内蒙古草原典型植物对土壤微生物群落的影响

为了分析内蒙古草原不同植物物种对土壤微生物群落的影响, 采用实时荧光定量PCR (real-time PCR)以及末端限制性片段长度多态性分析(terminal restriction fragment length polymorphism, T-RFLP)等分子生物学技术, 测定了退化-恢复样地上几种典型植物的根际土壤和非根际土壤中细菌和真菌的数量及群落结构。结果表明, 不同植物物种对根际和非根际细菌及根际真菌数量均有显著影响。根际土壤中的细菌和真菌数量普遍高于非根际土壤, 尤其以真菌更为明显。对T-RFLP数据进行多响应置换过程(multi-response permutation procedures, MRPP)分析和主成分分析(principal component analysis, PCA), 结果表明, 大多数物种的根际细菌及真菌的群落结构与非根际有明显差异, 并且所有物种的真菌群落可以按根际和非根际明显分为两大类群。此外, 细菌和真菌群落结构在一定程度上存在按物种聚类的现象, 以细菌较为明显。这些结果揭示了不同植物对土壤微生物群落的影响特征, 对理解内蒙古草原地区退化及恢复过程中植被演替引起的土壤性质和功能的变化有一定的帮助。     

小麦根系分泌物对黄瓜生长及土壤真菌群落结构的影响

以黄瓜为受体,以不同化感效应(促进/抑制)小麦品种为供体,采用PCR-DGGE技术,研究了小麦根系分泌物及伴生小麦对黄瓜生长及土壤真菌群落结构的影响.结果表明： 在处理第6天和第12天,化感促进效应小麦根系分泌物分别显著提高了黄瓜幼苗株高和茎粗;在处理第18天,化感促进和抑制效应小麦根系分泌物均显著提高了黄瓜幼苗株高;在处理第6天,不同化感效应小麦根系分泌物均显著降低了黄瓜幼苗根际土壤真菌群落条带数、Shannon指数及均匀度指数,有苗对照(W)显著高于无苗对照(Wn);在处理第18天,各处理的真菌群落结构条带数、Shannon指数及均匀度指数均显著高于无苗对照(Wn).伴生化感抑制效应小麦显著降低了黄瓜根际土壤真菌群落Shannon指数和均匀度指数,说明小麦根系分泌物及伴生小麦改变了土壤真菌群落结构.DGGE图谱及其主成分分析结果表明,伴生不同化感效应小麦对土壤真菌群落结构影响较大.     

Links between plant and rhizoplane bacterial communities in grassland soils, characterized using molecular techniques

Molecular analysis of grassland rhizosphere soil has demonstrated complex and diverse bacterial communities, with resultant difficulties in detecting links between plant and bacterial communities. These studies have, however, analyzed "bulk" rhizosphere soil, rather than rhizoplane communities, which interact most closely with plants through utilization of root exudates. The aim of this study was to test the hypothesis that plant species was a major driver for bacterial rhizoplane community composition on individual plant roots. DNA extracted from individual roots was used to determine plant identity, by analysis of the plastid tRNA leucine (trnL) UAA gene intron, and plant-related bacterial communities. Bacterial communities were characterized by analysis of PCR-amplified 16S rRNA genes using two fingerprinting methods: terminal restriction fragment length polymorphisms (T-RFLP) and denaturing gradient gel electrophoresis (DGGE). Links between plant and bacterial rhizoplane communities could not be detected by visual examination of T-RFLP patterns or DGGE banding profiles. Statistical analysis of fingerprint patterns did not reveal a relationship between bacterial community composition and plant species but did demonstrate an influence of plant community composition. The data also indicated that topography and other, uncharacterized, environmental factors are important in driving bacterial community composition in grassland soils. T-RFLP had greater potential resolving power than DGGE, but findings from the two methods were not significantly different.     

Stable isotope probing analysis of the influence of liming on root exudate utilization by soil microorganisms

Rhizosphere microorganisms play an important role in soil carbon flow, through turnover of root exudates, but there is little information on which organisms are actively involved or on the influence of environmental conditions on active communities. In this study, a 13CO2 pulse labelling field experiment was performed in an upland grassland soil, followed by RNA-stable isotope probing (SIP) analysis, to determine the effect of liming on the structure of the rhizosphere microbial community metabolizing root exudates. The lower limit of detection for SIP was determined in soil samples inoculated with a range of concentrations of 13C-labelled Pseudomonas fluorescens and was found to lie between 10(5) and 10(6) cells per gram of soil. The technique was capable of detecting microbial communities actively assimilating root exudates derived from recent photo-assimilate in the field. Denaturing gradient gel electrophoresis (DGGE) profiles of bacteria, archaea and fungi derived from fractions obtained from caesium trifluoroacetate (CsTFA) density gradient ultracentrifugation indicated that active communities in limed soils were more complex than those in unlimed soils and were more active in utilization of recently exuded 13C compounds. In limed soils, the majority of the community detected by standard RNA-DGGE analysis appeared to be utilizing root exudates. In unlimed soils, DGGE profiles from 12C and 13C RNA fractions differed, suggesting that a proportion of the active community was utilizing other sources of organic carbon. These differences may reflect differences in the amount of root exudation under the different conditions.     

Links between Plant and Rhizoplane Bacterial Communities in Grassland Soils, Characterized Using Molecular Techniques

Molecular analysis of grassland rhizosphere soil has demonstrated complex and diverse bacterial communities, with resultant difficulties in detecting links between plant and bacterial communities. These studies have, however, analyzed “bulk” rhizosphere soil, rather than rhizoplane communities, which interact most closely with plants through utilization of root exudates. The aim of this study was to test the hypothesis that plant species was a major driver for bacterial rhizoplane community composition on individual plant roots. DNA extracted from individual roots was used to determine plant identity, by analysis of the plastid tRNA leucine (trnL) UAA gene intron, and plant-related bacterial communities. Bacterial communities were characterized by analysis of PCR-amplified 16S rRNA genes using two fingerprinting methods: terminal restriction fragment length polymorphisms (T-RFLP) and denaturing gradient gel electrophoresis (DGGE). Links between plant and bacterial rhizoplane communities could not be detected by visual examination of T-RFLP patterns or DGGE banding profiles. Statistical analysis of fingerprint patterns did not reveal a relationship between bacterial community composition and plant species but did demonstrate an influence of plant community composition. The data also indicated that topography and other, uncharacterized, environmental factors are important in driving bacterial community composition in grassland soils. T-RFLP had greater potential resolving power than DGGE, but findings from the two methods were not significantly different.     

Pseudomonas community structure and antagonistic potential in the rhizosphere: insights gained by combining phylogenetic and functional gene-based analyses

The Pseudomonas community structure and antagonistic potential in the rhizospheres of strawberry and oilseed rape (host plants of the fungal phytopathogen Verticillium dahliae) were assessed. The use of a new PCR-DGGE system, designed to target Pseudomonas-specific gacA gene fragments in environmental DNA, circumvented common biases of 16S rRNA gene-based DGGE analyses and proved to be a reliable tool to unravel the diversity of uncultured Pseudomonas in bulk and rhizosphere soils. Pseudomonas-specific gacA fingerprints of total-community (TC) rhizosphere DNA were surprisingly diverse, plant-specific and differed markedly from those of the corresponding bulk soils. By combining multiple culture-dependent and independent surveys, a group of Pseudomonas isolates antagonistic towards V. dahliae was shown to be genotypically conserved, to carry the phlD biosynthetic locus (involved in the biosynthesis of 2,4-diacetylphloroglucinol - 2,4-DAPG), and to correspond to a dominant and highly frequent Pseudomonas population in the rhizosphere of field-grown strawberries planted at three sites in Germany which have different land use histories. This population belongs to the Pseudomonas fluorescens phylogenetic lineage and showed closest relatedness to P. fluorescens strain F113 (97% gacA gene sequence identity in 492-bp sequences), a biocontrol agent and 2,4-DAPG producer. Partial gacA gene sequences derived from isolates, clones of the strawberry rhizosphere and DGGE bands retrieved in this study represent previously undescribed Pseudomonas gacA gene clusters as revealed by phylogenetic analysis.     

AM真菌对青枯菌和根际细菌群落结构的影响

利用传统的平板培养与DGGE相结合的技术手段,研究了接种AM真菌对番茄根际土壤中的青枯菌和细菌群落结构的影响。结果表明,菌根根际土壤中的细菌总量和总DNA量都高于非菌根根际土壤,其中前者的青枯菌种群数量比后者低60倍;DGGE图谱也证实了AM真菌对青枯菌的抑制效应,还揭示出接种AM真菌对根际土壤中细菌群落结构所产生的复杂的影响。文章对AM真菌抑制青枯菌的机制进行了探讨。     

Cultivation-independent analysis of Pseudomonas species in soil and in the rhizosphere of field-grown Verticillium dahliae host plants

Despite their importance for rhizosphere functioning, rhizobacterial Pseudomonas spp. have been mainly studied in a cultivation-based manner. In this study a cultivation-independent method was used to determine to what extent the factors plant species, sampling site and year-to-year variation influence Pseudomonas community structure in bulk soil and in the rhizosphere of two Verticillium dahliae host plants, oilseed rape and strawberry. Community DNA was extracted from bulk and rhizosphere soil samples of flowering plants collected at three different sites in Germany in two consecutive years. Pseudomonas community structure and diversity were assessed using a polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) system to fingerprint Pseudomonas-specific 16S rRNA gene fragments amplified from community DNA. Dominant and differentiating DGGE bands were excised from the gels, cloned and sequenced. The factors sampling site, plant species and year-to-year variation were shown to significantly influence the community structure of Pseudomonas in rhizosphere soils. The composition of Pseudomonas 16S rRNA gene fragments in the rhizosphere differed from that in the adjacent bulk soil and the rhizosphere effect tended to be plant-specific. The clone sequences of most dominant bands analysed belonged to the Pseudomonas fluorescens lineage and showed closest similarity to culturable Pseudomonas known for displaying antifungal properties. This report provides a better understanding of how different factors drive Pseudomonas community structure and diversity in bulk and rhizosphere soils.     

甘肃省中部沿黄灌区轮作和连作马铃薯根际土壤真菌群落的结构性差异评估

甘肃省中部沿黄灌区是西北地区乃至全国重要的加工型马铃薯生产基地,然而因集约化种植带来的连作障碍问题已经严重影响到当地马铃薯种植业的可持续发展。采用大田试验与PCR-DGGE(Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis)技术相结合的方法,并通过真菌的18S r DNA序列分析,评估轮作(未连作)和连作条件下马铃薯根际土壤真菌群落在组成结构上的差异,以期为甘肃省中部沿黄灌区马铃薯连作的土壤障碍机理研究提供新证据。结果表明,同轮作相比,连作显著降低了马铃薯块茎产量和植株生物量,并且随着连作年限的延长,连作障碍也愈加严重。长期连作(6a)也导致马铃薯根冠比显著增加和植株收获指数的显著下降。在根际土壤真菌的种群数量和多样性上,连作和轮作间无显著差异,但在群落组成结构上差异明显。真菌18S r DNA测序分析进一步表明,马铃薯连作较轮作相比增加了Fusarium sp.和Fusarium solani以及Verticillium dahliae的种群或个体数量,而这些真菌是导致马铃薯土传病害的主要致病菌类型。根际土壤真菌群落组成结构的改变特别是与土传病害有关的致病菌滋生可能是导致当地马铃薯连作障碍的重要原因。     

Dynamics of fungal communities in bulk and maize rhizosphere soil in the tropics

The fungal population dynamics in soil and in the rhizospheres of two maize cultivars grown in tropical soils were studied by a cultivation-independent analysis of directly extracted DNA to provide baseline data. Soil and rhizosphere samples were taken from six plots 20, 40, and 90 days after planting in two consecutive years. A 1.65-kb fragment of the 18S ribosomal DNA (rDNA) amplified from the total community DNA was analyzed by denaturing gradient gel electrophoresis (DGGE) and by cloning and sequencing. A rhizosphere effect was observed for fungal populations at all stages of plant development. In addition, pronounced changes in the composition of fungal communities during plant growth development were found by DGGE. Similar types of fingerprints were observed in two consecutive growth periods. No major differences were detected in the fungal patterns of the two cultivars. Direct cloning of 18S rDNA fragments amplified from soil or rhizosphere DNA resulted in 75 clones matching 12 dominant DGGE bands. The clones were characterized by their HinfI restriction patterns, and 39 different clones representing each group of restriction patterns were sequenced. The cloning and sequencing approach provided information on the phylogeny of dominant amplifiable fungal populations and allowed us to determine a number of fungal phylotypes that contribute to each of the dominant DGGE bands. Based on the sequence similarity of the 18S rDNA fragment with existing fungal isolates in the database, it was shown that the rhizospheres of young maize plants seemed to select the Ascomycetes order Pleosporales, while different members of the Ascomycetes and basidiomycetic yeast were detected in the rhizospheres of senescent maize plants.     

Resilience of the rhizosphere Pseudomonas and ammonia-oxidizing bacterial populations during phytoextraction of heavy metal polluted soil with poplar

We assessed the effects of phytoextraction on the dynamics of Pseudomonas spp. and ammonia-oxidizing bacterial populations in a heavy metal (HM) polluted soil. Hybrid poplars were grown in two-compartment root containers with a medium history (> 4 years) of HM pollution for 13 weeks. Bulk and poplar rhizosphere soils were analysed by denaturing gradient gel electrophoresis (DGGE) of Pseudomonas (sensu stricto) 16S rRNA and amoA gene fragments. DGGE patterns revealed that Pseudomonas and amoA-containing populations in the contaminated soils were markedly different from those in the uncontaminated soils. Pseudomonas and amoA profiles appeared to be stable over time in the bulk soils. In contrast, contaminated rhizosphere soils revealed a clear shift of populations with removal of HM becoming similar or at least shifted to the populations of the uncontaminated soils. The effect of phytoextraction was, however, not evident in the bulk samples, which still contained large amounts of HM. Cloning and sequencing of dominant DGGE bands revealed that Pseudomonas were phylogenetically related to the Pseudomonas fluorescens cluster and the amoA sequences to Nitrosospira spp. At the last sampling, major prominent band sequences from contaminated rhizosphere soils were identical to sequences obtained from uncontaminated rhizosphere soils, indicating that the populations were dominated by the same phylotypes. This study suggests that two taxonomically different populations are able to recover after the relief of HM stress by phytoextraction practices, whereas bulk microbial activities still remained depressed.     

Dynamics of Fungal Communities in Bulk and Maize Rhizosphere Soil in the Tropics

The fungal population dynamics in soil and in the rhizospheres of two maize cultivars grown in tropical soils were studied by a cultivation-independent analysis of directly extracted DNA to provide baseline data. Soil and rhizosphere samples were taken from six plots 20, 40, and 90 days after planting in two consecutive years. A 1.65-kb fragment of the 18S ribosomal DNA (rDNA) amplified from the total community DNA was analyzed by denaturing gradient gel electrophoresis (DGGE) and by cloning and sequencing. A rhizosphere effect was observed for fungal populations at all stages of plant development. In addition, pronounced changes in the composition of fungal communities during plant growth development were found by DGGE. Similar types of fingerprints were observed in two consecutive growth periods. No major differences were detected in the fungal patterns of the two cultivars. Direct cloning of 18S rDNA fragments amplified from soil or rhizosphere DNA resulted in 75 clones matching 12 dominant DGGE bands. The clones were characterized by their HinfI restriction patterns, and 39 different clones representing each group of restriction patterns were sequenced. The cloning and sequencing approach provided information on the phylogeny of dominant amplifiable fungal populations and allowed us to determine a number of fungal phylotypes that contribute to each of the dominant DGGE bands. Based on the sequence similarity of the 18S rDNA fragment with existing fungal isolates in the database, it was shown that the rhizospheres of young maize plants seemed to select the Ascomycetes order Pleosporales, while different members of the Ascomycetes and basidiomycetic yeast were detected in the rhizospheres of senescent maize plants.     

The Effect of Biocontrol Bacteria on Rhizosphere Bacterial Communities Analyzed by Plating and PCR-DGGE

Bacillus subtilis B579, which was isolated from rhizosphere of cucumber, exhibited an excellent biocontrol activity on soil-born pathogens under greenhouse conditions. It could colonize in rhizosphere of cucumber with large number of populations after inoculated in plant growth season. To reveal the effect of high level colonization of B. subtilis B579 on rhizobacteria community structure, cultivation-based analysis coupled with denaturing gradient gel electrophoresis (DGGE) analysis were used to profile the changes of rhizobacteria community structure sampling at 1 week interval. Cultivation-based and DGGE fingerprinting analysis showed significant plant-dependent and seasonal shifts in rhizobacteria populations. Only minimal and transient effects were observed at 4–9 weeks after sowing in samples of B579 treatment, without the pathogen inoculation and showed the best plant growth potential. Sequencing of dominant bands excised from the gel revealed that Streptomyces sp. was the dominate species in soils before and after sowing. Burkholderia sp. was the dominate species in bulk soil, while Bacillus sp. was dominated in rhizosphere within the growth season. Arthrobacter ramosus and Nocardioides sp. were identified as the specific species in samples treated by B579 at the maturity and flowering stages of cucumber.     

Effect of monoculture soybean on soil microbial community in the Northeast China

Monoculture (MC) soybean, a common practice in the Northeast China, causes significant declines in soybean yield and quality. The objective of this study was to evaluate the responses of the soil microbial community and soybean yield to different soybean cropping systems. Three cropping systems were compared, (1) corn-soybean rotation (corn-corn-soybean, CS), (2) MC soybean for 3 years (S3), (3) MC soybean for 9 years (S9). Both bulk and rhizosphere soil samples were collected at three growth stages: two trifoliate (V2), full bloom (R2), and full seed (R6), respectively. Soil microbial DNA was analyzed using polymerase chain reaction (PCR)—denaturing gradient gel electrophoresis (DGGE) to assess changes in composition of bacterial and fungal communities. Prominent DGGE bands were excised and sequenced to gain insight into the identities of the predominant microbial populations. Some prominent differences were observed in bacterial DGGE patterns of amplified 16S rDNA (V3 region) among rhizosphere soils. These major differences included one DGGE band (showing 100% similarity to Arthrobacter sp.) that was enriched at R2 stages in CS and S9, and another band with 97% sequence similarity to an uncultured actinobacterium was detected at R6 stage in CS, and at R2 and R6 stages in S9. The bacterial community from bulk soil showed no significant band change in DGGE patterns among different cropping systems. In fungal DGGE patterns of the amplified 18S rDNA partial fragment, one specific band (showing 98% similarity to Trichoderma viride) occurred in rhizosphere soil of treatment CS at V2 and R6 stages and treatment S9 at R6 stage. None of the above bands were detected in treatment S3. The soybean yields and plant heights from CS and S9 were greater than those from S3. Moreover, catalase activities from CS and S9 at V2 and R2 stages were higher than those tested from S3 at the corresponding times in rhizosphere soil. The present results showed that DGGE patterns were not able to detect significant differences in diversity or evenness among microbial communities, but significant differences were found in the composition of bacterial and fungal community structures. Some distinguished bands from bacterial and fungal DGGE patterns were only enriched in CS and S9 soil, which could potentially play an important role in soybean growth development.     

Impact of biocontrol agents Pseudomonas fluorescens CHA0 and its genetically modified derivatives on the diversity of culturable fungi in the rhizosphere of mungbean

AIMS: To assess whether Pseudomonas fluorescens strain CHA0 and its genetically modified derivatives, CHA0/pME3424 (antibiotic over-producer) and CHA89 (antibiotic-deficient) could have an impact on the fungal community structure and composition in the rhizosphere of mungbean. METHODS AND RESULTS: Under glasshouse conditions, mungbean was grown repeatedly in the same soil, which was inoculated with CHA0, CHA0/pME3424, CHA89 or was left untreated. Treatments were applied to soil at the start of each 36-day mungbean growth cycle, and their effects on the diversity of the rhizosphere populations of culturable fungi were assessed at the end of the first, second and third cycles. The effects of CHA0 and CHA0/pME3424 did differ from the controls while CHA89 did not. Whereas all major fungal species were frequently isolated from both bacterized and nonbacterized rhizospheres, certain fungal species were exclusively promoted or specifically suppressed from Pseudomonas-treated soils. In general, fungal diversity and equitability tended to decrease with time while species richness slightly increased. Whilst a total of 29 fungal species were isolated from the mungbean rhizosphere, only eight species colonized the root tissues. CONCLUSIONS: Soil inoculation with Ps. fluorescens CHA0 or CHA0/pME3424 altered fungal community structure in mungbean rhizosphere but strain CHA89 failed to produce such effect. SIGNIFICANCE AND IMPACT OF THE STUDY: Pseudomonas fluorescens-mediated alteration in the composition and structure of fungal communities might have acute or lasting effects on ecosystem functioning. Furthermore, the study provides useful data pertinent to characterization of the fate of genetically modified inoculants (e.g. antibiotic-overproducing Pseudomonas strains) released into the environment.     

连作对白肋烟根际土壤细菌群落多样性的影响

以种植白肋烟1年、2年和4年的土壤为研究对象,采用末端限制性片段长度多态性(T-RFLP)技术分析根际土壤细菌群落的动态变化.结果表明:白肋烟根际土壤细菌群落香农指数和丰富度指数随着种植年限的增加呈现出先增后减的趋势,连作4年后细菌群落的多样性水平显著降低,细菌群落结构较单一.随着种植年限的增加,根际土壤细菌群落与对照的相似性指数逐渐降低.种植年限为1年、2年的土壤和对照土壤中放线菌门放线菌纲是优势类群,种植年限为4年的土壤中放线菌纲所占的比例下降,而厚壁菌门的芽孢杆菌纲成为优势类群.白肋烟连作使根际鞘氨醇单胞菌属和链霉菌属等益生菌数量减少、蜡状芽孢杆菌等潜在致病菌增加,破坏了烟草根际土壤微生物群落的平衡,使其微生态环境恶化.     

Effects of site and plant species on rhizosphere community structure as revealed by molecular analysis of microbial guilds

The bacterial and fungal rhizosphere communities of strawberry (Fragaria ananassa Duch.) and oilseed rape (Brassica napus L.) were analysed using molecular fingerprints. We aimed to determine to what extent the structure of different microbial groups in the rhizosphere is influenced by plant species and sampling site. Total community DNA was extracted from bulk and rhizosphere soil taken from three sites in Germany in two consecutive years. Bacterial, fungal and group-specific (Alphaproteobacteria, Betaproteobacteria and Actinobacteria) primers were used to PCR-amplify 16S rRNA and 18S rRNA gene fragments from community DNA prior to denaturing gradient gel electrophoresis (DGGE) analysis. Bacterial fingerprints of soil DNA revealed a high number of equally abundant faint bands, while rhizosphere fingerprints displayed a higher proportion of dominant bands and reduced richness, suggesting selection of bacterial populations in this environment. Plant specificity was detected in the rhizosphere by bacterial and group-specific DGGE profiles. Different bulk soil community fingerprints were revealed for each sampling site. The plant species was a determinant factor in shaping similar actinobacterial communities in the strawberry rhizosphere from different sites in both years. Higher heterogeneity of DGGE profiles within soil and rhizosphere replicates was observed for the fungi. Plant-specific composition of fungal communities in the rhizosphere could also be detected, but not in all cases. Cloning and sequencing of 16S rRNA gene fragments obtained from dominant DGGE bands detected in the bacterial profiles of the Rostock site revealed that Streptomyces sp. and Rhizobium sp. were among the dominant ribotypes in the strawberry rhizosphere, while sequences from Arthrobacter sp. corresponded to dominant bands from oilseed rape bacterial fingerprints.     

Pseudomonas fluorescens DR54 Reduces Sclerotia Formation,Biomass Development,and Disease Incidence of Rhizoctonia solani Causing Damping-Off in Sugar Beet

Effects of the biocontrol strain, Pseudomonas fluorescens DR54, on growth and disease development by Rhizoctonia solani causing damping-off in sugar beet were studied in soil microcosms and in pot experiments with natural, clay-type soil. In pot experiments with P. fluorescens DR54-treated seeds, significantly fewer Rhizoctonia-challenged seedlings showed damping-off symptoms than when not inoculated with the biocontrol agent. In the rhizosphere of P. fluorescens DR54 inoculated seeds, the bacterial inoculant was present in high numbers as shown by dilution plating and immunoblotting. By the ELISA antibody technique and direct microscopy of the fungal pathogen grown in soil microcosms, it was shown that the presence of P. fluorescens DR54 on the inoculated seeds had a strong inhibitory effect on development of both mycelium biomass and sclerotia formation by R. solani. In the field experiment, plant emergence was increased by treatment with P. fluorescens DR54 and the inoculant was found to be the dominating rhizosphere colonizing pseudomonad immediately after seedling emergence.     

Soil parent material is a key determinant of the bacterial community structure in arable soils

The bacterial community composition in soil and rhizosphere taken from arable field sites, differing in soil parent material and soil texture, was analyzed using terminal restriction fragment length polymorphism (T-RFLP) of 16S rRNA genes. Nine sandy to silty soils from North-East Germany could clearly be distinguished from each other, with a relatively low heterogeneity in the community structure within the field replicates. There was a relationship between the soil parent material, i.e. different glacial and aeolian sediments, and the clustering of the profiles from different sites. A site-specific grouping of T-RFLP profiles was also found for the rhizosphere samples of the same field sites that were planted with potatoes. The branching of the rhizosphere profiles corresponded partly with the soil parent material, whereas the effect of the plant genotype was negligible. Selected terminal restriction fragments differing in their relative abundance within the nine soils were analyzed based on the cloning of the 16S rRNA genes of one soil sample. A high phylogenetic diversity observed to include Acidobacteria, Betaproteobacteria, Bacteroidetes, Verrucomicrobia, and Gemmatimonadetes. The assignment of three out of the seven selected terminal restriction fragments to members of Acidobacteria suggested that this group seems to participate frequently in the shifting of community structures that result from soil property changes.