西北地区赤霞珠葡萄根际土壤中AM真菌的多样性

对西北地区5个酿酒葡萄赤霞珠（Vitis vinifera L. cv. Cabernet Sauvignon）葡萄园根际土壤060 cm土层的AM真菌空间分布进行了研究。结果表明,葡萄根系可形成丛枝菌根,且侵染率较高,最高达79%; 在西北地区的5个样地中共分离出AM真菌4属22种,其中球囊霉属（Glomus）15种,无梗囊霉属（Acaulospora）4种,盾巨孢囊霉属（Scutellospora）2种,巨孢囊霉属（Gigaspora）1种。5个样地孢子密度大小顺序为: 陕西泾阳（JY）＞山西永济（YJ）＞陕西杨凌（YL）＞宁夏银川（YC）＞甘肃莫高（MG）。各样地葡萄根际土壤中AM真菌种的丰富度不同,陕西泾阳地区最高; 分布于葡萄根际的AM真菌按种类多少排序的属依次是: 球囊霉属无梗囊霉属盾巨孢囊霉属巨孢囊霉属,球囊霉属占据的比例保持着绝对优势; 根内球囊霉、摩西球囊霉、地表球囊霉在不同样地中均为优势菌株,副冠球囊霉,集球囊霉,细凹无梗囊霉是多数样地中的稀有种类。研究表明,葡萄与AM真菌具有良好的共生关系,二者协同进化产生了具有生态环境特异性的菌根真菌多样性; 葡萄根际存在较为丰富的丛枝菌根真菌资源,可供进一步开发利用。     

毛乌素沙地典型克隆植物根际AM真菌多样性研究

为阐明毛乌素沙地3种典型克隆植物沙鞭[Psammochloa villosa(Trin.)Bor.]、羊柴(Hedysarum leaveMaxim)和油蒿(Artemisia ordosica Krasch.)根际AM真菌多样性,2006年的5月、7月、10月从毛乌素沙地选取东北缘的中国科学院植物研究所鄂尔多斯沙地草地生态研究站和西南缘的陕西榆林珍稀沙生植物保护基地两个样地,按0~10 cm、10~20 cm、20~30 cm、30~40 cm、40~50 cm 5个土层采集3种克隆植物根际土壤样品,研究了其根际AM真菌物种多样性和生态分布。在分离出的4属23种AM真菌中,球囊霉属(Glomus)15种,无梗囊霉属(Acaulospora)5种,巨孢囊霉属(Gigaspora)2种,盾巨孢囊霉属(Scutellospora)1种。摩西球囊霉(G.mosseae)是沙鞭根际的优势种,黑球囊霉(G.melanosporum)是3种克隆植物共同的常见种;不同属种的AM真菌生态分布亦存在差异。AM真菌孢子密度、种的丰度和物种多样性指数均表现为在研究站样地的羊柴根际最高。该研究结果表明,毛乌素沙地的3种典型克隆植物与AM真菌之间形成良好的共生关系,这对开发漠境AM真菌资源和利用菌根生物技术维护沙地生态系统结构的完整性具有重要意义。     

贵州务川汞矿区土壤丛枝菌根真菌多样性研究

对贵州务川汞矿区不同水平汞污染植物根际土壤丛枝菌根(Arbuscular Mycorrhizal,AM)真菌资源分布及多样性进行分析，结果发现：本研究选取的务川汞矿区3个样地土壤汞含量在94.1～268.0 mg/kg，远高于国家规定的土壤汞含量，汞污染极其严重。随着汞含量增加，AM真菌侵染率、孢子密度显著降低，AM真菌群落丰富度、多样性及均匀度均有所降低，但差异未达显著水平，而仍有部分对汞污染耐受性较强的AM真菌有较高的分布。另外，管柄囊霉属AM真菌在5个样品中均有较高丰度，球囊霉属AM真菌在火棘根际的相对丰度随着汞含量升高而升高，因此，火棘–管柄囊霉属AM真菌或火棘–球囊霉属AM真菌联合进行汞污染修复，有一定的应用价值。     

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。     

内蒙古盐碱土中AM真菌的多样性与分布

在内蒙古盐碱土13种主要植物分离到3属26种AM真菌,其中球囊霉属(Glomus)22种,无梗囊霉属(Acaulospora)3种,原囊霉属(Archaeospora)1种。地球囊霉(Glomus geosporum)和地表球囊霉(Glomus ver-siforme)是该区域盐碱土中的优势种。13种主要植物均能被AM真菌侵染,其中玉米和马蔺的侵染率最高,达100%;根际土壤中AM真菌孢子密度范围为29~182个g-1烘干土,其中稻的孢子密度最高,达182个g-1烘干土;在不同土壤类型条件下植物的菌根侵染率具有明显的差异,其规律为草甸盐土>碱化盐土>盐化草甸土>碱化草甸土;根际土壤中孢子密度以碱化草甸土最高(101个g-1烘干土),其次为碱化盐土、草甸盐土和盐化草甸土。相关分析表明,根际土壤中AM真菌孢子密度与菌根侵染率无显著相关性。     

黄土高原柠条锦鸡儿根际AM真菌生态学研究

对陕西省延安、绥德、横山和榆林4个自然生境下柠条根际AM真菌空间分布和土壤成分进行测定分析。结果表明,AM真菌泡囊定殖率及孢子密度与样地生态条件密切相关,泡囊定殖率和孢子密度在绥德最高,丛枝定殖率在榆林最高。采样深度对孢子密度有显著影响,最大孢子密度发生在10～20cm土层,而AM真菌定殖率在0～10cm或20～30cm土层有最大值。孢子密度与泡囊定殖率呈正相关,与丛枝定殖率呈负相关。孢子密度与土壤有机质、速效磷、速效钾和Cl-含量呈负相关,泡囊定殖率与土壤pH呈正相关,而与土壤湿度、速效钾和Cl-含量呈负相关。土样中AM真菌多为球囊霉属(Glomus)种类,也有少数无梗囊霉属(Acaulospora)和巨孢囊霉属(Scutellospora)种类。建议孢子密度和泡囊定殖率可作为检测土壤环境状况的指标。     

木薯根域AMF群落结构特征及多样性研究

土壤微生物是土壤—作物系统养分循环的重要驱动力,其中丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)能够促进作物对养分的吸收。木薯是我国南方重要的经济作物,是多种行业的重要原材料。为揭示不同土壤质地木薯根域土壤AMF群落结构特征,解析土壤因子对AMF类群的影响。以木薯品种华南205 (SC205)为材料,通过田间根袋培养,利用高通量测序平台进行真菌扩增子测序,分析不同处理木薯根域AMF类群组成和多样性差异。结果表明,木薯根域土壤AMF主要为球囊霉属(Glomus)、无梗囊霉属(Acaulospora)、盾巨孢囊霉属(Scutellospora)、类球囊霉属(Paraglomus)和双型囊霉属(Ambispora)。优势属为球囊霉属和无梗囊霉属。两种土质各处理AMF属水平上无显著差异,种水平分布受土壤质地及根袋的影响,粘土AMF多样性(Simpson指数)高于砂质壤土。两种土质中都发现独有种,土壤质地对木薯根域AMF群落分布有一定的影响。RDA分析表明Glomus与速效磷、速效氮、铵态氮正相关;Acaulospora与速效磷,速效氮弱负相关;Scutellospora与所有速效养分负相关;Paraglomus与所有速效养分表现出正相关;Ambispora与大部分速效养分表现出负相关。木薯根域AMF资源丰富,不同土壤质地条件下的AMF群落组成和丰度存在差异,土壤速效养分与AMF群落结构差异密切相关。该研究为进一步探索AMF在木薯上的应用提供理论参考。     

长期种植毛竹林土壤丛枝菌根真菌群落演变趋势

为揭示长期种植毛竹林土壤丛枝菌根（Arbuscular mycorrhizae, AM）真菌群落演变特征,通过磷脂脂肪酸（Phospholipid fatty acid, PLFA）和Illumina Miseq测序平台研究了AM真菌生物量及群落结构的演变趋势。结果表明,长期种植毛竹林土壤养分含量总体呈下降趋势,球囊霉素相关土壤蛋白（Glomalin-related soil protein, GRSP）含量及AM真菌生物量也显著降低（p<0.05）,其中易提取态球囊霉素相关土壤蛋白含量与有机质、速效钾、碱解氮显著正相关（p<0.05）,而AM真菌菌丝生物量（16:1ω5 PLFA）与碱解氮极显著正相关（p<0.01）。长期种植毛竹林显著降低了土壤2~0.25 mm大团聚体比例（p<0.05）,且与AM真菌菌丝生物量极显著正相关（p<0.01）。测序结果表明,毛竹林土壤AM真菌以球囊霉属（Glomus）为优势种群,其次是无梗囊霉属（Acaulospora）,长期种植毛竹后土壤球囊霉属相对丰度显著增加而无梗囊霉属显著降低（p<0.05）。非度量多维尺度转换排序（NMDS）分析显示,对照马尾松林与不同种植年限毛竹林土壤AM真菌群落显著区分（p=0.001）,土壤含水量（p=0.005）、有效磷（p=0.014）、碱解氮（p=0.001）对AM真菌群落结构变异具有重要贡献。长期种植毛竹显著降低了AM真菌生物量、球囊霉素相关土壤蛋白含量以及2~0.25 mm大团聚体比例,并改变了AM真菌群落结构,不利于土壤碳固存和维持生态系统稳定。     

土壤因子对西藏高原草地植物AM真菌的影响

于西藏高原中部地区就土壤因子对草地植物AM真菌的影响进行的研究表明：AM真菌孢子密度与菌根侵染率、菌根侵染强度无相关性；土壤质地对AM真菌孢子密度的影响明显大于土壤类型，壤土、粉砂土中AM真菌对植物根系的侵染率高于砂壤土；土壤pH与植物根围土壤孢子密度、菌根侵染率分别呈显著正相关和正相关，与菌根侵染强度则呈负相关；土壤有机质与AM真菌孢子密度呈负相关，菌根侵染效果则随土壤有机质含量的增加而提高；高磷土壤环境对AM真菌产孢和侵染均具不同程度的抑制作用，其中植物菌根侵染率随土壤有效磷含量的提高而呈显著下降；AM真菌对莎草科植物矮生嵩草、扁穗莎草根系具有良好的侵染效应。     

喀斯特不同植被恢复阶段土壤AMF组成及多样性研究

选择贵州花江、织金、花溪3个典型喀斯特地段的不同恢复阶段(乔木、灌木和草本)土壤丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)为研究对象,基于AMF孢子的形态鉴定,计算AMF孢子密度、分离频度、物种丰度、重要值、物种均匀度指数及Shannon-Wiener多样性指数,研究喀斯特不同恢复阶段土壤AMF物种组成及多样性。结果表明:3个采样地段共分离AMF菌种4目8科10属68种,其中球囊霉属(Glomus)数量最大达35种,其次是无梗囊霉属(Acaulospora)为17种,巨孢囊霉属(Gigspora)、类球囊霉属(Paraglomus)及原囊霉属(Archaeospora)各1种;不同采样地段各植被恢复阶段的优势种不同,所有样地中层状球囊霉Glomus lamellosum具有最大的相对丰度、分离频度和重要值;AMF种分类水平上,花江样地不同恢复阶段AMF丰度表现为乔木灌木草本,织金样地为灌木草本乔木,花溪样地为灌木乔木草本;不同植被恢复阶段土壤AMF均匀度指数和香农多样性指数在花江和织金多表现为乔木灌木草本,花溪样地Shannon-Wineer指数则是灌木显著高于乔木和灌木阶段。研究表明,喀斯特土壤中因异质生境条件的差异AMF菌种组成和物种多样性具有较大的差异。     

Microbial Diversity and Bioactive Substances in Disease Suppressive Composts from India

The present study aimed to investigate microbial communities in seven Indian composts and their potential for biocontrol of Fusarium oxysporum f. sp. lycopersici. In addition, identification of bioactive substances in disease suppressive composts was also attempted. Composts were chosen based on disease suppressiveness and subjected to molecular microbial analyses. Total genomic DNA from the composts was extracted and amplified with polymerase chain reaction using primers targeting the 18S rRNA and 16S rRNA genes of fungi and bacteria, respectively. Denaturing gradient gel electrophoresis (DGGE) fingerprinting and DNA sequencing were used to identify the fungal and bacterial targets. Phylogenetic analysis of the fungal 18S rRNA ITS gene sequences showed that phylum Ascomycota was dominant in all composts, while in the bacterial 16S rRNA gene sequences, the phylum Proteobacteria was dominant. Some fungi in disease suppressive composts grouped phylogenetically close to F. oxysporum. Bacterial sequences with close similarity (>95% identity) with Actinobacterium showed a strong presence only in disease suppressive composts. Disease suppressive composts formed a separate group in the cluster analysis of 18S rRNA ITS and 16S rRNA gene sequences. Gas chromatography-time of flight-mass spectrometry was performed with compost extracts to determine if bioactive substances were present in disease suppressive composts. The analysis of compost organic matter showed a negative association of disease suppressiveness with phloroglucinol, sitosterol, and monoenoic fatty acid, while cholesterol and certain organic acids were positively associated with suppressiveness.     

Phylogenetic relationships in the North African genus <Emphasis Type="Italic">Hedysarum</Emphasis> as inferred from ITS sequences of nuclear ribosomal DNA

Sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA were analysed to precise their length (637–643 bp) and resolve phylogenetic relationships among eight Mediterranean species of the genus Hedysarum (Fabaceae). The infra-specific variability levels of the ITS sequences of spontaneous population of H. coronarium proved a lack of polymorphism both in the length and in the sequences examined in this species. Hence, a consensus ITS sequence characterising each Hedysarum species has been investigated for analysis of inter-specific polymorphisms. The level of variation of ITS sequence was high enough to make the ITS1 and ITS2 a useful tool for phylogenetic reconstruction. However, ITS2 seems to be relatively more polymorphic and more informative than ITS1 regarding length or GC percent. The phylogenic relationships in the genus Hedysarum based on ITS1 and ITS2 sequences taken independently or together, are discussed in the context of current work in molecular biosystematics. Results exhibited the distinctiveness of the two H. spinosissimum subspecies (i.e. H. spinosissimum ssp. capitatum and H. spinosissimum ssp. spinosissimum). In addition, the great similarity of the ITS sequences between H. coronarium (the only cultivated species of the genus) and H. carnosum suggests the usefulness of the latter in selection programmes to improve pastoral production in semi-arid areas.     

Phylogenetic relationships among species of Citrullus and the placement of C. rehmii De Winter as determined by Internal Transcribed Spacer (ITS) sequence heterogeneity

The internal transcribed spacer regions (ITS1 and ITS2) of the 18S-25S nuclear ribosomal DNA from the four recognized species of Citrullus (C. lanatus var. lanatus (Thunb.) Matsum. & Nakai., C. lanatus var. citroides (Bailey) Mansf., C. colocynthis (L.) Schrad., C. ecirrhosus Cogn., and C. rehmii De Winter) and Acanthosicycos naudinianus (Sond.) C. Jeffrey were amplified by PCR, and direct sequenced. Within the taxa examined, the length of ITS1 varied from 216 bp to 219 bp, and ITS2 varied from 239 bp to 249 bp. The average %CG content ranged from 59 to 64% and from 62 to 66% for ITS1 and ITS2, respectively. The greater length variation observed in ITS2 was primarily attributable to the occurrence of a (CC)_n microsatellite. Cladistic (PAUP) and phenetic (MEGA) analyses resulted in highly resolutive trees. ITS sequence analysis placed the recently described C. rehmii adjacent to the cultivated watermelon and supported the validity of the species classification of this taxa.     

滨海重盐碱地人工栽植柽柳生长动态及生态效应

柽柳(Tamarix chinensis)是盐碱地土壤改良和植被构建的先锋物种,但仅靠柽柳的自然扩散难以在滨海重盐碱地形成灌木优势群落,对盐碱地的改良作用不明显,因此探索重盐碱地人工栽植柽柳的生态效应有重要意义。本研究以撂荒地为对照,对不同树龄的人工柽柳群落的个体生物量、碳储量动态、植物物种组成及其重要值和土壤特性进行分析,以评估重盐碱地栽植柽柳的生态效应。结果显示:3年生、5年生和7年生柽柳个体单株生物量逐渐增加,群落的植被碳密度分别为4.78 t(C)·hm 2、5.56 t(C)·hm 2和6.89 t(C)·hm 2,而对照撂荒地碳密度只有0.98 t(C)·hm 2;与对照地相比,栽植柽柳显著降低了土壤表层的含盐量,对照地土壤0～10 cm的平均盐分含量高达10.53 g·kg 1,而3年生、5年生和7年生0～10 cm土壤平均含盐量分别为3.35g·kg 1、1.86 g·kg 1和5.54 g·kg 1。栽植柽柳后土壤有机质和有效氮呈增高趋势,有效钾含量显著增加,7年生柽柳土壤0～5 cm和5～15 cm的有效钾含量分别比对照地高出65.59%和28.90%。随着柽柳树龄增加群落中草本植物的丰富度逐渐升高,对照地的草本物种只有8种,7年生柽柳群落达到15种;耐盐物种在群落中的重要值随着栽植的时间逐渐降低,盐地碱篷的重要值由34.8下降到0.7,以种子兼营养繁殖的植物如獐毛和苦荬菜的优势度逐渐增大。这证明,重盐碱地人工栽植柽柳可以快速构建灌木优势群落,固碳作用明显;同时栽植柽柳为生态系统提供了进展演替的动力,灌草结合的群落结构和稳定的群落环境不仅促进盐碱地土壤表层盐分含量的降低,也促进了物种多样性的增加和群落的进展演替,是提高滨海重盐碱地利用率的有效途径。     

Autochthonous halotolerant plant growth-promoting rhizobacteria promote bacoside A yield of Bacopa monnieri (L.) Nash and phytoextraction of salt-affected soil

Phytoremediation is a promising approach for reclamation of salt-affected soil. Phytoextraction is the most commonly used process, which exploits plants to absorb, immobilize, and accumulate salt in their shoots. In this study, halotolerant plant growth-promoting rhizobacteria (PGPR) were isolated from the rhizosphere of wild grasses growing naturally in salt-affected areas of Lucknow, Uttar Pradesh (India) and were tested for their efficacies of salt-tolerance and plant growth-promoting (PGP) abilities. Based on 16S rRNA sequences, the most efficient halotolerant isolates possessing PGP traits were identified as Pseudomonas plecoglossicida (KM233646), Acinetobacter calcoaceticus (KM233647), Bacillus flexus (KM233648), and Bacillus safensis (KM233652). Application of these isolates as bio-inoculants significantly (P < 0.05) increased the growth and bacoside A yield of a medicinal plant, Bacopa monnieri (L.) Nash, grown on natural salt-affected soil. The phytoremediation of salt-affected soil was evident by the substantial increase in shoot Na⁺:K⁺ ratio of bio-inoculant-treated plants. When compared to un-inoculated control plants, the soil physico-chemical properties of bio-inoculant-treated plants were improved. The shoot and root biomass (fresh and dry weights), soil enzymes, and soil nutrient parameters showed significant positive correlations with the shoot Na⁺:K⁺ ratio. Consequently, the halotolerant PGPR screened in this study could be useful for the reclamation of saline soils concomitant with improved plant growth and bacoside A yield.     

转CryIAb水稻对稻田杂草群落组成及多样性的影响

尽管基因工程技术可以增加作物产量, 但转基因作物是否对农田生态产生影响受到广泛关注。本研究通过田间定位试验, 应用群落生态学方法研究了转CryIAb基因抗虫水稻"Mfb"连续2年在传统栽培和半野生条件下对稻田杂草群落组成及多样性的影响。调查结果显示: 转CryIAb基因稻"Mfb"与非转基因稻"明恢86"田间杂草种类没有显著差异。稻田杂草的频度和密度与栽培方式有关, 半野生稻田杂草的频度和密度显著高于传统稻田, 但相同栽培条件下, 转基因稻"Mfb"与非转基因稻"明恢86"田间杂草频度和密度在整个生长期内均无显著差异。半野生稻田物种丰富度(Sr)指数明显大于传统稻田; 相同栽培条件下, 相同生长时期抗虫转基因水稻"Mfb"与其非转基因对照"明恢86"对稻田杂草群落丰富度的影响差异不显著。稻田杂草群落优势度(D)、均匀度(J)以及多样性(H)各处理、各生长时期内转基因稻与非转基因稻相比均没有显著差异。稻田杂草Shannon-Wiener多样性指数变化无明显规律, 相同栽培方式相同生长期的抗虫转基因水稻"Mfb"与其非转基因对照"明恢86"的Shannon-wiener指数差异不显著。综合上述分析, 转CryIAb基因抗虫稻对稻田杂草群落的组成及多样性没有显著影响。     

Suppression of rice blast,cabbage black leaf spot,and tomato bacterial wilt diseases by Meyerozyma guilliermondii TA-2 and the nature of protection

This study was conducted to evaluate the efficacy of yeast strain TA-2 for controlling rice blast, cabbage black leaf spot, and tomato bacterial wilt diseases. Microscopic and phylogenetic analyses based on rDNA-internal transcribed region (ITS) and rDNA-D1/D2 sequences indicated that yeast strain TA-2 is Meyerozyma guilliermondii. Pretreatment with TA-2 by soil drenching significantly reduced the severity of black leaf spot disease caused by Alternaria brassicicola and leaf blast disease caused by Magnaporthe oryzae. Symptom development of tomato bacterial wilt caused by Ralstonia solanacearum in both soil drench and needle inoculation tests was significantly reduced in TA-2-pretreated plants under soil drenching. Disease severity and R. solanacearum growth were significantly reduced in tomato plants pretreated with yeast culture, cell suspension, or culture filtrate of TA-2 under soil drenching. TA-2 does not produce antibiotics. The present study indicates that disease suppression is systemic, as the roots were treated with TA-2 and the pathogens were inoculated onto leaves or stems, thereby separating the two spatially. M. guilliermondii TA-2 could become a promising natural antimicrobial agent against rice blast, cabbage black leaf spot, and tomato bacterial wilt diseases and might be useful as an eco-friendly control measure, contributing to sustainable agriculture.     

Molecular phylogeny of Chinese vegetable mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>) based on the internal transcribed spacers (ITS) of nuclear ribosomal DNA

Sequence variation of nuclear internal transcribed spacer regions of ribosomal DNA (ITS1, 5.8S rRNA and ITS2) from Chinese vegetable mustards (AB-genome) and its putative parents Brassica rapa (the A-genome) and Brassica nigra (the B-genome) were used to investigate the molecular phylogeny and the probable evolutional pattern of this amphidiploid species that uniquely formed in China. Totally, 16 accessions of Chinese vegetable mustard those covering nearly all the diverse variations were included in this study, and together with three accessions of B. rapa and one accession of B. nigra. The results disclosed two strongly supported clades, one containing four accessions of vegetable mustard which have closer relationship with B-genome species “B.nigra” lineage and the other containing 12 accessions of B. juncea and three A-genome accessions. This classification was in disagreement with the evidence from chloroplast DNA, mitochondrial DNA, nuclear DNA restriction fragment length polymorphism (RFLP), which suggested that B. juncea was closely related to the A-genome type. For the incongruence, we speculated that the B. juncea crops derived from Chinese have evolved through different recombined events of the diploid morphutypes and evolved unidirectional concerted evolution. The traditional phenotypic classification of B. juncea was not wholly supported by ITS results, and hence the phylogenetic relationships among these subspecies need to be reconsidered on molecular level.     

Microbial Community Changes Along a Land-Use Gradient of Desert Soil Origin

Soil harbors remarkably stabilize bacterial communities at the phylum level.However,no two soils have exactly the same structure of bacterial phyla.The structure of microbial community is strongly influenced by the type of land-use through changes in soil attributes.Using high-throughput pyrosequencing and quantitative polymerase chain reaction techniques,soil microbial community structures were investigated along a land-use gradient of 100- and 27-year farmlands,a 33-year Pinus forest,a 28-year poplar forest,and a 21-year shrubland,as well as a native desert from which all cultivated systems were converted.The results revealed that the dominant phylotypes in the native soil comprised primarily of Alphaproteobacteria,Actinobacteria,Bacteroidetes,and Firmicutes,accounting for >71.4%of the total bacterial 16S rRNA sequence reads.Changes in land-use led to a significant decrease in these dominant phylotypes down to 33.4%.In contrast,the phylotypes with low abundance,such as Acidobacteria,Chloroflexi,Nitrospira,and Gammaproteobacteria,increased sharply from 4.5%-5.9%in the native soil to 20.9%-30.2%of the total 16S rRNA gene sequences in the cultivated soils except for the soil from the shrubland.These contrasting changes in the major taxa appear to be correlated with the changes in soil attributes.For instance,bacterial and archaeal amoA genes were found to be 960-and 3 800-fold more abundant in the soil from the 100-year farmland than the native soil.The changes in numerically less dominant nitrifying phylotypes are consistent with soil inorganic nitrogen dynamics.Quantification of the 16S rRNA genes demonstrated that bacteria and archaea were about two to three orders of magnitude more abundant in the cultivated soil than in the native soil.Hence,land-use type affects the soil bacterial community structure,which has profound consequences on ecosystem function.     

中国西北干旱土壤中固定二氧化碳的RuBisCO基因丰度及其多样性研究

Arid soils where water and nutrients are scarce occupy over 30% of the Earth's total surface. However, the microbial autotrophy in the harsh environments remains largely unexplored. In this study, the abundance and diversity of autotrophic bacteria were investigated, by quantifying and profiling the large subunit genes of ribulose-1,5-bisphosphate carboxylase/oxygenase(Ru Bis CO) form I(cbb L) responsible for CO2 fixation, in the arid soils under three typical plant types(Haloxylon ammodendron, Cleistogenes chinensis,and Reaumuria soongorica) in Northwest China. The bacterial communities in the soils were also characterized using the 16 S r RNA gene. Abundance of red-like autotrophic bacteria ranged from 3.94 × 105 to 1.51 × 106 copies g-1dry soil and those of green-like autotrophic bacteria ranged from 1.15 × 106 to 2.08 × 106 copies g-1dry soil. Abundance of both red- and green-like autotrophic bacteria did not significantly differ among the soils under different plant types. The autotrophic bacteria identified with the cbb L gene primer were mainly affiliated with Alphaproteobacteria, Betaproteobacteria and an uncultured bacterial group, which were not detected in the 16 S r RNA library. In addition, 25.9% and 8.1% of the 16 S r RNA genes were affiliated with Cyanobacteria in the soils under H. ammodendron and R. soongorica, respectively. However, no Cyanobacteria-affiliated cbb L genes were detected in the same soils. The results suggested that microbial autotrophic CO2 fixation might be significant in the carbon cycling of arid soils, which warrants further exploration.