Tripartite interactions among <Emphasis Type="Italic">Paenibacillus lentimorbus</Emphasis> NRRL B-30488, <Emphasis Type="Italic">Piriformospora indica</Emphasis> DSM 11827, and <Emphasis Type="Italic">Cicer arietinum</Emphasis> L.

Tripartite interactions among Paenibacillus lentimorbus NRRL B-30488 (B-30488), Piriformospora indica DSM 11827 (DSM 11827) and their consortia (B-30488:DSM 11827:: 1:1) with native rhizobial population in the rhizosphere of Cicer arietinum L. (Chick pea) was tested for enhancing nodulations and plant growth promotion. Number of nodules and dry weight per plant significantly enhanced (P = 0.05), which is further evident by N, P, and K uptake by plants and were found to be maximum in B-30488 treated followed by B-30488: DSM 11827 and DSM 11827, as compared with uninoculated control, in 60 days grown chickpea plants. Microbial community structure in the rhizosphere of the four treatments was assessed, using Biolog Eco and MT plates. Principal component analysis (PCA) of carbon source utilization pattern on Biolog Eco plates did not show any clustering among the four samples indicating that in case of individually DSM 11827 and B-30488 treated chickpea rhizosphere there was significant change in microbial community structure, compared with lesser changes in un-inoculated and B-30488 and DSM 11827 consortium treated chickpea rhizosphere microflora. Additional carbon sources tested using Biolog MT plates, higher activity of lignin, chitin, and cellulose utilizing microbial communities in the rhizosphere being stimulated by root exudates treated with B-30488 alone or in consortia with DSM 11827, and, in turn, should encourage beneficial symbiotic or mutualistic microorganisms that can act as plant growth promoting and biocontrol agents.     

Rhizosphere competent <Emphasis Type="Italic">Pantoea agglomerans</Emphasis> enhances maize (<Emphasis Type="Italic">Zea mays</Emphasis>) and chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L.) growth,without altering the rhizosphere functional diversity

Plant growth promoting Pantoea agglomerans NBRISRM (NBRISRM) was able to produce 60.4 μg/ml indole acetic acid and solubilize 77.5 μg/ml tri-calcium phosphate under in vitro conditions. Addition of 2% NaCl (w/v) in the media induced the IAA production and phosphate solubilization by 11% and 7%, respectively. For evaluating the plant growth promotory effect of NBRISRM inoculation a micro plot trial was conducted using maize and chickpea as host plants. The results revealed significant increase in all growth parameters tested in NBRISRM inoculated maize and chickpea plants, which were further confirmed by higher macronutrients (N, P and K) accumulation as compared to un-inoculated controls. Throughout the growing season of maize and chickpea, rhizosphere population of NBRISRM were in the range 10⁷–10⁸ CFU/g soil and competing with 10⁷–10⁹ CFU/g soil with heterogeneous bacterial population. Functional richness, diversity, and evenness were found significantly higher in maize rhizosphere as compared to chickpea, whereas NBRISRM inoculation were not able to change it, in both crops as compared to their un-inoculated control. To the best of our knowledge this is first report where we demonstrated the effect of P. agglomerans strain for improving maize and chickpea growth without altering the functional diversity.     

Analogous wheat root rhizosphere microbial successions in field and greenhouse trials in the presence of biocontrol agents Paenibacillus peoriae SP9 and Streptomyces fulvissimus FU14

Two Pythium-infested soils were used to compare the wheat root and rhizosphere soil microbial communities from plants grown in the field or in greenhouse trials and their stability in the presence of biocontrol agents. Bacteria showed the highest diversity at early stages of wheat growth in both field and greenhouse trials, while fungal diversity increased later on, at 12 weeks of the crop cycle. The microbial communities were stable in roots and rhizosphere samples across both soil types used in this study. Such stability was also observed irrespective of the cultivation system (field or greenhouse) or addition of biocontrol coatings to wheat seeds to control Pythium disease (in this study soil infected with Pythium sp. clade F was tested). In greenhouse plant roots, Archaeorhizomyces, Debaryomyces, Delftia, and unclassified Pseudeurotiaceae were significantly reduced when compared to plant roots obtained from the field trials. Some operational taxonomic units (OTUs) represented genetic determinants clearly transmitted vertically by seed endophytes (specific OTUs were found in plant roots) and the plant microbiota was enriched over time by OTUs from the rhizosphere soil. This study provided key information regarding the microbial communities associated with wheat roots and rhizosphere soils at different stages of plant growth and the role that Paenibacillus and Streptomyces strains play as biocontrol agents in supporting plant growth in infested soils.     

宁南山区典型植物根际与非根际土壤微生物功能多样性

选择宁南山区9种典型植物的根际与非根际土壤为研究对象,采用Biolog方法对土壤微生物功能多样性进行了研究。结果表明:9种不同植物根际土壤与非根际土壤的微生物活性(AWCD)、微生物多样性指数和微生物均匀度指数均存在明显差异;除冰草外,其他各种植物的根际土壤的微生物活性AWCD、微生物多样性指数和微生物均匀度指数均比非根际土壤的高;9种典型植物根际土壤微生物主要碳源利用类型是羧酸类和氨基酸类,非根际土壤微生物主要碳源利用类型是羧酸类、胺类、氨基酸类;微生物活性、微生物多样性指数和微生物均匀度指数两两之间均达到了极显著相关,与土壤化学性质各指标之间均未达到显著相关水平。     

广东省本地油茶和引种油茶根际土壤微生物群落特征

【背景】近年来,油茶低效林面积较大,根际土壤微生物影响林木抗性和生长,对林业可持续发展具有重要意义。【目的】了解广东省本地油茶和引种油茶根际土壤微生物群落特征。【方法】利用高通量测序分析油茶根际土壤微生物群落组成。【结果】油茶根际土壤细菌有26门77纲201目377科593属676种,真菌有14门50纲121目266科502属631种。油茶根际土壤中的优势细菌为酸杆菌门和变形菌门,优势真菌为子囊菌门和担子菌门。两种油茶根际土壤微生物组成差异显著,本地油茶根际土壤的细菌多样性显著高于引种油茶。在门水平上,脱硫杆菌门细菌和罗兹菌门、被孢霉门真菌的相对丰度在两种油茶间差异显著,Amorphotheca在本地油茶根际土壤中特异性富集。两种油茶根际土壤细菌碳代谢相对丰度差异显著,真菌以腐生营养型为主,其次为病理营养型和共生营养型。本地油茶根际土壤中显著富集土壤腐生菌,而共生营养型真菌(尤其是丛枝菌根真菌)相对丰度(6.43%)显著低于引种油茶中(21.83%)。此外,有机质和养分含量是影响油茶根际土壤微生物群落的关键因子。【结论】本地油茶和引种油茶根际土壤微生物群落组成和结构差异显著,Amorp...     

Plant and soil effects on bacterial communities associated with Miscanthus × giganteus rhizosphere and rhizomes

Bacterial assemblages, especially diazotroph assemblages residing in the rhizomes and the rhizosphere soil of Miscanthus × giganteus, contribute to plant growth and nitrogen use efficiency. However, the composition of these microbial communities has not been adequately explored nor have the potential ecological drivers for these communities been sufficiently studied. This knowledge is needed for understanding and potentially improving M. × giganteus – microbe interactions, and further enhancing sustainability of M. × giganteus production. In this study, cultivated M. × giganteus from four sites in Illinois, Kentucky, Nebraska, and New Jersey were collected to examine the relative influences of soil conditions and plant compartments on assembly of the M. × giganteus‐associated microbiome. Automated ribosomal intergenic spacer (ARISA) and terminal restriction fragment length polymorphism (T‐RFLP) targeting the nifH gene were applied to examine the total bacterial communities and diazotroph assemblages that reside in the rhizomes and the rhizosphere. Distinct microbial assemblages were detected in the endophytic and rhizosphere compartments. Site soil conditions had strong correlation with both total bacterial and diazotroph assemblages, but in different ways. Nitrogen treatments showed no significant effect on the composition of diazotroph assemblages in most sites. Endophytic compartments of different M. × giganteus plants tended to harbor similar microbial communities across all sites, whereas the rhizosphere soil of different plant tended to harbor diverse microbial assemblages that were distinct among sites. These observations offer insight into better understanding of the associative interactions between M. × giganteus and diazotrophs, and how this relationship is influenced by agronomic and edaphic factors.     

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.     

Studies on the microbial populations of the rhizosphere of big sagebrush (<Emphasis Type="Italic">Artemisia tridentata</Emphasis>)

Prolonged use of broad-spectrum antibiotics has led to the emergence of drug-resistant pathogens, both in medicine and in agriculture. New threats such as biological warfare have increased the need for novel and efficacious antimicrobial agents. Natural habitats not previously examined as sources of novel antibiotic-producing microorganisms still exist. One such habitat is the rhizosphere of desert shrubs. Here, we show that one desert shrub habitat, the rhizosphere of desert big sagebrush (Artemisia tridentata) is a source of actinomycetes capable of producing an extensive array of antifungal metabolites. Culturable microbial populations from both the sagebrush rhizosphere and nearby bulk soils from three different sites were enumerated and compared, using traditional plate-count techniques and antibiotic activity bioassays. There were no statistical differences between the relative numbers of culturable non-actinomycete eubacteria, actinomycetes and fungi in the rhizosphere versus bulk soils, but PCR amplification of the 16S rRNA gene sequences of the total soil DNA and denaturing gradient gel electrophoresis showed that the community structure was different between the rhizosphere and the bulk soils. A high percentage of actinomycetes produced antimicrobials; and the percentage of active producers was significantly higher among the rhizosphere isolates, as compared with the bulk soil isolates. Also, the rhizosphere strains were more active in the production of antifungal compounds than antibacterial compounds. 16S rRNA gene sequence analysis showed that sagebrush rhizospheres contained a variety of Streptomyces species possessing broad spectrum antifungal activity. Scanning electron microscopy studies of sagebrush root colonization by one of the novel sagebrush rhizosphere isolates, Streptomyces sp. strain RG, showed that it aggressively colonized young sagebrush roots, whereas another plant rhizosphere-colonizing strain, S. lydicus WYEC108, not originally isolated from sagebrush, was a poor colonizer of the roots of this plant, as were two other Streptomyces isolates from forest soil. These results support the hypothesis that the rhizosphere of desert big sagebrush is a promising source of habitat-adapted actinomycetes, producing antifungal antibiotics.     

不同生境黑果枸杞根际与非根际土壤微生物群落多样性

研究典型生境黑果枸杞根际与非根际土壤微生物群落多样性及其与土壤理化性质间的关系,为进一步研究黑果枸杞抗逆性提供理论数据。采集新疆精河县艾比湖地区(EB)盐碱地、乌苏市(WS)路旁荒地、五家渠市(WQ)人工林带的黑果枸杞根际与非根际土壤,利用Illumina-MiSeq高通量测序技术分析细菌和真菌群落组成和多样性。结果表明:根际土壤细菌多样性高于非根际土壤(WQ除外),而根际真菌多样性低于非根际土壤。WQ非根际土壤细菌和真菌多样性均高于EB和WS;根际细菌多样性排序为EBWSWQ,根际真菌多样性排序为WSEBWQ。根际土壤优势细菌门依次是变形菌门、拟杆菌门、放线菌门、酸杆菌门,真菌优势门为子囊菌门、担子菌门。根际土壤细菌变形菌门、拟杆菌门、酸杆菌门的相对丰度高于非根际土壤,而厚壁菌在根际土壤中的丰度显著降低,真菌优势门丰度在根际土和非根际土中的变化趋势因地区而异; Haliea、Gp10、Pelagibius、Microbulbifer、假单胞菌属、Thioprofundum、Deferrisoma是根际土壤细菌优势属;多孢子菌属、支顶孢属、Corollospora、Cochlonema是根际真菌优势属。细菌、真菌优势类群(门、属)的组成以及丰富度存在地区间差异,厚壁菌门在EB地区的丰富度显著高于含盐量较低的WS、WQ;盐碱生境EB中根际土壤嗜盐细菌的丰度高于非盐碱生境(WQ、WS),如盐单胞菌属、动性球菌属、Geminicoccu、Pelagibius、Gracilimonas、Salinimicrobium等。小囊菌属是EB根际真菌的最优势属,Melanoleuca是WQ和WS的最优势属,地孔菌属、Xenobotrytis、Brachyconidiellopsis、多孢子菌属等在EB根际土壤中的丰度显著高于WQ和WS。非盐碱生境(WS和WQ)的微生物群落之间的相似性较高,并且高于与盐碱环境(EB)之间的相似性,表明土壤含盐量对微生物群落组成丰度具有重要的影响。     

Spatio-temporal variation of rhizosphere soil microbial abundance and enzyme activities under different vegetation types in the coastal zone,Shandong, China

In coastal sandy soils, the establishment of a plant cover is fundamental to avoid degradation and desertification processes. A better understanding of the ability of plants to promote soil microbial process in these conditions is necessary for successful soil reclamation. The current study was to investigate the ability of four different plant species to regenerate the microbiological processes in the rhizosphere soil and to discuss which species were the most effective for the reclamation of the coastal zone. The rhizosphere soils were studied by measuring microbial abundance (bacteria, fungi, actinomycetes, and ammonifiers), enzyme activities (invertase, catalase, urease, and phosphatase) and their relationship. Microbial abundance greatly varied among rhizospheres of different plant species (p < 0.05). Phragmites australis supported the highest amount of bacterial, actinomycetes, and ammonifiers abundance, and Echinochloa crusgalli supported the highest fungi abundance. In addition, the significant differences in rhizosphere enzyme activities of different plant species were also observed. There was a significant linear correlation between rhizosphere soil microbial abundances and enzyme activities between bacteria and urease and between fungi and catalase, but no such significant relationship was found between all rhizosphere soil microbial abundance and phosphatases. It was concluded that different plant species in coastal areas have different rhizosphere soils due to the impact of the different root exudates and plant residues of the microbial properties. In addition, natural grasslands (P. australis and E. crusgalli) are the most effective for revegetating coastal sandy soils.     

独山子区优势草本植物根际与非根际土壤微生物功能多样性

以独山子区3种优势草本植物的根际与非根际土壤为研究对象,采用Biolog-ECO微平板法对土壤微生物功能多样性进行了研究。结果表明:3种不同植物根际与非根际土壤微生物代谢活性(AWCD)、丰富度指数Shannon(H)和均匀度指数Mc Intosh(U)均存在不同差异,且博乐蒿根际土壤微生物功能多样性均优于非根际土壤及其他两种植物;根际土壤微生物对糖类、脂类、酸类和胺类碳源物质比较敏感,非根际土壤微生物敏感于酸类、氨基酸类以及糖类碳源,根际土壤微生物对碳源的利用能力更强,且不同植物根际环境微生物碳源利用特征不同;微生物活性、丰富度指数和微生物均匀度指数与土壤pH值、SOM、AP和NO-3-N存在显著正相关(P0.05);博乐蒿根际土壤养分含量与微生物活性均较高,对环境的适应性更强,在独山子区生态环境管理与建设中可对其进行关注。     

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%,P0.05)、芽长(48.5%,P0.05)和根长(60%,P0.05);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。     

Effects of rhizosphere remediation and bioaugmentation on carbofuran removal from soil

Rhizosphere soil contains important sources of nutrients for microorganisms resulting in high number of microorganisms capable of degrading various types of chemicals in the soil. Thus, this study investigated a carbofuran dissipation in rhizosphere soils of 6 weeds namely, umbrella sedge (Cyperus iria L.), fuzzy flatsedge (C. pilosus V.), small flower umbrella plant (C. difformis L.), tall-fringe-rush hoorah grass (Fimbristylis miliacea V.), cover fern (Marsilea crenata P.), and water primrose (Jussiaea linifolia V.). Rhizosphere soil of fuzzy flatsedge showed the shortest half-life (t_1/2) of carbofuran (15 days) among other soils. So, it was selected to be used in the bioaugmentation experiment using carbofuran degrader namely Burkholderia cepacia, PCL3, as inoculum in order to examine whether they would improve carbofuran degradation in soil. The results showed that the addition of PCL3 into rhizosphere soil did not improve carbofuran degradation suggesting that microorganisms in rhizosphere soil might be capable enough to remove carbofuran from soil. The number of carbofuran degraders in the rhizosphere soils was greater than in bulk soil 10–100 times which might be responsible to a rapid degradation of carbofuran in rhizosphere soils without the addition of PCL3. The ability of PCL3 to degrade carbofuran was evident in bulk soil (t_1/2 of 12 days) and autoclaved soils (t_1/2 13–14 days) when compared to soils without an inoculation (t_1/2 of 58 days) indicated that the addition of a degrader was useful in improving carbofuran degradation in soil.     

Plant growth promoting potential of the fungus <Emphasis Type="Italic">Discosia</Emphasis> sp. FIHB 571 from tea rhizosphere tested on chickpea,maize and pea

The ITS region sequence of a phosphate-solubilizing fungus isolated from the rhizosphere of tea growing in Kangra valley of Himachal Pradesh showed 96% identity with Discosia sp. strain HKUCC 6626 ITS 1, 5.8S rRNA gene and ITS 2 complete sequence, and 28S rRNA gene partial sequence. The fungus exhibited the multiple plant growth promoting attributes of solubilization of inorganic phosphate substrates, production of phytase and siderophores, and biosynthesis of indole acetic acid (IAA)-like auxins. The fungal inoculum significantly increased the root length, shoot length and dry matter in the test plants of maize, pea and chickpea over the uninoculated control under the controlled environment. The plant growth promoting attributes have not been previously studied for the fungus. The fungal strain with its multiple plant growth promoting activities appears attractive towards the development of microbial inoculants.     

三种土壤条件下紫茎泽兰根际的酶活性及细菌群落状况

紫茎泽兰被列为我国危害最严重的外侵植物,为探索其侵入机制,以四川省凉山州的3种主要土壤?红壤、黄壤和紫色土为研究对象,比较了根际和非根际土壤(距离根系约20 cm)的酶活性及细菌群落。结果表明,尽管土壤类型不同,根际酶活性(过氧化氢酶、酸性磷酸酶、脲酶和蔗糖酶)及微生物量碳氮显著高于非根际,说明紫茎泽兰的根系生命活动促进根际微生物生长繁殖,数量增加,活性增强,有益于土壤养分供应,促进紫茎泽兰生长,提高生存竞争优势。在不同类型的土壤中,紫茎泽兰根际细菌的分类单元数和主成分方差比非根际降低或无显著变化,说明紫茎泽兰对土壤细菌群落的影响因土壤而异。3种土壤的优势菌株种类差异极大,根际20种优势细菌中仅链霉菌1(Streptomyces1)为共有菌株,非根际仅有绿弯菌(Chloroflexi KD4-96)为共有菌株,说明紫茎泽兰能在细菌群落不同的土壤上生长,具有极强的适应性。但是,3种土壤的优势细菌均为放线菌门、变形菌门和拟杆菌门,合计占细菌总量的60.69%—78.75%;就同一种土壤而言,根际20种优势细菌中有8—11株与非根际相同。因此,土壤类型是决定细菌群落的主要因素,但因紫茎泽兰入侵而发生一定程度的变化。     

宁夏荒漠草原蒙古冰草功能性状和根际效应对土壤性状的响应

植物功能性状组合的权衡是植物适应土壤环境的重要机制,它也通过对根际效应的调控进而影响着根际过程和生态系统功能。以位于宁夏盐池县的典型荒漠草原为研究区域,通过对灰钙土、黑垆土和风沙土中蒙古冰草功能性状和根际效应的对比分析,探究不同土壤对蒙古冰草功能性状和根际效应的影响以及它们之间的关系。结果表明：(1)不同土壤中蒙古冰草根际和非根际土壤理化性质存在显著差异,根际土壤理化性质的变化与非根际土壤性质有关。(2)不同土壤中的根际效应大小存在差异,不同因子的根际效应大小因土壤而异,总体表现为风沙土最大,灰钙土最小;土壤理化性质是影响蒙古冰草根际效应的主要因素,可解释根际效应变异的69.5%。(3)土壤理化性质与蒙古冰草功能性状密切相关,其对根长和根冠比的影响最大;蒙古冰草功能性状与根际效应大小密切相关,根长和根冠比是影响根际效应的主要因子。研究表明蒙古冰草通过根际效应改善了土壤性质,进而提高土壤质量,这种作用受土壤理化性质和植物功能性状等因子的共同影响。     

Paenibacillus lentimorbus enhances growth of chickpea (Cicer arietinum L.) in chromium-amended soil

Chromium (Cr), with its great economic importance in industrial use, is a major metal pollutant of the environment. It affects soil microbial activity and soil fertility, resulting in losses in yield of plants. Paenibacillus lentimorbus B-30488^r (B-30488^r) tolerated 200 μg ml⁻¹ of Cr under in vitro conditions and produced the plant growth promoting substance indole acetic acid in the presence of Cr. Our in vitro study indicates enhancement in B-30488^r biofilm formation by sodium alginate (SA) and calcium chloride (CaCl₂) both in absence and presence of supplemented Cr(VI) as compared to unsupplemented control. The plant growth promoting effects caused by the B-30488^r biofilm in rhizosphere of chickpea under Cr(VI) stress suggests a phytoprotective role of B-30488^r biofilm. Our study reflects the multifarious role of strain B-30488^r and presents it as a potent plant growth promoting and bioremediation agent useful in Cr-contaminated rhizosphere soil, whereby the SA and CaCl₂ induced B-30488^r biofilm on plant root acts as a shield in preventing the direct access of toxic Cr to plant tissues, thus reducing its uptake in plants.     

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。     

Phenanthrene toxicity and dissipation in rhizosphere of grassland plants (Lolium perenne L. and Trifolium pratense L.) in three spiked soils

Rhizodegradation is a technique involving plants that offers interesting potential to enhance biodegradation of persistent organic pollutants such as polycyclic aromatic hydrocarbons (PAHs). Nevertheless, the behaviour of PAHs in plant rhizosphere, including micro-organisms and the physico-chemical soil properties, still needs to be clarified. The present work proposes to study the toxicity and the dissipation of phenanthrene in three artificially contaminated soils (1 g kg^-1 DW). Experiments were carried out after 2 months of soil aging. They consisted in using different systems with two plant species (Ryegrass—Lolium perenne L. var. Prana and red clover—Trifolium pratense L. var. fourragère Caillard), three kinds of soils (a silty-clay-loam soil “La Bouzule”, a coarse sandy-loam soil “Chenevières” and a fine sandy-loam soil “Maconcourt”). Phenanthrene was quantified by HPLC in the beginning (T ₀) and the end of the experiments (30 days). Plant biomass, microbial communities including mycorrhizal fungi, Rhizobium and PAH degraders were also recorded. Generally phenanthrene contamination did not affect plant biomass. Only the red clover biomass was enhanced in Chenevières and La Bouzule polluted soils. A stimulation of Rhizobium red clover colonisation was quantified in spiked soils whereas a drastic negative phenanthrene effect on the mycorrhization of ryegrass and red clover was recorded. The number of PAH degraders was stimulated by the presence of phenanthrene in all tested soils. Both in ryegrass and red clover planted soils, the highest phenanthrene dissipation due to the rhizosphere was measured in La Bouzule soils. On the contrary, in non-planted soils, La Bouzule soils had also the lowest pollutant dissipation. Thus, in rhizospheric and non-rhizospheric soils the phenanthrene dissipation was found to depend on soil clay content.     

Soil microbial community shifts explain habitat heterogeneity in two Haloxylon species from a nutrient perspective

Haloxylon ammodendron and Haloxylon persicum (as sister taxa) are dominant shrubs in the Gurbantunggut Desert. The former grows in inter-dune lowlands while the latter in sand dunes. However, little information is available regarding the possible role of soil microorganisms in the habitat heterogeneity in the two Haloxylon species from a nutrient perspective. Rhizosphere is the interface of plant–microbe–soil interactions and fertile islands usually occur around the roots of desert shrubs. Given this, we applied quantitative real-time PCR combined with MiSeq amplicon sequencing to compare their rhizosphere effects on microbial abundance and community structures at three soil depths (0–20, 20–40, and 40–60 cm). The rhizosphere effects on microbial activity (respiration) and soil properties had also been estimated. The rhizospheres of both shrubs exerted significant positive effects on microbial activity and abundance (e.g., eukarya, bacteria, and nitrogen-fixing microbes). The rhizosphere effect of H. ammodendron on microbial activity and abundance of bacteria and nitrogen-fixing microbes was greater than that of H. persicum. However, the fertile island effect of H. ammodendron was weaker than that of H. persicum. Moreover, there existed distinct differences in microbial community structure between the two rhizosphere soils. Soil available nitrogen, especially nitrate nitrogen, was shown to be a driver of microbial community differentiation among rhizosphere and non-rhizosphere soils in the desert. In general, the rhizosphere of H. ammodendron recruited more copiotrophs (e.g., Firmicutes, Bacteroidetes, and Proteobacteria), nitrogen-fixing microbes and ammonia-oxidizing bacteria, and with stronger microbial activities. This helps it maintain a competitive advantage in relatively nutrient-rich lowlands. Haloxylon persicum relied more on fungi, actinomycetes, archaea (including ammonia-oxidizing archaea), and eukarya, with higher nutrient use efficiency, which help it adapt to the harsher dune crests. This study provides insights into the microbial mechanisms of habitat heterogeneity in two Haloxylon species in the poor desert soil.