Effect of rhizosphere on soil microbial community and in-situ pyrene biodegradation

To access the influence of a vegetation on soil microorganisms toward organic pollutant biogegration, this study examined the rhizospheric effects of four plant species (sudan grass, white clover, alfalfa, and fescue) on the soil microbial community and in-situ pyrene (PYR) biodegradation. The results indicated that the spiked PYR levels in soils decreased substantially compared to the control soil without planting. With equal planted densities, the efficiencies of PYR degradation in rhizosphere with sudan grass, white clover, alfalfa and fescue were 34.0%, 28.4%, 27.7%, and 9.9%, respectively. However, on the basis of equal root biomass the efficiencies were in order of white clover >> alfalfa > sudan > fescue. The increased PYR biodegradation was attributed to the enhanced bacterial population and activity induced by plant roots in the rhizosphere. Soil microbial species and biomasses were elucidated in terms of microbial phospholipid ester-linked fatty acid (PLFA) biomarkers. The principal component analysis (PCA) revealed significant changes in PLFA pattern in planted and non-planted soils spiked with PYR. Total PLFAs in planted soils were all higher than those in non-planted soils. PLFA assemblages indicated that bacteria were the primary PYR degrading microorganisms, and that Gram-positive bacteria exhibited higher tolerance to PYR than Gram-negative bacteria did.     

Effects of hydroxypropyl-β-cyclodextrin on pyrene and benzo[α]pyrene: bioavailability and degradation in sotil

Effect of hydroxypropyl-β-cyclodextrin (HPCD) on the bioavailability and biodegradation of the polycyclic aromatic hydrocarbons (PAHs) pyrene (PYR) and benzo[α]pyrene (BaP) in spiked soils was investigated in 14-week incubation experiments. To evaluate the effect of HPCD in soils with a different matrix, humic substance (HS) was added into soil samples. A 6-h Tenax TA extraction method was used to evaluate pollutants bioavailability. The biodegraded and extracted fractions were compared to evaluate the impact of HPCD on PAHs biodegradation. Results indicated positive effects of HPCD on fast desorption behaviours of PAHs. The biodegraded fraction was consistent with that of the extracted for PYR. However, in terms of BaP, the results were contrary which suggests that biological factors may be limiting factors for BaP pollution remediation. HS weakened the HPCD solubilisation effect while accelerated the decay of PYR and BaP, also implying that bioavailability was not the sole factor limiting PAH biodegradation. In addition, analysis of microbial communities demonstrated that HPCD inhibited the growth of some soil bacteria while HS promoted the evolution of some soil microorganisms. A limited population of hydrocarbon degrader populations led to observing incomplete PAH biodegradation even in the presence of HPCD.     

玉米修复芘污染土壤的初步研究

采用60d室内盆栽试验,研究了玉米CT38(ZEAMAYSL.)对多环芳烃芘污染土壤的修复作用.结果表明,无论种植玉米土P系列、无植物对照土M系列(无植物且添加叠氮化钠的灭菌土)和对照土W系列(无植物未灭菌土)中芘的可提取浓度都随着时间的推移逐渐减少,种植玉米加快了土壤中可提取态芘浓度的下降.在芘处理浓度为10—100mg.kg-1的污染土壤中,种植玉米CT38的土壤中芘的去除率达81.9%—89.3%,分别比无植物对照土M系列和对照W系列中芘的去除率高67.5%—70.9%和26.2%—47.0%.玉米也可积累少量芘,但积累量所占芘去除量的比例不足0.3%,植物吸收不是芘去除的主要机理.种植玉米增强了土壤中脱氢酶和脲酶等酶活性,从而促进了植物-根圈微生物体系对芘的生物降解.     

The effect of imazethapyr on soil microbes in soybean fields in northeast China

Large quantities of herbicides are used on agricultural soils, but the effects of herbicides on the structure of the soil microbial community have not been well investigated. In this study, soil from three soybean fields was investigated. The herbicide imazethapyr was applied in one year to soil 1 and in two sequential years to soil 2. Control soil received no imazethapyr. Microbial biomass and community structure were characterised using chloroform fumigation–extraction and phospholipid fatty acid (PLFA) determination. The imazethapyr residue was 1.62 μ g·kg^?1 in soil 1 and 1.79 μ g·kg^?1 in soil 2. The microbial biomass carbon and total PLFAs for soil 2 were much higher than for the other soils. PLFA profiles showed that fatty acids for Gram-negative and Gram-positive bacteria, as well as total bacteria and total fungi in soil 2 were higher than in other samples. Principal component analysis of the PLFAs showed that the structure of the microbial community differed substantially among the three different soybean field soils. Application of the herbicide imazethapyr to soybean fields clearly changed the soil microbial biomass and shifted the structure of the microbial community.     

多环芳烃污染土壤的微生物-紫花苜蓿联合修复效应

微生物-植物联合修复技术作为一种低耗高效的新型修复手段已经被广泛应用于有机污染土壤的修复领域并取得了较好的效果,新型生物资源的应用将推动该方法的进一步发展。本研究采用温室盆栽实验,以里氏木霉（Trichodermaressei FS10-C）、根瘤菌（Rhizobium meliloti）和紫花苜蓿（Medicago sativa L.）作为供试生物,设置添加灭活菌剂-无紫花苜蓿（CK）、添加灭活菌剂-种植紫花苜蓿（A）、接种木霉菌剂-种植紫花苜蓿（TA）、接种木霉菌根瘤菌复合菌剂-种植紫花苜蓿（TRA）4种处理,探究微生物-植物联合修复对多环芳烃（PAHs）污染土壤的生物修复效果及其微生态效应。结果表明,经过60 d的培养,微生物不仅促进了紫花苜蓿的生长,而且在紫花苜蓿的协同作用下进一步提高了土壤中PAHs降解率。TA处理中紫花苜蓿生物量增加了5.88%,而TRA处理进一步促进了紫花苜蓿的生长,其生物量增加了11.15%;A、TA和TRA处理下土壤中PAHs的降解率分别为17.02%、25.62%、32.93%,显著（p〈0.05）高于处理CK（5.67%）。此外,接种菌剂处理（TA、TRA）对土壤中高分子量PAHs具有更好的降解效果,A处理土壤中4-、5（＋6）环PAHs的降解率分别为18.13%、24.74%,TA处理为21.41%、28.34%,而TRA处理则为21.29%、30.11%。同时,紫花苜蓿能够通过其根际效应显著促进土壤微生物活性,相较于CK处理,A、TA、TRA处理土壤脱氢酶活性分别提高了33.20%、34.58%、32.65%,A、TA、TRA处理AWCD值和微生物群落多样性指数均显著（p〈0.05）高于CK。通过木霉、根瘤菌与紫花苜蓿联合作用不仅可以有效地降解土壤中的PAHs,而且能够恢复土壤微生物生态功能多样性和稳定性。因此,该方法是一种极具潜力的生物修复手段,具有广阔的市场应用前景。     

化学农药污染土壤植物修复中的环境化学问题

报道了利用植草修复受DDT，BHC和Dicofol污染的研究，讨论了化学农药污染土壤植物修复中,农药在植物中富集与在土壤中降解以及结合残留等环境化学问题。研究表明，在植物修复的过程中，通过草对农药吸收的途径而去除土壤中污染物的作用所作的贡献很小，植草的作用可能是通过草的根部向土壤释放酶和某些分泌物，从而激发土壤中微生物的活性，并加速农药生物降解作用的结果。草在不同土壤中修复能力的差异，可能与不同土壤中所存土著微生物的差异以及其活性受酶和某些分泌物所激发差异的结果。选择能使根际区产生强烈的生物降解作用的草品种，是利用草作为化学农药污染土壤修复的关键。土壤与植株中农药结合残留的形成可能是土壤中污染物消除的又一个重要因素。     

A simple approach to modeling microbial biomass in the rhizosphere

Microorganisms make an important contribution to the degradation of contaminants in bioremediation as well as in phytoremediation. An accurate estimation of microbial concentrations in the soil would be valuable in predicting contaminant dissipation during various bioremediation processes. A simple modeling approach to quantify the microbial biomass in the rhizosphere was developed in this study. Experiments were conducted using field column lysimeters planted with Eastern gamagrass. The microbial biomass concentrations from the rhizosphere soil, bulk soil, and unplanted soil were monitored for six months using an incubation–fumigation method. The proposed model was applied to the field microbial biomass data and good correlation between simulated and experimental data was achieved. The results indicate that plants increase microbial concentrations in the soil by providing root exudates as growth substrates for microorganisms. Since plant roots are initially small and do not produce large quantities of exudates when first seeded, the addition of exogenous substrates may be needed to increase initial microbial concentrations at the start of phytoremediation projects.     

Microbial community and functional genes in the rhizosphere of alfalfa in crude oil-contaminated soil

A rhizobox system constructed with crude oil-contaminated soil was vegetated with alfalfa (Medicago sativa L.) to evaluate the rhizosphere effects on the soil microbial population and functional structure, and to explore the potential mechanisms by which plants enhance the removal of crude oil in soil. During the 80-day experiment, 31.6% of oil was removed from the adjacent rhizosphere (AR); this value was 27% and 53%higher than the percentage of oil removed from the far rhizosphere (FR) and from the non-rhizosphere (NR), respectively. The populations of heterotrophic bacteria and hydrocarbon-degrading bacteria were higher in the AR and FR than in the NR. However, the removal rate of crude oil was positively correlated with the proportion of hydrocarbon-degrading bacteria in the rhizosphere. In total, 796, 731, and 379 functional genes were detected by microarray in the AR, FR, and NR, respectively. Higher proportions of functional genes related to carbon degradation and organic remediation, were found in rhizosphere soil compared with NR soil, suggesting that the rhizosphere selectively increased the abundance of these specific functional genes. The increase in water-holding capacity and decrease in pH as well as salinity of the soil all followed the order of AR>FR>NR. Canonical component analysis showed that salinity was the most important environmental factor influencing the microbial functional structure in the rhizosphere and that salinity was negatively correlated with the abundance of carbon and organic degradation genes.     

环毛蚓在高羊茅修复土壤菲污染过程中的作用

为了解土壤动物在植物修复多环芳烃类化合物过程中的作用,采用盆栽试验法,对比研究了蚯蚓（Pheretima sp．）活动对高羊茅（Festuca arundinacea）修复土壤菲污染的影响效应以及各种生物、非生物因子在植物修复菲污染过程中的作用。结果显示,在20．05-322．06mg·kg^-1菲污染水平范围内,与相同污染水平下无蚯蚓作用的菲污染土壤中生长的植株相比,蚯蚓活动促进修复植物高羊茅的生长：试验期间（72d）,修复植物的单株生物量增加9．74％～21．53％,根冠比增加17．26％～21．44％。添加蚯蚓72d后,种植高羊茅的菲污染土壤中,菲的去除率高达61．70％～88．78％,其平均去除率（77．38％）比无蚯蚓活动的土壤-植物系统中的（68．36％）提高了9．02％,比无植物生长的对照组土壤（22．57％）提高54．81％。各种生物（如植物代谢、植物积累、动物积累、微生物降解、植物．微生物交互作用等）、非生物（如渗滤、吸附、光解、挥发等）因子中,植物．微生物交互作用对菲去除的平均贡献率（47．81％）最为突出,比无蚯蚓活动时（42．08％）提高5．73％。说明蚯蚓活动可强化土壤．植物系统对土壤菲污染的修复作用。     

Changes in microbial community characteristics and soil organic matter with nitrogen additions in two tropical forests

Microbial communities and their associated enzyme activities affect the amount and chemical quality of carbon (C) in soils. Increasing nitrogen (N) deposition, particularly in N-rich tropical forests, is likely to change the composition and behavior of microbial communities and feed back on ecosystem structure and function. This study presents a novel assessment of mechanistic links between microbial responses to N deposition and shifts in soil organic matter (SOM) quality and quantity. We used phospholipid fatty acid (PLFA) analysis and microbial enzyme assays in soils to assess microbial community responses to long-term N additions in two distinct tropical rain forests. We used soil density fractionation and 13C nuclear magnetic resonance (NMR) spectroscopy to measure related changes in SOM pool sizes and chemical quality. Microbial biomass increased in response to N fertilization in both tropical forests and corresponded to declines in pools of low-density SOM. The chemical quality of this soil C pool reflected ecosystem-specific changes in microbial community composition. In the lower-elevation forest, there was an increase in gram-negative bacteria PLFA biomass, and there were significant losses of labile C chemical groups (O-alkyls). In contrast, the upper-elevation tropical forest had an increase in fungal PLFAs with N additions and declines in C groups associated with increased soil C storage (alkyls). The dynamics of microbial enzymatic activities with N addition provided a functional link between changes in microbial community structure and SOM chemistry. Ecosystem-specific changes in microbial community composition are likely to have far-reaching effects on soil carbon storage and cycling. This study indicates that microbial communities in N-rich tropical forests can be sensitive to added N, but we can expect significant variability in how ecosystem structure and function respond to N deposition among tropical forest types.     

Tree species and mycorrhizal associations influence the magnitude of rhizosphere effects

Previous research on the effects of tree species on soil processes has focused primarily on the role of leaf litter inputs. We quantified the extent to which arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) tree species influence soil microbial activity and nutrient availability through rhizosphere effects. Rhizosphere soil, bulk soil, and fine roots were collected from 12 monospecifc plots (six AM and six ECM tree species) planted on a common soil at the Turkey Hill Plantations in Dryden, New York. Rhizosphere effects were estimated by the percentage difference between rhizosphere and bulk soil samples for several assays. Rhizosphere effects on soil microbes and their activities were significant for ECM species but in only a few cases for AM species. In AM tree species, microbial biomass, net N mineralization, and phosphatase enzyme activity in the rhizosphere were 10-12% greater than in bulk soil. In ECM tree species, rhizosphere effects for microbial biomass, C mineralization rates, net N mineralization, and phosphatase activity were 25-30% greater than bulk soil, and significantly greater than AM rhizosphere effects. The magnitude of rhizosphere effects was negatively correlated with the degree of mycorrhizal colonization in AM tree species (r = -0.83) and with fine root biomass (r = -0.88) in ECM tree species, suggesting that different factors influence rhizosphere effects in tree species forming different mycorrhizal associations. Rhizosphere effects on net N mineralization and phosphatase activity were also much greater in soils with pH < 4.3 for both AM and ECM tree species, suggesting that soil pH and its relation to nutrient availability may also influence the magnitude of rhizosphere effects. Our results support the idea that tree roots stimulate nutrient availability in the rhizosphere, and that systematic differences between AM and ECM may result in distinctive rhizosphere effects for C, N, and P cycling between AM and ECM tree species.     

Microbial relationships in surface-mine revegetation

The establishment and interrelationships of microorganisms with soil and plant processes during reclamation are greatly influenced by the composition of the planting medium and vegetation practices. While in some instances the parent material may be used as the vegetation medium, the practice of topsoiling, particularly the direct haul method, may be beneficial in introducing microorganisms and improving the quality of the plant growth medium of spoils that are chemically or physically less desirable than the native soils. The influence of different vegetation types on soil development on surface mines may be a reflection of physioiogical differences that affect microbial development in the rhizosphere. Such differences include levels of carbohydrate translocated to the root system and/or released into the surrounding soil; the plant's effectiveness as a mycorrhizal host; and the rate of degradation of plant residues. It has become apparent that microbial interactions are an important part of plant and soil processes in reclamation. While some of the microorganisms important in plant growth and soil development can be introduced readily by management practices, the majority usually are disseminated by natural means and only gradually become a part of the microbial population. More research is needed on developing new methods or refining current procedures for early introduction of these microorganisms in reclamation practices.     

Microbial relationships in surface-mine revegetation

The establishment and interrelationships of microorganisms with soil and plant processes during reclamation are greatly influenced by the composition of the planting medium and vegetation practices. While in some instances the parent material may be used as the vegetation medium, the practice of topsoiling, particularly the direct haul method, may be beneficial in introducing microorganisms and improving the quality of the plant growth medium of spoils that are chemically or physically less desirable than the native soils. The influence of different vegetation types on soil development on surface mines may be a reflection of physioiogical differences that affect microbial development in the rhizosphere. Such differences include levels of carbohydrate translocated to the root system and/or released into the surrounding soil; the plant's effectiveness as a mycorrhizal host; and the rate of degradation of plant residues. It has become apparent that microbial interactions are an important part of plant and soil processes in reclamation. While some of the microorganisms important in plant growth and soil development can be introduced readily by management practices, the majority usually are disseminated by natural means and only gradually become a part of the microbial population. More research is needed on developing new methods or refining current procedures for early introduction of these microorganisms in reclamation practices.     

Comparison on bacterial community of rhizosphere and bulk soil of poplar plantation based on pyrosequencing北大核心CSCD

By the 454 pyrosequencing technology, this research compared the bacterial communities in poplar plantation rhizosphere and bulk soil for an accurate understanding of bacterial community colonization in the two soil environments. The species annotation showed that rhizosphere soil contained 145 bacterial genera and bulk soil contained 141 bacterial genera, with 8 common genera shared by both at a relative abundance of more than 4%. The 8 genera in common were Acidobacterium GP1, Acidobacterium GP3, Acidobacterium GP6, Gemmatimonas, Bradyrhizobium, Burkholderia, Streptomyces and Acidobacterium GP4. The relative abundance of the same bacterial community was significantly different between rhizosphere and bulk soil environments. Alpha diversity analysis showed that the bacterial community diversity of rhizosphere soil was higher than that of bulk soil, but the difference was not significant. The results of bacterial communities sorting could reflect the variation of soil bacterial communities from rhizosphere to the bulk and the spatial variation among different sampling points, indicating a contribution of about 21.2% variance of bacterial communities by the effect of rhizosphere. Beta diversity analysis showed great difference between rhizosphere and bulk soil samples in bacterial community composition. There were 15 genera specific to rhizosphere soil and 11 to bulk soil. The abundance of 23 genera, mainly cellulose degrading bacteria and nitrogen-fixing bacteria, changed significantly. Selectivity of root to rhizosphere microorganisms is an important mechanism leading to significant differences in the rhizosphere microbial community composition and structure, which may significantly impact the carbon and nitrogen cycles of the root-soil interface.     

土壤微生物生物量及多样性测定方法评述

土壤微生物作为土壤中重要的分解者,在养分的循环与转化中起着重要的作用。另外,由于其与土壤理化性质相比,对外界环境的变化更为敏感,因此,土壤微生物性质常被用作表征土壤质量的灵敏性指标,而土壤微生物生物量与微生物多样性是土壤微生物学研究中应用最广泛的指标。土壤环境复杂,微生物种类丰富多样,需要合适的研究方法才能真正打开土壤系统这个黑箱,自19世纪60年代以后,土壤微生物学在研究方法上取得了重要的进展,本文综述了微生物生物量及多样性的概念及微生物生物量和多样性研究方法的发展状况,重点就已有应用比较多的研究方法如测定微生物生物量的熏蒸法,测定微生物多样性的平板计数法、Biolog微平板计数法、磷脂脂肪酸法及分子生物学等研究方法进行了详细介绍及优缺点分析。结合现有微生物生物量及多样性的测定方法,在未来的研究中,一方面应该引入更多的新技术,发展新方法,以期探索更多的未知微生物种群;其次应该根据实验要求,完善和改进现有研究方法,使其更为统一和准确;再者,在微生物数据的分析上应该探索和借鉴更多的分析方法和手段,从而更深入更全面的解读实验当中所得到的微生物的信息。     

返青前后草地早熟禾草坪根际微生物区系动态

根际是土壤-植物生态系统物质及能量交换的活跃界面,根际微生物不仅直接影响植物对水分、养分的吸收,而且也同时影响植物对不良环境的抵抗能力。利用选择性培养基对草地早熟禾(PoapratensisL.)返青前后根际与非根际的细菌、真菌以及放线菌类群进行分离测数,拟从根际及非根际土壤微生物区系动态变化方面来阐述草地早熟禾返青前后其根际微生态的变化规律。结果表明:(1)草地早熟禾草坪的返青后,根际及非根际细菌、真菌数量明显增加,但放线菌数量呈减少趋势;(2)无论返青前后或者根际以及非根际,细菌的数量都占整个土壤微生物量的绝大部分,细菌数量的变化代表了整个微生物类群数量的变化趋势,使得草地早熟禾返青后根际土壤由"真菌型"向"细菌型"转化;(3)返青前后,各微生物类群都表现出明显的根际效应。     

洛克沙胂暴露胁迫对土壤微生物群落结构特征的影响

采用磷脂脂肪酸(phospholipid fatty acid,PLFA)方法,分析了洛克沙胂残留对土壤微生物群落结构的影响特征。结果表明,在整个采样周期中,每克土壤总PLFA含量在洛克沙胂胁迫影响下出现明显降低,且存在一定的剂量依赖效应。经主成分分析,第1周,洛克沙胂低浓度组(w=15 mg·kg-1)土壤微生物群落结构和对照组差异不明显,第2、3、5、8周,各组土壤微生物群落结构多样性的类型差异显著,其中高浓度组(w=150 mg·kg-1)与对照组差异最大。结果表明,洛克沙胂可致土壤微生物群落结构多样性改变,暴露浓度越高其作用越强。同时,洛克沙胂对土壤微生物群落结构多样性的影响还表现出时间差异,在暴露胁迫的后期(第5、8周),洛克沙胂的影响逐步减弱,可能与洛克沙胂在土壤中发生化学结构改变和降解有关。     

土壤和地下水中多环芳烃生物降解研究进展

多环芳烃是一类普遍存在于环境中的难降解的危险性"三致"有机污染物。受污染的土壤和地下水中的多环芳烃,生物降解是其归宿的主要途径。研究表明,对于土壤中低分子量多环芳烃类化合物,微生物一般以唯一碳源方式代谢;而大多数细菌和真菌对四环或四环以上的多环芳烃的降解作用一般以共代谢方式开始。文章重点论述了多环芳烃的来源、降解多环芳烃的微生物、生物降解机理、影响生物降解的因素以及生物修复方法。认为今后的研究方向是高分子量多环芳烃的降解机理与降解途径,基因工程技术在多环芳烃生物降解方面的应用,以及生物表面活性剂产生的机理及其在实际处理中的应用等。     

Cu、抗生素协同污染对土壤微生物活性的影响

随着畜禽养殖业的规模化发展,重金属和抗生素在土壤环境中协同污染的几率不断升高。为分析和评价重金属、抗生素协同污染对土壤微生物生态系统的影响,以Cu、磺胺甲基嘧啶为添加毒物,其中,Cu的添加质量分数为0、100、500mg·kg-1;磺胺甲基嘧啶的添加质量分数为0、5、25、50、100mg·kg-1,采用室内培养试验的方法研究分析了cu、磺胺甲基嘧啶协同污染对土壤微生物微生物基础呼吸、微生物量碳、微生物量氮、硝化势、尿酶以及脱氢酶等土壤微生物指标的影响。结果表明,与磺胺甲基嘧啶单独污染处理相比,在Cu的质量分数为100mg·kg。协同污染污染下土壤微生物呼吸,土壤微生物量碳、氮以及土壤尿酶等指标的活性均明显增加;即表明它们对Cu与磺胺甲基嘧啶的协同污染表现出不同程度的交互抗性;在cu的协同污染质量分数为500mg·kg-1,Cu与磺胺甲基嘧啶对土壤各微生物指标则基本表现为协同抑制作用;在不同剂量Cu的协同污染处理下,当磺胺甲基嘧啶处理质量分数≥10mg·kg-1时,各土壤微生物指标的活性随着其处理质量分数的增加而显著降低,表现出很好的剂量依赖效应。因此,低剂量的Cu．磺胺甲基嘧啶协同污染可能会诱导土壤微生物对二者产生交互抗性;而高剂量协同污染则对土壤微生物生态功能产生较为严重的协同抑制作用。     

Influence of inoculating earthworms on removal of pyrene in soils growing Festuca arundinacea

ABSTRACT

The aim of this study was to examine the potential of inoculating earthworms (Pheretima sp.) in order to enhance phytoremediation of polycyclic aromatic hydrocarbons (PAH) present in soils with the use of tall fescue (Festuca arundinacea). In particular, experiments with or without inoculating earthworms for removal of pyrene was investigated. Results showed that planting of F. arundinacea enhanced the removal of pyrene at initial content over 70 days approximately 54%–80% but only 12%–24% occurred in non-planted soils. After inoculating earthworms, the dissipation rates of pyrene in planted soils were increased up to 61%–86%, which was 6%–12% higher than those in corresponding soils without inoculating earthworms. Among all possible pathways, the contribution of plant--microbial interactions on removal of pyrene was predominant, either with (46%) or without inoculating earthworms (52%), is the primary mechanism of contaminant removal. Data suggest inoculating earthworms may be a feasible way for reinforcing removal of PAH in contaminated sites.