Fertilization and Bioaugmentation for Oil Biodegradation in Salt Marsh Mesocosms

Biodegradation of crude oil is often dependent on the population sizes and metabolic activity of hydrocarbon-degrading microorganisms in addition to nutrient supply. Fertilization with N and P and bioaugmentation of oil-contaminated soil with hydrocarbon-degrading microorganisms may serve to enhance oil biodegradation rates. Glasshouse experiments were conducted to determine the impacts of fertilization and commercial bioremediation products on crude oil biodegradation and on changes in nutrient concentrations and populations of hydrocarbon-degrading microorganisms in salt marsh mesocosms growing Spartina alterniflora. Experiments were conducted under continuously-flooded and alternately-flooded/drained conditions with and without N and P fertilization. MaxBac, a slow-release fertilizer, was applied at a rate of 100 kg N ha^-1 and 20 kg P ha^-1, while additional P was applied at 20 kg P ha^-1. Commercial products failed to enhance total oil or total petroleum hydrocarbon (TPH) degradation under either continuously or alternately-flooded conditions. An average of 62% of TPH was degraded by 33 d under continuously-flooded conditions, while 59% was degraded by 41 d after oil application under alternately-flooded conditions. Products generally did not increase population sizes of heterotrophs orhydrocarbon-degrading microorganisms. Concentrations of NH₄ ⁺ and P decreased during experimentation, and fertilization with N and P stimulated total oil and TPH degradation under continuously-flooded, but not under alternately-flooded conditions.     

Community structure of arbuscular mycorrhizal fungi associated with Robinia pseudoacacia in uncontaminated and heavy metal contaminated soils

The significance of arbuscular mycorrhizal fungi (AMF) in soil remediation has been widely recognized because of their ability to promote plant growth and increase phytoremediation efficiency in heavy metal (HM) polluted soils by improving plant nutrient absorption and by influencing the fate of the metals in the plant and soil. However, the symbiotic functions of AMF in remediation of polluted soils depend on plant–fungus–soil combinations and are greatly influenced by environmental conditions. To better understand the adaptation of plants and the related mycorrhizae to extreme environmental conditions, AMF colonization, spore density and community structure were analyzed in roots or rhizosphere soils of Robinia pseudoacacia. Mycorrhization was compared between uncontaminated soil and heavy metal contaminated soil from a lead–zinc mining region of northwest China. Samples were analyzed by restriction fragment length polymorphism (RFLP) screening with AMF-specific primers (NS31 and AM1), and sequencing of rRNA small subunit (SSU). The phylogenetic analysis revealed 28 AMF group types, including six AMF families: Glomeraceae, Claroideoglomeraceae, Diversisporaceae, Acaulosporaceae, Pacisporaceae, and Gigasporaceae. Of all AMF group types, six (21%) were detected based on spore samples alone, four (14%) based on root samples alone, and five (18%) based on samples from root, soil and spore. Glo9 (Rhizophagus intraradices), Glo17 (Funneliformis mosseae) and Acau3 (Acaulospora sp.) were the three most abundant AMF group types in the current study. Soil Pb and Zn concentrations, pH, organic matter content, and phosphorus levels all showed significant correlations with the AMF species compositions in root and soil samples. Overall, the uncontaminated sites had higher species diversity than sites with heavy metal contamination. The study highlights the effects of different soil chemical parameters on AMF colonization, spore density and community structure in contaminated and uncontaminated sites. The tolerant AMF species isolated and identified from this study have potential for application in phytoremediation of heavy metal contaminated areas.     

Recycling of Remediated Soil for Effective Composting Of Diesel-Contaminated Soil

Soil contaminated with diesel oil was remediated by the addition of remediated soil. Several mix ratios of contaminated soil to remediated soil were tested. Judging from TPH degradation rate and biochemical parameters, the optimum mix ratio (wet weight basis) was 1:1. In this mix ratio, the first order degradation rate constant of diesel oil based on TPH was 0.099/day. Degradation rate of TPH and total amount of CO₂ evolved in this condition were two times larger than those of contaminated soil without adding remediated soil. The addition of remediated soil was a very effective treatment option to facilitate the degradation rate of diesel oil in contaminated soil.     

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.     

Soil moisture levels affect mycorrhization during early stages of development of agroforestry plants

Plants respond differentially to different arbuscular mycorrhizal fungi (AMF) as well as to the different soil moisture levels. Based on this background, the present study was carried out to investigate the effects of different levels of soil moisture and AMF inoculations on mycorrhization and growth of important agroforestry plants, viz., Phaseolus mungo, Triticum aestivum, Eucalyptus tereticornis, and Albizia procera. The experiments consisted of main treatment, i.e., three levels of soil moisture [field capacity (FC?=?16 %), half-field capacity (FC/2?=?8 %) and double-field capacity (2×FC?=?32 %)] and four subtreatments (mycorrhizal inoculations), viz., Acaulospora scrobiculata, Glomus cerebriforme, Glomus intraradices, and un-inoculated (control). AMF inoculations significantly (P?<?0.05) increased growth and P uptake, in all tested plant species. In P. mungo, maximum AMF efficiency was observed at FC while in other plants, AMF were equally effective at FC/2 and 2×FC. Different inoculants were effective at different moisture levels. Furthermore, mycorrhization was the highest at FC. AMF inoculations were more important than soil moisture (explaining 33–97 % variation in growth) in P. mungo, T. aestivum, and A. procera (forward selection method), whereas soil moisture was more important for growth of E. tereticornis. Thus, it may be stated that depending upon soil moisture, inoculation of plants with suitable AMF consortium can be beneficial.     

Differential effects of soil disturbance and plant residue retention on function of arbuscular mycorrhizal (AM) symbiosis are not reflected in colonization of roots or hyphal development in soil

The effects of soil disturbance and residue retention on the functionality of the symbiosis between medic (Medicago truncatula L.) and arbuscular mycorrhizal fungi (AMF) were assessed in a two-stage experiment simulating a crop rotation of wheat (Triticum aestivum L.) followed by medic. Plants were inoculated or not with the AMF, Glomus intraradices and Gigaspora margarita, separately or together. The contribution of the arbuscular mycorrhizal (AM) pathway for P uptake was determined using ³²P-labeled soil in a small hyphal compartment accessible only to hyphae of AMF. In general AM colonization was not affected by soil disturbance or residue application and disturbance did not affect hyphal length densities (HLDs) in soil. At 4 weeks disturbance had a negative effect on growth and phosphorus (P) uptake of plants inoculated with G. margarita, but not G. intraradices. By 7 weeks disturbance reduced growth of plants inoculated with G. margarita or AMF mix and total P uptake in all inoculated plants. With the exception of plants inoculated with G. margarita in disturbed soil at 4 weeks, the AM pathway made a significant contribution to P uptake in all AM plants at both harvests. Inoculation with both AMF together eliminated the negative effects of disturbance on AM P uptake and growth, showing that a fungus insensitive to disturbance can compensate for loss of contribution of a sensitive one. Application of residue increased growth and total P uptake of plants but decreased ³²P in plants inoculated with the AMF mix in disturbed soil, compared with plants receiving no residue. The AMF responded differently to disturbance and G. intraradices, which was insensitive to disturbance, compensated for lack of contribution by the sensitive G. margarita when they were inoculated together. Colonization of roots and HLDs in soil were not good predictors of the outcomes of AM symbioses on plant growth, P uptake or P delivery via the AM pathway.     

丛枝菌根真菌促进植物摄取土壤磷的作用机制

磷在土壤中易被固定沉淀,在植物磷利用率低的情况下,过度施肥会造成磷肥浪费,可能通过地表径流、地下水溶解等方式,造成水体富营养化产生面源污染,对人类生产生活造成较大影响。丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)和植物结合所形成的共生菌根可以显著增强植株对磷的吸收利用。通过AMF可以提高宿主植株对磷的吸收转运的特性,从AMF促进植株对磷元素的摄取机制、AMF促进植物磷摄取分子机理、AMF作用下根系分泌物对植株磷利用的影响与根际微生物对AMF磷元素利用的影响4个方面的研究进展进行分析总结。AMF可以通过改变宿主植株的根系形态和菌丝网络的形成,扩大植株对养分吸收范围;释放有机酸、磷酸酶和质子等根系分泌物改变土壤结构和理化性质,与根际微生物共同作用降解土壤中难溶性磷酸盐;诱导相关磷转运蛋白基因的特异性表达,提高植株对磷的转运能力而促进其吸收。     

Distribution of arbuscular mycorrhizal fungi spores in soils of smallholder agroforestry and monocultural coffee systems in southwestern Ethiopia

Arbuscular mycorrhizal fungi (AMF) are associated with the root system of coffee (Coffea arabica L.) plants, but their distribution in smallholder agroforestry and monocultural coffee systems is not well known. This study investigates the spatial distribution of AMF spores in a field study in southwestern Ethiopia. Soil samples from different depths (0–50 cm) were collected under the tree canopies of Acacia abyssinica, Albizia gummifera, Ficus sur, Ficus vasta and randomly selected unshaded coffee plants at different sampling points (canopy base, radius, edge and outside canopy). Significantly higher AMF spore densities were recorded at canopy bases and at 0–30 cm soil depth. Spore populations were found to belong to five genera: Acaulospora, Entrophospora, Glomus, Gigaspora and Scutellospora, with Glomus and Acaulospora dominating. Sampling points, sites and depths, shade tree species and shade tree/coffee plant age affected AMF spore density. Agroforestry practices including the use of leguminous shade trees effectively maintained AMF numbers in soils even at depth compared with unshaded coffee plants (monocultures).     

Molecular diversity of arbuscular mycorrhizal fungi associated with an Mn hyperaccumulator—Phytolacca americana,in Mn mining area

Arbuscular mycorrhizal fungi (AMF) have great potential for assisting metal-hyperaccumulating plants in the remediation of contaminated soils. However, little information is available about the symbiosis and community composition of AMF associated with manganese (Mn) hyperaccumulator, such as Phytolacca americana, growing on Mn-contaminated soils under natural conditions. Therefore, the objective of this study was to analyze AMF diversity and community composition in P. americana roots growing at an Mn mining site. Molecular techniques were used to analyze AMF community composition and phylogenetic relationship in P. americana roots sampled from three Mn mine spoils and one adjacent reference areas. Results obtained showed that mycorrhizal symbionts successfully established even in the most heavily Mn-polluted sites. Root colonization and AMF diversity were significantly negatively correlated with total and extractable Mn concentrations. Principal component analysis (PCA) revealed that Mn contamination impacted AMF diversity, and shaped AMF community structure. Phylogenetic analyses demonstrated that all species were affiliated with Glomus, suggesting that Glomus was the dominant genus in this AMF community. Some unique sequences that occurred exclusively in heavily polluted sites associated with P. americana may belong to symbiotic fungi with great potential for improving the phytoremediation efficiency of Mn-contaminated soils.     

Differential effect of arbuscular mycorrhizal fungal communities from ecosystems along management gradient on the growth of forest understorey plant species

Arbuscular mycorrhizal fungi (AMF) are important functional components of ecosystems. Although there is accumulating knowledge about AMF diversity in different ecosystems, the effect of forest management on diversity and functional characteristics of AMF communities has not been addressed. Here, we used soil inoculum representing three different AM fungal communities (from a young forest stand, an old forest stand and an arable field) in a greenhouse experiment to investigate their effect on the growth of three plant species with contrasting local distributions - Geum rivale, Trifolium pratense and Hypericum maculatum. AM fungal communities in plant roots were analysed using the terminal restriction fragment length polymorphism (T-RFLP) method. The effect of natural AMF communities from the old and young forest on the growth of studied plant species was similar. However, the AMF community from the contrasting arable ecosystems increased H. maculatum root and shoot biomass compared with forest inocula and T. pratense root biomass compared to sterile control. According to ordination analysis AMF inocula from old and young forest resulted in similar root AMF communities whilst plants grown with AM fungi from arable field hosted a different AMF community from those grown with old forest inocula. AMF richness in plant roots was not related to the origin of AMF inoculum. G. rivale hosted a significantly different AM fungal community to that of T. pratense and H. maculatum. We conclude that although the composition of AM fungal communities in intensively managed stands differed from that of old stands, the ecosystem can still offer the ‘symbiotic service’ necessary for the restoration of a characteristic old growth understorey plant community.     

Do the impacts of alien invasive plants differ from expansive native ones? An experimental study on arbuscular mycorrhizal fungi communities

No studies have compared so far the effects of alien invasive and expansive native (widespread, mono-dominant) plants on arbuscular mycorrhizal fungi (AMF). Four global or European most successful invaders (Impatiens glandulifera, Reynoutria japonica, Rudbeckia laciniata, Solidago gigantea) and two expansive plants native to Europe (Artemisia vulgaris, Phalaris arundinacea) were grown in pots to elucidate the magnitude and direction of changes in AMF abundance, species richness, and species composition in soils from under multispecies native vegetation. In a second stage, the effects of these changes on a native plant, Plantago lanceolata, were assessed. Plant species identity had larger impact on AMF abundance, species richness, and species composition as well as on P. lanceolata than origin of the species (alien vs. native). This could be due to the character of AMF relationships with the plants, i.e., their mycorrhizal status and dependency on AMF. However, the alterations induced by the plant species in soil chemical properties rather than in AMF community were the major drivers of differences in shoot mass and photosynthetic performance of P. lanceolata. We determined that the plants produced species-specific effects on soil properties that, in turn, resulted in species-specific soil feedbacks on the native plant. These effects were not consistent within groups of invaders or natives.     

Controlled ectomycorrhization of an exotic legume tree species Acacia holosericea affects the structure of root nodule bacteria community and their symbiotic effectiveness on Faidherbia albida, a native Sahelian Acacia

Many fast growing tree species have been introduced to promote biodiversity rehabilitation on degraded tropical lands. Although it has been shown that plant productivity and stability are dependent on the composition and functionalities of soil microbial communities, more particularly on the abundance and diversity of soil symbiotic micro-organisms (mycorrhizal fungi and rhizobia), the impact of tree introduction on soil microbiota has been scarcely studied. This research has been carried in a field plantation of Acacia holosericea (Australian Acacia species) inoculated or not with an ectomycorrhizal fungus isolate, Pisolithus albus IR100. After 7 year's plantation, the diversity and the symbiotic properties of Bradyrhizobia isolated from the plantation soil or from the surrounding area (Faidherbia albida (Del.) a. Chev. parkland) and able to nodulate F. albida, a native Sahelian Acacia species, have been studied. Results clearly showed that A. holosericea modified the structure of Bradyrhizobia populations and their effectiveness on F. albida growth. This negative effect was counterbalanced by the introduction of an ectomycorrhizal fungus, P. albus, on A. holosericea root systems.In conclusion, this study shows that exotic plant species can drastically affect genotypic and symbiotic effectiveness of native Bradyrhizobia populations that could limit the natural regeneration of endemic plant species such as F. albida. This effect could be counterbalanced by controlled ectomycorrhization with P. albus. These results have to be considered when exotic tree species are used in afforestation programs that target preservation of native plants and soil ecosystem rehabilitation.     

The HFC/HCFC breakdown product trifluoroacetic acid (TFA) and its effects on the symbiosis between Bradyrhizobium japonicum and soybean (Glycine max)

The environmental impact of hydrofluorocarbon (HFC) and hydrochlorofluorocarbon (HCFC) are under intense study due to the resistance of the breakdown product, trifluoroacetic acid (TFA), to further degradation. TFA has come under scrutiny due to its rapid and complete partitioning into aqueous phases of the environment, eventually allowing for deposition of TFA into soil via precipitation. Evidence exists that TFA may be toxic to soil microbes and plants, with little or no degradation occurring in soils. Uptake by plants and microorganisms and its similarity to acetate, implies its potential to effect the symbiotic nitrogen-fixing partners Bradyrhizobium japonicum and soybean (Glycine max). A preliminary study was performed in accordance with the Alternative Fluorocarbon Environmental Acceptability Study (AFEAS). Those results are presented here in addition to the findings of further experimentation on the initial interaction of B. japonicum with soybean. We used three levels of TFA (0.67, 6.74 and 67.40 μl TFA kg⁻¹ soil; 0.003, 0.031 and 0.314 μl TFA l⁻¹) for soil and hydroponics conditions and three levels (10, 100 μM and 1 mM) in bacterial culture. The results demonstrate that TFA affects growth of B. japonicum significantly, but does not affect PHB accumulation. Also no F⁻ was found in cultures grown on TFA. Attachment of B. japonicum to soybean roots was enhanced with the lowest level of acetate or TFA and was significantly reduced with 1 mM acetate or TFA. Cultures grown on acetate or acetate with TFA do not attach well, with those grown with 1 mM TFA the least. Both effects may be attributed to pH. Soybean seedlings had significantly retarded development with levels of TFA at or above 6.74 μl TFA kg⁻¹ soil and 0.031 μl TFA l⁻¹ nutrient solution. No nodules formed on those plants treated with these levels of TFA except in the hydroponics trials. Nodule location was not affected regardless of the TFA level. At the lowest level used we found no effects on soybean or symbiotic nitrogen fixation. In some cases, nodulation was enhanced, but nodule weight reduced. Anaerobically isolated bacteroids had normal levels of acetylene reduction activity regardless of the level of TFA used. In summary, soybean is much more sensitive to low levels of TFA than its symbiotic counterpart B. japonicum. No detrimental effects on symbiotic nitrogen fixation in soybean should be expected unless large bioaccumulation of TFA occurs in agricultural areas.     

Effect of rhizobia,mycorrhizal fungi and phosphate-solubilizing microorganisms in the rhizosphere of native plants used to recover an iron ore area in Brazil

The iron-ore deposits in Minas Gerais state are concentrated in an area named Ferruginosous Quadrilateral, in which the dominant vegetation belongs to the Cerrado biome (savanna type, called campo rupestre or rupestrian field). This vegetation occurs in altitudes higher than 1000 m and is one of the most endangered biomes of the world. This study aimed to restore an area of rupestrian field used to keep iron-ore products, in which vegetation had been cut and thus resilience did not occur, worsening the low fertility of the fragile soil. Therefore, a revegetation model was proposed using two native species, Centrosema coriaceum (Leguminosae) and Tibouchina multiflora (Melastomataceae), inoculated with selected strains of arbuscular mycorrhizal fungi (AMF) and/or a rhizobium strain. After 48 months of plantation, the plant growth, survival index, physical and chemical soil properties, leaf nitrogen (N) and phosphorous (P), and P soil were evaluated. Inoculated plants benefited in all the analyzed aspects. While T. multiflora presented increased P content in leaves and soil rhizosphere only in inoculated plants, C. coriaceum showed the highest P content in both leaves and soil independently of inoculation. Although the inoculated plants presented more intense root colonization (AMF), the same mycorrhizal species were found in both inoculated and non-inoculated plants of C. coriaceum and T. multiflora. However, species of the Gigasporaceae family were favored in the C. coriaceum rhizosphere, as compared with T. multiflora. In addition, C. coriaceum was able to select in its rhizosphere a rhizobia strain efficient in P solubilization and a large and efficient population of phosphorus solubilizing microorganisms (PSM), preferentially composed of fungi. Through the similarity of their Internal Transcribed Spacer (ITS) sequences, the PSM fungi were identified as Fusarium oxysporum and Aspergillus fischeri using the BLAST database. The data presented suggest that C. coriaceum showed a strong rhizosphere effect in favor of a tripartite action of rhizobia, fungi and AMF populations as strategies to solubilize soil phosphate for survival and plant growth in the rupestrian field. Therefore, the inoculation of these microorganisms is desirable for mine recover.     

不同土壤类型下AM 真菌分布多样性及与土壤因子的关系

以禾本科植物群落为研究对象, 研究了宁夏六盘山林地、银川农耕地、暖泉农耕地、固原农耕地、盐池沙地、灵武沙地6 个采样地点5 种土壤类型(黑垆土、灌淤土、黄绵土、灰钙土、风沙土)下AM 真菌物种多样性及其与土壤因子的关系。结果表明: 5 种土壤类型采样点的植被根际土壤中共鉴定出5 属48 种AM真菌, 其中, 无梗囊霉属(Acaulospora)1 种, 巨孢囊霉属(Gigaspora)3 种, 球囊霉属(Glomus)37 种, 类球囊霉属(Paraglomus)1 种, 盾巨孢囊霉属(Scutellospora)6 种, 各采样点土壤均以球囊霉属为优势属。地球囊霉(G.geosporum)和木薯球囊霉(G. manihotis)是6 个采样地点中的优势种。不同土壤类型各采样点AM 真菌各属的频度存在明显差异, 球囊霉属在各点均有出现, 频度值最高。具有较高植被多样性的暖泉样点, AM 真菌的种属数量较多。土壤环境因子对AM 真菌孢子密度的影响因所处土壤、植被类型不同而异。pH、全盐、速效钾、速效磷等土壤肥力因子, 在PCA 轴上能最大程度地解释AM 真菌孢子密度与土壤环境因子之间相互关系的大部分信息。宁夏不同土壤类型区域中AM 真菌种类及分布一定程度上与该采样点的植被类型、植物多样性和土壤肥力特征相对应。     

Effects of interactions between arbuscular mycorrhizal fungi and bacteria on the growth of Lotus corniculatus L.: From the perspective of regulating rhizosphere fungal community

Arbuscular mycorrhizal fungi (AMF) provide essential nutrients to crops and are affected by fertilizers. Phosphate-solubilizing bacteria (PSB), nitrogen-fixing bacteria (NFB), and AMF have mutually beneficial relationships with plants, but the effects of their interactions on plant growth by regulating rhizosphere fungal community have not been sufficiently studied. In this study, a greenhouse pot experiment was conducted to investigate the interactions between AMF and bacteria (PSB and NFB) on the growth of Lotus corniculatus L. Specifically, the role of rhizosphere fungal community in the growth of Lotus corniculatus L. was explored using Illumina MiSeq high-throughput sequencing. The results showed that combined inoculation of AMF with PSB and NFB increased plant biomass, plant height, and fungal colonization rate. The richness, complexity, and stability of rhizosphere fungal community also increased after combined inoculation of AMF with PSB and/or NFB, particularly with PSB. In addition, combined inoculation of AMF with PSB and NFB enriched the abundance of beneficial microorganisms, with Chaetomium and Humicola showing the greatest alterations. The structural equation model showed that the interactions of AMF with PSB and NFB promoted plant growth by affecting fungal network structure and soil enzyme activities involved in carbon, nitrogen, and phosphorus cycling. These findings provide evidence for the effects of interactions of AMF with PSB and NFB on rhizosphere fungal community and plant growth.     

Effects of biochar on copper immobilization and soil microbial communities in a metal-contaminated soil

Purpose

Copper (Cu) contamination has been increasing in land ecosystems. Biochars (BCs) and arbuscular mycorrhizal fungi (AMF) are known to bind metals, and metallophyte can remove metals from soils. Will BC in combination with AMF contain the Cu uptake by a metallophyte growing in a metal-contaminated soil? The objective of this study was to investigate the effects of BCs on the Cu immobilization and over soil microbial communities in a metal-contaminated soil in the presence of AMF and metallophyte.

Materials and methods

Two BCs were produced from chicken manure (CMB) and oat hull (OHB). A Cu-contaminated sandy soil (338 mg kg^?1) was incubated with CMB and OHB (0, 1, and 5 % w/w) for 2 weeks. Metallophyte Oenothera picensis was grown in pots (500 mL) containing the incubated soils in a controlled greenhouse for 6 months. A number of analyses were conducted after the harvest. These include plant biomass weight, microbial basal respiration, and dehydrogenase activity (DHA), AMF root colonization, spore number, and glomalin production; changes in fungal and bacterial communities, Cu fractions in soil phases, and Cu uptake in plant tissues.

Results and discussion

The BCs increased the soil pH, decreased easily exchangeable fraction of Cu, and increased organic matter and residual fraction of Cu. The BCs provided favorable habitat for microorganisms, thereby increasing basal respiration. The CMB increased DHA by ～62 and ～574 %, respectively, for the low and high doses. Similarly, the OHB increased soil microbial activity by ～68 and ～72 %, respectively, for the low and high doses. AMF root colonization, spore number, and total glomalin-related soil protein (GRSP) production increased by ～3, ～2, and ～3 times, respectively, in soils treated with 1 % OHB. Despite being a metalophyte, O. picensis could not uptake Cu efficiently. Root and shoot Cu concentrations decreased or changed insignificantly in most BC treatments.

Conclusions

The results show that the BCs decreased bioavailable Cu, decreased Cu uptake by O. picensis, improved habitat for microorganisms, and enhanced plant growth in Cu-contaminated soil. This suggests that biochars may be utilized to remediate Cu-contaminated soils.

     

Culture-based and culture-independent assessment of the impact of mixed and single plant treatments on rhizosphere microbial communities in hydrocarbon contaminated flare-pit soil

Phytoremediation is a novel treatment option for weathered, hydrocarbon contaminated, flare-pit soil in prairie ecosystems. The remediation potential of six different naturalized prairie plants was assessed by examining their impact on the degradation potential of indigenous bacterial communities. Culture-based and culture-independent microbiological methods were used to determine if mixed plant treatments stimulate different microbial communities and catabolic genotypes in comparison to individual plant species that comprise the mix. DGGE analysis of PCR-amplified 16S rRNA genes revealed that alfalfa (Medicago sativa) had a dominant effect on the structure of rhizosphere microbial communities in mixed plant treatments, stimulating relative increases in specific Bacteroidetes and Proteobacteria populations. Alfalfa and mixes containing alfalfa, while supporting 100 times more culturable PAH degraders than other treatments, exhibited only 10% TPH reduction, less than all planted treatments except perennial rye grass (Lolium perenne). Total petroleum hydrocarbon (TPH) reduction was greatest in single-species grass treatments, with creeping red fescue (Festuca rubra) reducing the TPH concentration by 50% after 4.5 months. Overall TPH reduction throughout the study was positively correlated (p<0.001) to culturable n-hexadecane degraders.     

Beneficial effects of earthworms and arbuscular mycorrhizal fungi on establishment of leguminous trees on Pb/Zn mine tailings

Planting trees to stabilize metalliferous mine tailings is a widely used form of land reclamation although substantial soil amendment is invariably required, both to improve the physico-chemical status of the tailings and to ameliorate toxicity prior to planting. Here, we report a glasshouse study of the combined effects of burrowing earthworms (Pheretima guillelmi) and arbuscular mycorrhizal fungi (Glomus spp., AMF) on establishment of a naturally invasive, woody, nitrogen-fixing legume, Leucaena leucocephala, on topsoil-amended Pb/Zn mine tailings. AMF provided the most effective preliminary inoculant, improving N, P and K uptake, but earthworms had more influence improving N nutrition. In most cases, the combined effects of AMF and earthworms were additive and proved to be beneficial to plant growth, plant nutrition and for protection against uptake of toxic metals. AMF influenced metal uptake more than earthworms, but together they reduced mobility of Pb and Zn in soil by as much as 25%. Some minor but significant negative interactions were also evident; for example, earthworms enhanced soil microbial activity but inhibited the beneficial effects of AMF on N₂-fixation. We argue that increased attention to ecological interactions in soil could reduce costs and improve the efficacy of restoring a vegetation cover to land impacted by contaminated spoils.     

Perennial plant species from semiarid gypsum soils support higher AMF diversity in roots than the annual Bromus rubens

The arbuscular mycorrhizal fungi (AMF) communities composition regulate plant interactions and determine the structure of plant communities. In this study we analysed the diversity of AMF in the roots of two perennial gypsophyte plant species, Herniaria fruticosa and Senecio auricula, and an annual herbaceous species, Bromus rubens, growing in a gypsum soil from a semiarid area. The objective was to determine whether perennial and annual host plants support different AMF communities in their roots. The roots were analysed by nested PCR, cloning, sequencing of the ribosomal DNA small subunit region and phylogenetic analysis. Twenty AMF sequence types, belonging to the Glomus group A, Glomus group B, Diversisporaceae, Acaulosporaceae, Archaeosporaceae and Paraglomeraceae, were identified. Both gypsophyte perennial species, H. fruticosa and S. auricula had different compositions of the AMF community and higher diversity than B. rubens. This annual plant species shared the full composition of its AMF community with both perennial plant species. Seasonal variations in the colonisation of AM fungi could explain the observed differences in AMF community composition, but this is still a working hypothesis that requires the analysis of further data obtained from a higher number of both annual and perennial plant species in order to be fully tested.