Plant--rhizosphere-microflora association during phytoremediation of PAH-contaminated soil

The capability of plants to promote the microbial degradation of pollutants in rhizosphere soil is a principal mechanism of phytoremediation of PAH-contaminated soil. The formation of a specific rhizosphere microbocenosis with a high degradative potential toward contaminants is largely determined by plant species. The comparative PAH-degradation in unplanted soil and in soil planted with reed (Phragmites australis) and alfalfa (Medicago sativa) was studied in pot experiments during 2 years. Both alfalfa and reed successfully remediated contaminated soil by degrading 74.5 and 68.7% of PAHs, respectively. The study of the rhizosphere, rhizoplane, and unplanted-soil microflora in experimental pots showed that alfalfa stimulated the rhizosphere microflora of PAH-contaminated soil more effectively than did reed. Alfalfa clearly enhanced both the total number of microorganisms (1.3 times, according to fluorescence microscopy data) and the rate of the PAH-degrading population (almost seven times, according to plate counting). The degradative potential of its rhizosphere microflora toward PAHs was higher than the degradative activity of the reed rhizosphere. This study provides relevant information for the successful application of alfalfa to phytoremediate PAH-contaminated soil.     

Studies of the Efficacy of Alfalfa and Reed in the Phytoremediation of Hydrocarbon-Polluted Soil

The efficacy of plants as means of decontaminating hydrocarbon-polluted soil has been studied. Ditch reed (Phragmites australis) and alfalfa (Medicago sativa) markedly intensified processes of pollutant destruction, the effect being particularly pronounced in the case of polycyclic aromatic hydrocarbons. Comparative analysis of microflora in soils (including those devoid of plants and rhizosphere) demonstrated that, in addition to preventing a pollutant-induced decrease in the amount of heterotrophic microorganisms, the plants stimulated their development, significantly increasing the population of degraders. Effects of plants on major physiological groups of soil microorganisms under conditions of pollution were ambiguous. The rhizosphere microbial consortium of alfalfa was less susceptible to effects of pollutants than that of reed.     

Efficiency of alfalfa and reed in the phytoremediation of hydrocarbon polluted soil

The efficacy of plants as means of decontaminating hydrocarbon-polluted soil has been studied. Ditch reed (Phragmites australis) and alfalfa (Medicago sativa) markedly intensified processes of pollutant destruction, the effect being particularly pronounced in the case of polycyclic aromatic hydrocarbons (PAHs). Comparative analysis of microflora in soils (including those devoid of plants and rhizosphere) demonstrated that, in addition to preventing the pollutant-induced decrease in the amount of heterotrophic microorganisms, the plants stimulated their development, significantly increasing the population of destructors. Effects of plants on major physiological groups of soil microorganisms under conditions of pollution were ambiguous. The rhizosphere consortium of alfalfa was less susceptible to effects of pollutants than that of reed.     

接种内生降解菌Stenotrophomonas pavanii DJL-M3对多菌灵胁迫下水稻根际微生态的影响

内生降解菌定殖可促进水稻中农药等有机污染物的降解代谢,研究功能内生菌对农药暴露下水稻根际微生态的影响,可为利用植物-微生物互作调控农作物农药残留及修复农田生态环境污染提供科学依据。以水稻根际土壤中的蚯蚓、土壤酶和微生物群落为研究对象,分析接种内生菌Stenotrophomonas pavanii DJL-M3对水稻根际微生态响应多菌灵胁迫的影响。结果表明：多菌灵暴露导致水稻根际土壤过氧化氢酶活性增强,脲酶和蔗糖酶活性被抑制;多菌灵污染可对水稻根际周围的蚯蚓造成氧化损伤,致使其体内丙二醛累积并诱导超氧化物歧化酶和乙酰胆碱酯酶过表达;多菌灵残留显著降低水稻根际土壤微生物群落的多样性与碳源代谢活性。接种内生降解菌S.pavanii DJL-M3促进了水稻根际残留多菌灵的降解,缓解根际土壤微生物与蚯蚓所受胁迫压力,显著提高了土壤脲酶、蔗糖酶活力以及蚯蚓的存活率,并有效提升了水稻根际微生物群落的代谢活性与多样性。因此,接种内生降解菌S.pavanii DJL-M3有助于多菌灵残留污染下稻田土壤生态环境的恢复。     

Isolation and characterization of different plant associated bacteria and their potential to degrade polychlorinated biphenyls

In our experiments the effect of different plants on microbial activities resulting in degradation and PCB removal from long-term contaminated soil was evaluated. Total bacteria and bacteria representing the dominating microflora within rhizosphere of individual plant species – tobacco (Nicotiana tabacum), black nightshade (Solanum nigrum), horseradish (Armoracia rusticana) and goat willow (Salix caprea) planted in PCB contaminated soil as well as from the same, but non-vegetated PCBs soil, were isolated and biochemically characterized. PCB bacterial degraders, stimulated by root exudates of individual plants, were detected after isolation from rhizosphere soil and precultivation on minimal medium with biphenyl as the sole carbon source. Detection of BphA1 gene (first gene of bacterial aerobic PCB degradative pathway) in genomes of rhizosphere microorganisms was performed by nested PCR technique using previously designed specific primers. Rhizosphere of individual plants contained different bacterial species, mostly gram-negative non-fermenting bacteria of Pseudomonas, Agrobacterium, Ochrobactrum and other species. Gene BphA1 was identified in genome of only several of them. From tested species, S. caprea and A. rusticana have shown to be promising candidates for rhizoremediation purposes.     

白马雪山云南黄芪与灰毛康定黄芪根际微生物物种多样性及抗生物膜活性菌株筛选

【背景】细菌生物膜是造成病原菌耐药性增强和持续感染的主要因素,但目前尚无针对抗菌膜的特效药物。特境植物根际微生物可产生大量具有提高宿主免疫功能的活性成分,极具抗生物膜药源开发潜力。【目的】了解滇西北高寒特境白马雪山分布的云南黄芪与灰毛康定黄芪植物根际微生物的物种多样性,并对可培养菌株进行抑菌与抗生物膜活性筛选。【方法】采用宏基因组技术结合传统微生物培养方法,对采自我国云南迪庆藏族自治州德钦县白马雪山的云南黄芪与灰毛康定黄芪的根际微生物进行物种多样性研究,并通过“孔板法”测定其可培养菌株发酵液乙酸乙酯粗浸膏的抗菌、抗生物膜活性。【结果】宏基因组测序结果显示,云南黄芪根际土壤样本中的微生物来自6门7纲8目8科9属10种,其中栖热菌属为优势菌群;灰毛康定黄芪根际土壤样本中的微生物来自6门8纲10目11科14属15种,其中慢生根瘤菌属为优势菌群。通过纯培养共获得145株可培养菌株,包括112株细菌和33株真菌。其中,云南黄芪根际细菌59株,共计16属35种,优势属为假单胞菌属和链霉菌属;根际真菌19株,共计4属5种,优势属为曲霉属;灰毛康定黄芪根际细菌53株,归属于16属29种,优势属为芽孢杆菌属与寡养单胞菌属;根际真菌14株,归属于3属4种,优势属为曲霉属。从不同种水平上选择51株细菌和7株真菌为代表菌株进行抗生素药源评估,发现5株细菌及1株真菌发酵液的乙酸乙酯粗浸膏具有中等至较强的抗革兰阳性菌活性,而且其中4株具有抗MRSA生物膜活性,最终确定了链霉属放线菌Streptomyces fulvissimus KTA1和曲霉属真菌Aspergillus fumigatus YNF5为潜力活性菌株。【结论】首次报道了滇西北地区高寒特境黄芪属植物根际微生物具有较好的物种多样性,而且具有一定的抗生素药用资源开发潜力。本研究对滇西北高寒特境特色植物来源的微生物资源开发利用与保护具有重要的借鉴意义。     

不同时期艾比湖湿地盐角草群落土壤固氮微生物的多样性分析

【目的】研究新疆艾比湖湿地不同季节盐角草根际和非根际土壤固氮微生物的多样性和丰富度与环境因子的相关性,以期探究在荒漠化和盐渍化不断严重的艾比湖湿地中随着季节变化的固氮微生物群落对恢复生态功能起到的潜在作用,为后续的湿地保护和退化恢复工作提供理论支持和数据基础。【方法】应用Illumina HiSeq PE250测序技术,分析6个土壤样本固氮微生物的多样性,结合相关的理化因子并利用RDA分析法探究土壤理化性质和固氮微生物菌落结构及丰富度的相关性。【结果】艾比湖湿地盐角草植物根际土壤的固氮微生物多样性高于非根际土壤,7月的土壤固氮微生物多样性高于10月和4月的土壤。土杆菌属(Geobacter)、假单胞菌属(Pseudomonas)、固氮菌属(Azotobacter)和慢生根瘤菌属(Bradyrhizobium)等为盐角草根际和非根际土壤中的共同优势菌属。这些固氮微生物优势菌属隶属于变形菌门(Proteobacteria)和蓝藻门(Cyanobacteria),且相对丰富度占比为85%和10%,其余各菌门共占比较少,仅为5%。土壤中固氮微生物的优势菌群与碱解氮(AN)、全氮(TN)、速效钾(AK)和有效磷(TP)呈显著相关。【结论】随着时间的推移土壤样本中固氮微生物的多样性和群落结构也发了改变,同一时期植物根际与非根际土壤中固氮微生物的群落结构并不相同。土壤的环境因子与固氮细菌的群落结构和丰富度的相关性研究可以为艾比湖湿地的退化恢复提供数据基础和理论支持。     

深松对乌拉尔甘草根际土壤养分以及微生物群落功能多样性的影响

通过大田试验和室内分析相结合,研究了深松对乌拉尔甘草根际土壤养分和微生物群落功能多样性的影响,以期为乌拉尔甘草人工种植地土壤耕作措施优化和土壤环境改良提供依据。结果表明,与未深松(常规耕作)处理相比,深松处理对乌拉尔甘草根际土壤0—20 cm耕层土壤养分含量无显著性影响,可显著提高乌拉尔甘草根际土壤20—40 cm耕层有机质、全氮、全磷和全钾的含量,分别提高了60.8%、65.3%、48.9%和86.8%;明显增加了0—20 cm和20—40 cm耕层细菌、真菌和放线菌的数量(P0.05),3种类型的微生物数量均呈现出上层大于下层,深松大于未深松的变化趋势。在156 h的微生物温育期内,深松处理下不同土层的平均颜色变化率(AWCD)均显著高于未深松处理,并显著提高了AWCD的利用率(72 h,P0.05),较未深松分别提高了35.5%和130.8%。与未深松处理相比,深松处理显著提高了土壤微生物的多样性指数(H、S、D)。主成分分析(PCA)表明,深松优化了乌拉尔甘草根际土壤微生物的群落组成;聚合物、羧酸类化合物、氨基酸和碳水化合物是深松处理下根际土壤微生物利用的主要碳源。总而言之,深松处理显著提高乌拉尔甘草根际土壤养分含量、微生物数量和微生物多样性指数,改变了微生物群落功能多样性,造成这种差异的主要原因可能是深松改变了土壤耕层结构,改善了微生物的生存环境。因此,深松对乌拉尔甘草人工种植地土壤质量的改良有积极作用。     

硬化地表对油松和白蜡树下非根围及根围土壤微生物量碳氮的影响

硬化地表是城市化发展的重要特征,为了明确硬化地表下土壤环境的变化,以北京典型绿化树油松和白蜡为试验材料,设置透水硬化地表(PP)、不透水硬化地表(IPP)和自然地表(Ctr)3个水平的地表类型,探讨硬化地表对非根围和根围土壤微生物量碳(MBC)、氮(MBN)的影响。结果表明,与对照(Ctr)相比,PP和IPP显著降低了油松和白蜡树下非根围土壤MBC、MBN、MBC/OC(微生物量碳/有机碳)和MBN/TN(微生物量氮/全氮)(P<0.05),并显著降低了油松树下根围土壤MBN/TN(P<0.05);PP显著降低了白蜡树下根围土壤MBN、MBC/OC、MBN/TN和油松树下根围土壤MBC(P<0.05)。硬化地表引起的土壤MBC、MBN的变化与土壤全碳、全氮、有机碳的变化显著正相关(P<0.05),MBN的变化与含水量呈显著负相关(P<0.05)。可见,硬化地表不利于土壤微生物的生长,并且在非根围土壤中表现更为明显,这种不利影响将可能进一步影响城市绿地的养分循环、树木生境和生态系统服务功能。     

高寒特境中甸黄芪植物根际微生物物种多样性及其抗生物膜活性成分

滇西北高寒地区分布着丰富的黄芪属植物资源，该属植物“根际效应”明显，其根际微生物极具抗菌药用资源研究价值。【目的】认知滇西北高寒特境中甸黄芪根际微生物的物种多样性，探究其可培养菌株次生代谢产物的化学多样性及抗菌、抗生物膜活性。【方法】采用宏基因组和微生物纯培养方法对中甸黄芪植物根际微生物进行物种多样性分析，同时采用高效液相色谱（high performance liquid chromatography，HPLC）、超高效液相色谱-质谱联用法（ultra-performance liquid chromatography-mass spectrometry，UPLC-MS）结合“微量肉汤稀释法” “孔板法”等多级联合筛选策略综合评估可培养菌株的抗菌活性药源研究价值。【结果】对中甸黄芪根际土壤样本的微生物分类操作单元（operational taxonomic units，OTU）进行分类注释，得到22门54纲105目187科316属856种微生物，其中优势菌群为慢生根瘤菌属。纯培养共获得27属54种95株可培养菌株，包括20属33种54株细菌和7属21种41株真菌，优势属分别为芽孢杆菌属和青霉属。其中，1株细菌Pseudomonas tolaasii ZTB4和3株真菌Aspergillus tabacinus ZNF17、Lecanicillium aphanocladii ZNF15、Umbelopsis nana ZTF31的次生代谢产物具有广谱抗菌活性。同时，菌株ZTB4和ZNF17的次生代谢产物也显示出优秀的抗耐甲氧西林金黄色葡萄球菌（methicillin-resistant Staphylococcus aureus，MRSA）生物膜活性，并已验证这2株菌株的主要活性成分分别为环脂肽类与黄酮类。【结论】中甸黄芪植物根际微生物物种多样性较为丰富，其可培养菌株次生代谢产物有较好的化学多样性和抗菌、抗生物膜活性。研究结果为我国特境特色微生物药用资源的开发利用提供理论依据。     

Manganese reduction in the rhizosphere of mycorrhizal and nonmycorrhizal maize

The influence of rhizosphere microorganisms and vesicular-arbuscular (VA) mycorrhiza on manganese (Mn) uptake in maize (Zea mays L. cv. Tau) plants was studied in pot experiments under controlled environmental conditions. The plants were grown for 7 weeks in sterilized calcareous soil in pots having separate compartments for growth of roots and of VA mycorrhizal fungal hyphae. The soil was left either uninoculated (control) or prior to planting was inoculated with rhizosphere microorganisms only (MO-VA) or with rhizosphere microorganisms together with a VA mycorrhizal fungus [Glomus mosseae (Nicol and Gerd.) Gerdemann and Trappe] (MO+VA). Mycorrhiza treatment did not affect shoot dry weight, but root dry weight was slightly inhibited in the MO+VA and MO-VA treatments compared with the uninoculated control. Concentrations of Mn in shoots decreased in the order MO-VA > MO+VA > control. In the rhizosphere soil, the total microbial population was higher in mycorrhizal (MO+VA) than nonmycorrhizal (MO-VA) treatments, but the proportion of Mn-reducing microbial populations was fivefold higher in the nonmycorrhizal treatment, suggesting substantial qualitative changes in rhizosphere microbial populations upon root infection with the mycorrhizal fungi. The most important microbial group taking part in the reduction of Mn was fluorescent Pseudomonas. Mycorrhizal treatment decreased not only the number of Mn reducers but also the release of Mn-solubilizing root exudates, which were collected by percolation from maize plants cultivated in plastic tubes filled with gravel quartz sand. Compared with mycorrhizal plants, the root exudates of nonmycorrhizal plants had two fold higher capacity for reduction of Mn. Therefore, changes in both rhizosphere microbial population and root exudation are probably responsible for the lower acquisition of Mn in mycorrhizal plants.     

云南两个花魔芋主产区软腐病害植株腐烂球茎中的菌群组成及特征

【目的】软腐病是侵染魔芋的主要病害,其危害性严重,广泛传播会导致花魔芋绝产,尚无有效防控措施。魔芋软腐病的发生及暴发性传播与病原菌及其菌群有较大相关性。本研究旨在明确云南2个主产区的软腐病害花魔芋球茎及其根际土壤中的主要致病菌和优势微生物种类,分析其菌群结构特征,从而为花魔芋软腐病害的防控提供支撑。【方法】研究采集云南富源和永平2个产区的花魔芋软腐病样品,应用Illumina NovaSeq 6000测序平台进行微生物宏基因组测序和分析。同时采用选择性培养基、多级纯化培养技术以及电镜超微形态解析,分别对病害腐烂球茎中的致病菌及优势菌类进行分离鉴定和观察验证。【结果】两个花魔芋主产区软腐病害植株球茎及土壤中的微生物都非常丰富,共检出107门2 502属15 721种微生物。这2个产区的花魔芋软腐病害主要致病菌均为胡萝卜软腐坚固杆菌(Pectobacterium carotovorum),此病原菌与嗜麦芽寡养单胞菌(Stenotrophomonas maltophilia)的优势生长是2个产区软腐病害植株腐烂球茎中菌群的主要特征。此外,同产区的病害组织与土壤样品之间的菌群组成差异较大,但这2类样品中的优势菌群组成的区域性差异较小。【结论】两个花魔芋主产区软腐病害球茎组织中菌群与该区土壤菌群的相关性较低,土壤菌群区域性差异比相应的病害组织菌群区域性差异要大。因此,主要病原菌和共生菌的优势生长突破了产地差异影响,成为了病害组织菌群的主要特征,使得2个主产区软腐病害花魔芋球茎中的微生物生态系统具有高度相似性。     

高寒草甸黄帚橐吾种群根际/非根际土壤可培养微生物群落特征

黄帚橐吾（Ligularia virgaurea）是高寒草甸常见的毒杂草,被认为是指示一个地区草地植被退化的重要物种,研究其根际/非根际土壤微生物在不同海拔梯度上的群落特征具有重要意义。以甘南州高寒草甸不同海拔梯度黄帚橐吾根际/非根际土壤可培养微生物为研究对象,采用稀释涂布平板法和最大可能数法（MPN）测定了土壤微生物的数量及土壤理化因子的变化。结果表明：细菌在微生物总数中占比最大,根际微生物数量随海拔升高呈先增加后减小的变化,非根际则表现为递增的趋势,微生物功能群在根际和非根际土壤中均逐渐增加;根际土壤的微生物和功能群数量均高于非根际土壤。RDA分析发现,土壤温度、有机碳、电导率、pH、全氮、全磷、速效氮及脲酶对根际/非根际土壤微生物数量及功能群变化影响较大。通径分析可知：根际土壤中,细菌和真菌受速效氮和有机碳影响较大,放线菌主要受土壤温度和电导率的影响;根际土壤固氮菌和氨化细菌决策系数速效氮 > 有机碳 > 全氮;根际和非根际土壤中硝化细菌的影响因子各不相同,根际土壤决策系数最大和最小分别为全磷和全氮,非根际则是pH和脲酶。     

柽柳根际一株盐单胞菌Bachu 26的分离、鉴定及其盐胁迫下的促生作用研究

盐渍化是世界性的土壤问题,植物促生根际细菌(plant growth-promoting rhizobacteria,PGPR)在盐碱地改良和促进植物生长方面具有独特优势。柽柳是典型的盐生植物,筛选其根际微生物并研究其促生效果与促生机制,以此开发微生物菌肥,具有重要的应用价值。【目的】筛选耐盐碱植物柽柳的根际微生物,对其基本特性、耐盐碱能力、促生功能及促生效果进行评估。【方法】从新疆巴楚境内野生柽柳根际土壤中筛选出一株耐盐碱细菌菌株Bachu 26;通过形态学观察、生理生化特性测定和16S rRNA基因序列分析,对该菌株进行鉴定;利用不同盐浓度(0%–20%)和不同pH(7.0–13.0),对菌株Bachu 26的耐盐耐碱能力进行测定;采用多种功能鉴定培养基测定其促生功能,并对生长素吲哚乙酸(indole-3-acetic acid, IAA)进行定量测定;通过二分格培养皿实验验证菌株产生挥发性酸性物质的能力;在普通培养皿上将拟南芥幼苗与菌株Bachu 26共培养,分析菌株对拟南芥幼苗的促生作用;在二分格培养皿上将拟南芥与Bachu 26隔离培养,分析菌株产生的挥发性酸性物质对拟南芥幼...     

Two Invasive Plants Alter Soil Microbial Community Composition in Serpentine Grasslands

Plant invasions pose a serious threat to native ecosystem structure and function. However, little is known about the potential role that rhizosphere soil microbial communities play in facilitating or resisting the spread of invasive species into native plant communities. The objective of this study was to compare the microbial communities of invasive and native plant rhizospheres in serpentine soils. We compared rhizosphere microbial communities, of two invasive species, Centaurea solstitialis (yellow starthistle) and Aegilops triuncialis (barb goatgrass), with those of five native species that may be competitively affected by these invasive species in the field (Lotus wrangelianus, Hemizonia congesta, Holocarpha virgata, Plantago erecta, and Lasthenia californica). Phospholipid fatty acid analysis (PLFA) was used to compare the rhizosphere microbial communities of invasive and native plants. Correspondence analyses (CA) of PLFA data indicated that despite yearly variation, both starthistle and goatgrass appear to change microbial communities in areas they invade, and that invaded and native microbial communities significantly differ. Additionally, rhizosphere microbial communities in newly invaded areas are more similar to the original native soil communities than are microbial communities in areas that have been invaded for several years. Compared to native plant rhizospheres, starthistle and goatgrass rhizospheres have higher levels of PLFA biomarkers for sulfate reducing bacteria, and goatgrass rhizospheres have higher fatty acid diversity and higher levels of biomarkers for sulfur-oxidizing bacteria, and arbuscular mycorrhizal fungi. Changes in soil microbial community composition induced by plant invasion may affect native plant fitness and/or ecosystem function.     

赤杨对辽东落叶松人工林土壤氨基糖积累的影响

微生物残留物是土壤稳定性碳库的重要组成部分,然而其对固氮树种的响应还不清楚。以辽东山区日本落叶松(Larix kaempferi)人工纯林和落叶松-赤杨混交林为研究对象,以氨基糖作为微生物残留物的生物标识物,研究了赤杨对落叶松人工林根际和非根际土壤氨基糖积累的影响。结果表明,混交林中落叶松根际和非根际各氨基糖单体含量均显著高于纯林,说明赤杨引入有利于土壤微生物残留物的积累。其中,混交林落叶松根际及非根际土壤氨基糖葡萄糖含量分别比纯林高出99.5%(P0.01)和154%(P0.01);胞壁酸含量分别比纯林高出66.1%(P0.01)和132.3%(P0.01)。赤杨引入对氨基葡萄糖/胞壁酸比值的影响不显著,但显著增加氨基糖对土壤有机碳的贡献。冗余度分析表明全氮是驱动土壤中氨基糖发生变化的主要因子。表明赤杨引入显著提高微生物固持的土壤碳库和有机碳稳定性,这对落叶松人工林合理经营具有重要意义。     

Effects of inorganic amendments (N,P and K) to soil on the rhizosphere microflora of antirrhinum plants infected withVerticillium dahliae Kleb

Summary A study of the inorganic amendments (N, P and K) to soil, and their effect on the rhizosphere microflora, as well as their relation to the control of wilt of antirrhinum plants caused byVerticillium dahliae Kleb. was done. Ammonium sulphate was the only chemical found to be significantly inhibitory toV. dahliae in vitro. Soil amendments (NPK) affected the rhizosphere microorganisms of the antirrhinum plants. Higher concentration of the chemicals were phytotoxic. It was further observed that ammonium sulphate, and the combined chemicals (NPK 25%) in soil delayed the senescence in healthy plants, suggests that chemical fertilisers affected the host plants directly. Addition of ammonium sulphate (0.25%), calcium nitrate (0.25%, 0.5%) combined NPK (0.25%) to soil caused considerable reduction in disease severity. It is assumed that this reduction may be caused by the (1) fungitoxic nature of the chemicali.e. ammonium sulphate, (2) antagonistic environment for the pathogen in the rhizosphere was boostedi.e. where calcium nitrate was added as soil amendments and (3) reduction in disease severity in soil-amended with combined NPK, may be due to the fact that antagonistic actinomycete population was boosted in the rhizosphere.     

Quantification of the geocarposphere and rhizosphere effect of peanut (Arachis hypogaea L.)

Roots and pods of field-grown peanut (groundnut) (Arachis hypogaea L.) were sampled at the R3, R5, and R7 developmental stages and examined in comparison to root- and pod-free soil for microbial population densities to assess the geocarposphere and rhizosphere effects. G/ S (no. geocarposphere microorganisms/no. soil microorganisms) and R/S (no. rhizosphere microorganisms/no. soil microorganisms) ratios were calculated for total fungi,Asperigillus flavus, spore-forming bacilli, coryneform bacteria, fluorescent pseudomonads, and total bacteria isolated on low- and high-nutrient media. A clear geocarposphere effect was evidenced by increased population densities of bacteria and fungi associated with developing pods compared to soil. G/S and R/S ratios were generally greater than 1.0 for all groups of microorganisms except bacilli. G/S ratios were greater for total bacteria than for total fungi at two of the three sample times, suggesting that bacteria were stimulated more than fungi in the zone around developing pods. In contrast, R/S ratios, were higher for total fungi than for total bacteria at two of three sample times. The preferential association of fungi and bacteria with early developmental stages of the pod indicates that some microorganisms are particularly well adapted for colonization of the peanut geocarposphere. These microorganisms are logical candidates for evaluation as biological control candiates forA. flavus.     

田菁根际促生菌的筛选及其促生耐盐效果

【目的】为探究盐生植物田菁及其根际功能微生物改良盐碱地的效果,本研究从黄河三角洲盐碱区田菁根际土壤中分离促生菌,并明确其耐盐促生效果。【方法】采用选择培养方法从田菁根际土壤中分离固氮菌、解磷菌以及解钾菌,并进行16S rRNA分子生物学鉴定。之后对菌株的耐盐及促生特性进行测定,筛选性状优良菌株进行玉米促生作用研究。【结果】共分离得到105株根际促生菌,其中N102兼具多种促生特性且耐盐性达15%。田菁种子发芽试验表明,N102可显著提高田菁发芽率(47%,P<0.05)、芽长(48.5%,P<0.05)和根长(60%,P<0.05);玉米盆栽试验结果表明,N102对盐胁迫下玉米的株高、根长、叶绿素含量、地上部干重以及根干重具有显著的促进作用。经系统发育分析,N102与Enterobacter soli ATCC BAA-2102 (NR117547)序列相似度为99.30%,鉴定属于Enterobacter属。【结论】菌株N102具有多种植物促生耐盐特性,具有开发成有效促进盐碱地作物生长的微生物肥的良好前景。     

溶磷细菌和丛枝菌根真菌接种对南方红豆杉生长及根际微生物和土壤酶活性的影响

以南方红豆杉实生苗为材料,采用盆栽实验探讨了高效溶磷细菌草木樨中华根瘤菌(Sinorhizobium meliloti)CHW10B与丛枝菌根真菌缩球囊霉(Glomus constrictum)单独和双接种条件下,其植株生长、根际土壤可培养微生物数量、土壤酶活和土壤微生物功能多样性变化,在微生态水平揭示接种对南方红豆杉生长的影响及其机制。结果表明:(1)各接种处理对南方红豆杉幼苗均有促生长作用,接种处理苗高、地径和生物量均较对照显著增加,并以双接种促进效果最好。(2)各接种处理提高了南方红豆杉根际土壤可培养细菌、真菌和放线菌含量,增加了土壤微生物碳源利用率,改变了土壤中物种的丰富度和均一度,增加了土壤中的生物多样性。(3)各接种处理促进了南方红豆杉根际重要土壤酶(酸性磷酸酶、脱氢酶、转化酶)活力的增加,且双接种的促进作用最为明显。可见,溶磷细菌(草木樨中华根瘤菌CHW10B)和丛枝菌根真菌(缩球囊霉)具有协同作用,两者同时接种可显著提高南方红豆杉根际土壤微生物数量及土壤酶活力,提高土壤微生物碳源利用率和土壤肥力,增加土壤中的生物多样性,从而达到间接促进宿主植物南方红豆杉生长的目的。