacteria and biochar amendment in soil

Maize plant has an absolute requirement of nutrients (N, P, and K) for growth and development. The microbial application can facilitate in addressing limited access to chemical fertilizer concern. Moreover, biochar and phosphorus-solubilizing bacterial (PSB) community can contribute together in nutrient availability. Both have the P-supply potential to the soil, but their interaction has been tested less under semiarid climatic conditions. The purpose of the study was to evaluate the potential of biochemically tested promising PSB strains and biochar for maize plant growth and nutritional status in plant and soil. Therefore, two isolated PSB strains from maize rhizosphere were biochemically tested in vitro and identified by 16S rDNA gene analysis. The experiment was conducted in the greenhouse where the plant growth and nutrient availability to the plants were observed. In this regard, all the treatments such as PSB strain-inoculated plants, biochar-treated plants, and a combination of PSBs + biochar-treated plants were destructively sampled on day 45 (D₄₅) and day 65 (D₆₅) of sowing with four replications at each time. PSB inoculation, biochar incorporation, and their combinations have positive effects on maize plant height and nutrient concentration on D₄₅ and D₆₅. In particular, plants treated with sawdust biochar + Lysinibacillus fusiformis strain 31MZR inoculation increased N (32.8%), P (72.5%), and K (42.1%) against control on D₆₅. Besides that, only L. fusiformis strain 31MZR inoculation enhanced N (23.1%) and P (61.5%) than control which shows the significant interaction of PSB and biochar in nutrient uptake. PSB and biochar have the potential to be used as a promising amendment in improving plant growth and nutrient absorption besides the conventional approaches.     

Enhanced sorption of polycyclic aromatic hydrocarbons by soil amended with biochar

Purpose  

Polycyclic aromatic hydrocarbon (PAHs) are ubiquitous pollutants in agricultural soils in China. Biochar is the charred product of biomass pyrolysis, which is widely applied to soils to sequestrate atmospheric carbon dioxide and guarantees a long-term benefit for soil fertility. Knowledge about the impacts of various biochars on soil sorption affinity remains obscure. In this study, we evaluated the effects of various biochars on PAHs sorption to biochar-amended agricultural soil.     

Alginate microbeads as inoculant carriers for plant growth-promoting bacteria

A method of inoculating wet and dry seeds with plant growth-promoting bacteria (PGPB) using alginate microbeads as a substrate and Azospirillum brasilense as the model PGPB was developed. The microbeads were produced by low pressure spraying of an alginate solution mixed with liquid bacterial culture suspended in a very rich medium through a small nozzle resulting in small-diameter droplets. These droplets, when sprayed into a slowly stirred solution of CaCl₂, immediately hardened into microbeads at diameters ranging between 100 and 200 µm. Although the process killed part of the entrapped bacteria, the remaining bacteria residing in the microbeads were sufficient [>10¹¹ colony-forming units (CFU) g^-1 inoculant] for seed inoculation. Further, it was found that the bacterial population in the inoculant could be enhanced by secondary multiplication in the same medium for an additional 16 h. It was found that the microbeads could be used either wet or dry. Dry inoculant was produced using dry air at 38°C, creating a powdery substance loaded with >10⁹ CFU g^-1 beads. Alternatively, dry microbeads were produced using a standard freeze-drying procedure. This dry preparation was easily attached to dry seed surfaces with the addition of 1% alcohol-diluted lecithin or with 0.5% synthetic paper adhesive (Resistol). The bacteria were slowly released from the microbeads in amounts ranging from 10⁴ to 10⁶ CFU g^-1 depending on the type (wet or dry, with or without skim milk) and the time of incubation (the longer the incubation period, the smaller the amount of bacteria released with time). The wet and dry inoculants enhanced the development of wheat and tomato seedlings growing in unfertile soil, and biodegraded within 15 days in moist soil.     

Mineralization of plant residues and native soil carbon as affected by soil fertility and residue type

Journal of Soils and Sediments - Crop residue return is an effective and low-cost agricultural approach for soil organic carbon (SOC) sequestration. Yet, it is largely unknown to what extent the...     

Enhanced non-extractable residue formation of 14C-metalaxyl catalyzed by an immobilized laccase

We studied the influence of an immobilized laccase from Trametes versicolor on non-extractable residue (NER) formation of the systemic fungicide ¹⁴C-metalaxyl in soil. We added the enzyme (130 mU/g DW) to soil sterilized by gamma irradiation and observed that the amount of NER (6.3 % of applied radioactivity) after 10 days of incubation was enhanced about twofold compared to the sterile soil without laccase addition. Residues formed within samples without enhanced enzyme activity were mainly bound via ester linkages to all fractions of humic matter, i.e., fulvic acids, humic acids, non-humines, and humines, respectively. In contrast, residues formed in presence of immobilized laccase were more strongly bound by covalent linkages such as ether and C-C bonds, especially to humic acids. After chemical degradation of the humic matter, it could be observed that all NER contained the first major transformation product, i.e., metalaxyl acid. The findings underline that the residue formation of metalaxyl in soil may be partly catalyzed by immobilized extracellular oxidative enzymes through oxidative coupling reactions within the humic matter.     

多环芳烃污染土壤的微生物与植物联合修复研究进展

本文综述了多环芳烃(PAHs)污染土壤中微生物降解途径、机理及生物反应器的应用,并从植物修复角度,进一步阐述了与微生物联合作用促进污染土壤中PAHs降解的途径、机理及其应用。提出了利用微生物共代谢降解及其与植物联合修复PAHs污染土壤环境的生物修复技术未来研究课题。     

A comparison of three atrazine-degrading bacteria for soil bioremediation

The ability of three atrazine-degrading bacteria, Pseudomonas sp. strain ADP, a Pseudaminobacter sp., and a Nocardioides sp., to degrade and mineralize this herbicide in a loam soil was evaluated in laboratory microcosms. These bacteria all hydrolytically dechlorinate atrazine, and degrade atrazine in pure culture with comparable specific activities. The Pseudaminobacter and Nocardioides can utilize atrazine as sole carbon and nitrogen source, whereas the Pseudomonas can utilize the compound only as a nitrogen source. The Pseudomonas and Pseudaminobacter mineralize the compound; the end product of atrazine metabolism by the Nocardioides is N-ethylammelide. At inoculum densities of 10⁵ cells/g soil, only the Pseudaminobacter and Nocardioides accelerated atrazine dissipation. The Pseudaminobacter mineralized atrazine rapidly and without a lag, whereas atrazine was mineralized in the Nocardioides-inoculated soil but only after a lag of several days. The Pseudaminobacter remained viable longer than did the Pseudomonas in soil. PCR analysis of recovered bacteria indicated that the genes atzA (atrazine chlorohydrolase) and atzB (hydroxyatrazine ethylaminohydrolase) were less stable in the Pseudaminobacter than the Pseudomonas. In summary, this study has revealed important differences in the ability of atrazine-hydrolyzing bacteria to degrade this compound in soil, and suggests that the ability to utilize atrazine as a carbon source is important to establish "enhanced degradation" by ecologically meaningful inoculum densities.     

Remediation of PAH-contaminated soil by pulsed corona discharge plasma

Purpose

Polycyclic aromatic hydrocarbons (PAHs) are hydrophobic organic pollutants of great environmental and health concern. PAHs are very persisted in soils and sediments which make it very difficult to remove them from soil. Therefore, remediation of PAH-contaminated sites has become an important environmental issue. The objective of this work was to study PAH degradation by pulsed corona discharge plasma system.

Materials and methods

Phenanthrene (Phe) was used as the model pollutant. The Phe-contaminated soil samples were prepared by adding appropriate amount of Phe dichlormethane solution (200 mg/L) into a given amount of pretreated soil, and Phe distributed uniformly in the soil at about 100 mg/kg. The experimental system mainly consisted of a pulse high-voltage power supply and a reactor vessel. The high-voltage electrode comprised of six stainless-steel needles and the ground electrode was a stainless-steel plate. The concentration of Phe was determined by HPLC system after being extracted out from soil. Effect of run parameters such as pulse voltage, pulse frequency, air flow rate, gas atmosphere, and initial concentration of Phe on Phe degradation was investigated, and the consumption of ozone during discharge process was also studied.

Results and discussion

The results showed that degradation efficiency of Phe (initial concentration 100 mg/kg) approached approximately 70 % after 40 min of discharge treatment under the conditions of pulse voltage 18 kV, pulse frequency 70 Hz, and air flow rate 0.8 L/min, which increased with the pulse voltage and pulse frequency due to the enhancement of input energy. An optimal air flow rate of 0.8 L/min was observed to obtain a maximum Phe degradation efficiency. Oxygen atmosphere favored Phe degradation due to high concentration of generated O-reagents, and ozone was found to act on Phe degradation. The concentration of Phe had influence on remediation capacity that increased with the amount of Phe in soil.

Conclusions

The results confirmed that pulsed corona-discharge plasma was a potential method for remediation of PAH-contaminated soil. This study offered a viable treatment option for remediation of Phe-contaminated soil, which was expected to remove PAHs other than Phe from soil with further development.

     

Enhanced bioremediation of soil containing 2,4-dinitrotoluene by a genetically modified Sinorhizobium meliloti

The symbiotic nitrogen-fixing soil bacterium, Sinorhizobium meliloti, is well known for its ability to interact with the leguminous plant Medicago sativa L. It has, however, not been reported that this species possesses the capability to degrade toxic nitroaromatic compounds, such as 2,4-dinitrotoluene (DNT) which is commonly associated with the degradation of the explosive trinitrotoluene (TNT). In this study, the pJS1 DNT-biodegradative plasmid was genetically transferred to S. meliloti strain USDA 1936, which was confirmed by plasmid profile analysis. Several standard analytical and chemical tests including high performance liquid chromatography (HPLC), nitrite (NO₂) release assays, rhizosphere population and plant greenhouse studies were conducted to test the ability of S. meliloti to degrade 2,4-DNT. The possible presence of 2,4-DNT remaining in the treated soil was tested, and no 2,4-DNT had been absorbed by the soil. The pJS1-carrying recombinant strain DHK1 produced ‘ARC’ alfalfa plants that were almost 2-fold higher in shoot dry weight than that produced by the parent strain on soil containing 0.14 mM 2,4-DNT. The transconjugant strain DHK1 reduced significantly one-third more 2,4-DNT in both 0.14 and 0.28 mM contaminated soil, and in 0.55 mM contaminated soil it degraded 94% of the 2,4-DNT present. In liquid cultures, however, only about 4% reduction in 2,4-DNT concentrations was obtained in 10 days. We interpret the results as clearly establishing that genetic modification was successfully used, for the first time, to improve the capability of the symbiotic nitrogen-fixing soil bacterium S. meliloti DHK1 to bioremediate in situ 2,4-DNT-contaminated soil in the presence of alfalfa plants.     

Interrill soil erosion as affected by tillage and residue cover

No-till cropping systems are effective in reducing soil erosion. The objective of this study was to determine whether high infiltration rates and low runoff and soil loss under long-term, no-till conditions in loessial regions of the Midwest US result from both the well-structured, porous condition of the soil and the protective cover of crop residue or primarily from residue cover. Soil loss, runoff, and infiltration were measured using a rainfall simulator on interrill erosion plots with and without residue cover on a conventional and two no-till systems in central Illinois. For both conventional till and no-till conditions, removing surface residue significantly decreased infiltration rates and increased soil loss. Tilling the no-till surface while maintaining an equal surface cover as with the no-till system slightly increased interrill erosion. Removing residue on a no-till system, however, increased soil loss significantly. A no-till soil condition without adequate residue cover will seal, crust, and erode with extremely high soil losses following surface drying.     

Manure application followed by biochar application increases plant production regardless of soil dehydrogenase activity

Biochar is obtained by the pyrolysis of biomass, and contains abundant carbon and minerals. Biochar supplementation of soils can greatly improve soil health and quality, but these beneficial effects typically develop slowly over time. Depending on the quality of the biochar and the soil to which it is applied, it may take years before positive effects are apparent. This is because organic substances are slowly sorbed onto the biochar over time, and the biochar eventually becomes part of the sorption complex of the soil. It is therefore advisable to apply biochar together with some organic material. We examined the effect of co-application of different doses of biochar with manure on soil dehydrogenase activity (DHA), soil oxidizable carbon (COX), cumulative soil respiration, soil buffering capacity, the soil exchange reaction (pH/KCl) and the production yield of winter rape seeds. We also determined seed production when artificial granular fertilizers were added to biochar and manure. The results showed that the application of biochar and manure significantly increased grain yield, DHA, the soil exchange reaction and cumulative respiration. Thus, application of biochar with organic material can increase seed yield and some properties of agricultural soils. However, the positive effect of biochar on seed yield was not directly proportional to biochar dose, in that the seed yield was lower for a biochar dose of 45 t/ha than 30 t/ha.     

Low-cost and environmental-friendly Triticum aestivum-derived biochar for improving plant growth and soil fertility

ABSTRACT

Biochar and biochar–fertilizer concoction is imperative to subjugate reduced plant growth and soil fertility depletion which is a constraint for sustainable agriculture. The aspiration of the current research was to determine the plant growth response to wheat straw-derived biochar annexation in soils from two regions: Rawalpindi (semi-arid) and Thar (arid). Wheat straw (Triticum aestivum) was pyrolyzed at 300°C in a low-cost biochar retort kiln at different concentration rates (0%, 1%, 3%, and 7% by mass). Growth trend of Sorghum bicolor was observed in these soils for 40 days in a greenhouse. Fertilizer (NPK) (8.58% N, 4.39% P, and 3.48% K) was added to soil on the third day of seed germination. Soil physicochemical analysis, plant growth, and dry matter yield evaluation after the treatment signified the concomitant increase in dry matter yield along with enhanced soil fertility and plant growth.     

傅立叶变换红外光谱法表征玉米秆茬培肥土壤胡敏酸的变化

土壤腐殖质是土壤肥力的重要物质基础,在土壤有机碳库中占有相当大的比重,腐殖质可分成三个组分:胡敏酸(HA,不溶于酸),富里酸(FA,溶于酸)[1]和胡敏素(HM)。其中胡敏酸是土壤腐殖质中的活跃成分,其存在形态、分子组成、理化性质的变化对土壤的肥力特征都会产生巨大影响[2-3]。玉米植株残体作为有机肥的一个重要组成部分,施入土壤后必然对土壤HA的数量、组成、结构及存在形式产生影响,并使其理化性质发生改变,从而起到改善土壤环境和培肥土壤的作用。研究证明,玉米植株残体施入土壤后,土壤胡敏酸的理化性质得到显著的改善[4-5]。张晋京等…     

Temporal variations of crop residue effects on soil N transformation depend on soil properties as well as residue qualities

Purple soils (Eutric Regosols) are widely distributed in humid subtropical Southwest China. They are characterized by high nitrification activities, with risks of severe NO₃^? leaching. Incorporation of crop residues is considered an effective method to reduce NO₃^? loss. In the present study, we compared the effects of alfalfa, rice straw, and sugarcane bagasse on gross N transformation turnover in a purple soil (purple soil, pH 7.62) compared with those in an acid soil (acid soil, pH 5.26), at 12 h, 3 months, and 6 months after residue incorporation. The gross N transformation rates were determined by ¹⁵N tracing. All tested crop residues stimulated the gross N mineralization rates, but reduced the net mineralization rates in both soils at 12 h after residue incorporation; however, the extent of the effect varied with the crop residue qualities, with rice straw having the strongest effects. Crop residues reduced net nitrification rates by depressing gross autotrophic nitrification rates and stimulating NO₃^? immobilization rates in the purple soil, particularly after rice straw incorporation (net nitrification rate decreased from 16.72 mg N kg^?1 d^?1 in the control to ??29.42 mg N kg^?1 d^?1 at 12 h of residue incorporation); however, crop residues did not affect the gross autotrophic nitrification rates in the acid soil. Crop residue effects subsided almost completely within 6 months, with sugarcane bagasse showing the longest lasting effects. The results indicated that crop residues affected the N transformation rates in a temporal manner, dependent on soil properties and residue qualities.     

Maize productivity and soil carbon storage as influenced by wheat residue management

Wheat (Triticum aestivum L) residue removed, burnt, or incorporated with or without 0, 60, and 120 kg nitrogen (N) ha^?1 effects on maize (Zea mays L) hybrids (Pioneer-3025, Pioneer-30P45, and Kiramat) were assessed at University of Agriculture, Peshawar, Pakistan during 2010 and 2011 for maize production and soil carbon (C) storage. Pioneer-30P45 had higher grain yield, leaf area, and delayed maturity. Residue burning combined with 120 kg N ha^?1 produced higher grain yield. The leaf area, leaf area ratio, grain N content, and solar radiation interception were improved with N + residue burnt/incorporated over control. The grain yield was positively correlated with yield parameters. Soil organic carbon (SOC) content were in order of incorporated > burnt > removed at all growth stages (i.e., sowing, tasseling, maturity, and harvesting). Conclusively, wheat residue burnt/incorporated into the soil with 120 kg N ha^?1 was best for maize production of Pioneer-30P45; however residue incorporation into the soil improved SOC.     

Analysis of the dynamics of plant residue mineralization and humification in soil

The quantitative aspects of mineralization and humification of organic residues in soil were analyzed on the basis of the experimental curves of their transformation and using three conceptual approaches. Ågren’s and Bosatta’s concept of the continuum of substrate quality loss accentuates the gradual reduction of the availability of the decomposable material for microorganisms. The discrete succession concept emphasizes the existence of morphologically and biochemically distinguishable stages (a fraction cascade) of transforming the organic debris into humus. According to the biochemical concept, the organic debris transformation is represented as the mineralization of individual organic substances with different rates, more often without taking into account the influence of humus formation. The testing of these concepts led to the conclusion that the discrete succession and biochemical concepts should be integrated for the elaboration of the theoretical basis for assessing the rate of organic debris transformation in the soil.     

Effect of crop residue biochar on soil acidity amelioration in strongly acidic tea garden soils

Strongly acidic soil (e.g. pH < 5.0) is detrimental to tea productivity and quality. Wheat, rice and peanut biochar produced at low temperature (max 300 °C) and differing in alkalinity content were incorporated into Xuan‐cheng (Ultisol; initial pH_{soil/water = 1/2.5} 4.12) and Ying‐tan soil (Ultisol; initial pH _{soil/water = 1/2.5} 4.75) at 10 and 20 g/kg (w/w) to quantify their liming effect and evaluate their effectiveness for acidity amelioration of tea garden soils. After a 65‐day incubation at 25 °C, biochar application significantly (P < 0.05) increased soil pH and exchangeable cations and reduced Al saturation of both tea soils. Association of H⁺ ions with biochar and decarboxylation processes was likely to be the main factor neutralizing soil acidity. Further, biochar application reduced acidity production from the N cycle. Significant (P < 0.05) increases in exchangeable cations and reductions in exchangeable acidity and Al saturation were observed as the rate of biochar increased, but there were no further effects on soil pH. The lack of change in soil pH at the higher biochar rate may be due to the displacement of exchangeable acidity and the high buffering capacity of biochar, thereby retarding a further liming effect. Hence, a significant linear correlation between reduced exchangeable acidity and alkalinity balance was found in biochar‐amended soils (P < 0.05). Low‐temperature biochar of crop residues is suggested as a potential amendment to ameliorate acidic tea garden soils.