Assessment of Rhizospheric Microorganisms of Transgenic Populus tomentosa with Cowpea Trypsin Inhibitor (CpTI) Gene

To have a preliminary insight into biosafety of genetically transformed hybrid triploid poplars （Populus tomentosa × P bolleana）× P. tomentosa with the cowpea trypsin inhibitor （CpTD gene, two layers of rhizospheric soil （from 0 to 20cm deep and from 20 to 40cm deep, respectively） were collected for microorganism culture, counting assay and PCR analysis to assess the potential impact of transgenic poplars on non-target microorganism population and transgene dispersal. When the same soil layer of suspension stock solution was diluted at both 1：1000 and 1：10000 rates, there were no significant differences in bacterium colony numbers between the inoculation plates of both transgenic and non-transgenic poplars. The uniform results were revealed for both soil layer suspension solutions of identical poplars at both dilution rates except for non-transgenic poplars at 1：10000 dilution rates from the same type of soil. No significant variation in morphology of both Gram-positive and Gram-negative bacteria was observed under the microscope. The potential transgene dispersal from root exudates or fallen leaves to non-target microbes was repudiated by PCR analysis, in which no CpTI gene specific DNA band was amplified for 15 sites of transgenic rhizospheric soil samples. It can be concluded that transgenic poplar with the CpTI gene has no severe impact on rhizospheric microorganisms and is tentatively safe to surrounding soil micro-ecosystem.

Influences of Oyster Shell Soil Conditioner on Soil and Plant Rhizospheric Microorganisms

Oyster shell soil conditioner had significant influence on soil and rhizospheric microorganisms in their biomass,respiratory intensity and nutritional requirement. It could stimulate growth of soil and rhizospheric microorganisms, especially nitrogen-fixers, and intensify soil respiration in proportion to the dose and fertilizing time of the conditioner, leading to the increase in the number of nitrogen fixing bacteria and the decrease in the number of bacteria with special nutrition demands.

Ecological effects of crude oil residues on the functional diversity of soil microorganisms in three weed rhizospheres

Ecological effects of crude oil residues on weed rhizospheres are still vague. The quantitative and diversity changes and metabolic responses of soil-bacterial communities in common dandelion （Taraxacum officinale）, jerusalem artichoke （Silphiurn perfoliatum L.） and evening primrose （A colypha australis L.） rhizospheric soils were thus examined using the method of carbon source utilization. The results indicated that there were various toxic effects of crude oil residues on the growth and reproduction of soil bacteria, but the weed rhizospheres could mitigate the toxic effects. Total heterotrophic counting colony-forming units （CFUs） in the rhizospheric soils were significantly higher than those in the non-rhizospheric soils. The culturable soil-bacterial CFUs in the jerusalem artichoke （S. perfoliatum） rhizosphere polluted with 0.50 kg/pot of crude oil residues were almost twice as much as those with 0.25 kg/pot and without the addition of crude oil residues. The addition of crude oil residues increased the difference in substrate evenness, substrate richness, and substrate diversity between non-rhizospheric and rhizospheric soils of T. officinale and A. australis, but there was no significant （p〉0.05） difference in the Shannon＇s diversity index between non-rhizospheric and rhizospheric soils of S. perfoliatum. The rhizospheric response of weed species to crude oil residues suggested that S. perfoliatum may be a potential weed species for the effective plant-microorganism bioremediation of contaminated soils by crude oil residues.

Effects of Combination of Straw Returning and a Microbial Agent on Microorganisms and Enzyme Activity in Rhizosphere Soil and Yield of Late Rice

By using red soil and late rice Wufengyou T025 as the tested materials,the influences of straw returning with a microbial agent on the quantity of microorganisms and enzyme activity in rhizosphere soil in fields were studied,and soil productivity was tested with yield and agricultural traits of late rice. The results showed that straw returning with the microbial agent could significantly improve the quantity of bacteria,fungi and actinomyces in soil,enhance the activity of sucrase,urease,catalase and cellulase,and improve the number of grains per spike,setting percentage,thousand seed weight and yield of late rice. The combination of rice straw returning and the microbial agent has a good prospect of application.

Diversity of Phosphate-Dissolving Microorganisms in Corn Rhizosphere

Rhizosphere and nonrhizopshere soils were sampled during corn growth. Total, inorganic phosphate-dissolving and lecithin-mineralizing bacteria, fungi and actinomyctes were determined by plate counting method. Generally, the rhizosphere soil contained around 5 to 100 times more of these bacteria and fungi than the non-rhizosphere soil. However, the actinomycetes in the rhizosphere soil were significantly lower than those in the non-rhizosphere soil. The numbers of these microorganisms didn't significantly change during corn growth in the soils. However, the proportion of the phosphate-dissolving microorganisms in the total changed markedly during corn growth. Generally there were much higher percentages of phosphate-dissolving bacteria and phosphate-dissolving fungi in the rhizosphere soil than the nonrhizosphere soil. More than 90% of the fungi in rhizosphere dissolved inorganic phosphate at the seedling period, but this proportion declined to 20% at the harvesting time. The community of phosphate-dissolving microorganisms also changed during corn growth. Bacillus was dominant in the nonrhizosphere soil. However, in the rhizosphere, Pseudomonas and Enterobacter became predominant. Penicillium and Streptomyces were the main fungi and actinomycetes capable of dissolving phosphate.

Comparisons of extraction and purification methods of soil microorganism DNA from rhizosphere soil

Microorganism DNA of rhizosphere soil from Pinus koraiensis and Pinus sylvestriformis were extracted by proteinase K based on SDS method, CTAB method, PVP （polyvinylpolypyrrolidone） method, and freezing and thawing method and the crude DNA from rhizosphere soil were purified by dialysis method, silver beads absorption method, and squeezing DNA gel method. The results of different extracting and purifying methods were compared and evaluated. Results indicated that the best method of extraction for microorganism DNA in rhizosphere soil was proteinse K based on SDS method with high salt concentration of 1.0% （w/v） NaCl, which could effectively eliminate humic acids and other impurities. The dialysis method was suitable to purify DNA from rhizosphere soil because of effectively removing brown matters and humic acids and the purified products were suited to PCR amplification. Squeezing DNA gel method was also a good purification method with the advantage of inexpensive in cost and efficient in use.

Effects of surface cracks on the rhizospheric microhabitat of Artemisia ordosica in subsidence area caused by coal mining

The effects of surface cracks caused by underground coal mining on microhabitat in the rhizosphere of Artem＆ia ordosias were studied based on field investigation and sample analysis. The results show that the amounts of microorganisms, enzyme activity and water content in soil vary with the biomass ofA. ordosias, and that the account exhibits in an order of large A. ordosias〉medium A. ordosias〉small A. ordosias. Surface cracks apparently decrease microbial quantities and enzymatic ac- tivities, and change the composition and structure of microbial community in the rhizosphere of A. ordosias. Surface cracks reduce water content and electrical conductivity, enhance the R/S （ratio of root and soil） of water content, electrical conductivity and pH value, and raise the content of Na and Pb in rhizosphere soil ofA. ordosicas, It can be concluded that the disturbance of underground coal mining on the microhabitat in the rhizosphere ofA. ordosica is obvious in the early days.

Influence of rotation system on siderophere-producing microorganism(SPM) in rhizosphere soil of southern China

Soil siderophores are important for crop growth,benefit ferric iron absorption of root,and are affected by cropping patterns.The objective of this study was to evaluate the quantity of siderophores in soil of 2 continuous crop rotation patterns over 30 years in Anren country,China.Quantity and siderophore-producing capability of microorganisms in rice-riceoilseed rape(DDY)rotation and rice-rice(DD)rontinuous cropping rhizosphere soil were tested and analyzed by chrome azurol S method.Isolated strains were used to identify siderophore-producing microorganism(SPM)by PCR amplification and DNA sequencing.Results showed that 9 siderophore-producing bacteria strains were isolated from DDY rhizosphere soil while 7 strains were identified from DD rhizosphere soil.The mean solubility index which representing siderophore-producing capability of strains was 3.05.PCR amplification results indicated that bacterial were the major SPM in soil.This research indicates that crop rotation systems could drive microorganisms to produce siderophores and enrich them in bacterial communities.

Fungi Diversity of Ginseng Rhizosphere Soil in Northeastern China

[Objective] The aim was to know the pathogenic fungi types and distribution law in ginseng rhizosphere soil.[Method] During May to Oct.in 2008 and 2009,more than 200 soil samples were collected from ginseng rhizosphere soil in Ji an City,Fusong County of Jilin Province and Huanren County of Liaoning Province.Soil dilution plate method and soil particle method were adopted to isolate and culture soil fungi,then classification and identification were carried out.[Result] 33 species of 22 fungal genera were id...

Studies on the Microbial Community in the Rhizosphere Soil of Dongxiang Wild Rice

[Objective] The aim was to study the characteristics of microbial community in the rhizosphere soil of Dongxiang wild rice（Oryza rufipogon Griff.）.[Method] The microbial biomass carbon and nitrogen was estimated by the chloroform fumigation extraction method;the microbial community composition and Nitrogen cycling microbial functional groups were investigated by the Dilution plate culture method and the most probable number methods respectively.[Result] The microbial biomass carbon and nitrogen,in rhizosphere soil of Dongxiang Wild Rice was 83.02±18.23 mg/kg soil and 16.98±2.54 mg/kg soil,which was lower than that of ordinary cultivated rice;The relationship between the number of culturable microbial groups was bacteriaactinomycetesfungi,and the Nitrogen cycling microbial physiological groups was as the following：ammonifying bacteriaaerobic azotobacteriadenitrobacteriaanaerobic azotobacterianitrobacterianitrosobacteria.[Conclusion] The microbial community in the rhizosphere soil of Dongxiang Wild Rice was different from that of the ordinary cultivated rice.

Effects of Different Land Use Patterns on Soil Microbial Quantity and Activity in Hongta District,Yuxi City

[Objective] This study aimed to investigate the effects of different land use patterns on soil ecological environment. [Method] Total three representative land use patterns （corn field, cherry tree land, wood land） were selected from Hongta District, Yuxi City, and under these three patterns, soil microbial quantity and activity were studied. [Result] Under the three land use patterns, soil microorganisms were domi- nated by bacteria; soil microbial quantity ranked as wood land＇s〉cheery tree land＇s〉 corn field＇s; and total microbial activity, catalase activity and urease activity all ranked as cherry tree land＇s〉wood land＇s〉corn field＇s. [Conclusion] Soil microbial activity and functions are related to farmland management measures, as well as land use pattern and soil nutrients.

Effects of reduced nitrogen and suitable soil moisture on wheat(Triticum aestivum L.) rhizosphere soil microbiological,biochemical properties and yield in the Huanghuai Plain,China

Soil management practices affect rhizosphere microorganisms and enzyme activities, which in turn influence soil ecosystem processes. The objective of this study was to explore the effects of different nitrogen application rates on wheat(Triticum aestivum L.) rhizosphere soil microorganisms and enzyme activities, and their temporal variations in relation to soil fertility under supplemental irrigation conditions in a fluvo-aquic region. For this, we established a split-plot experiment for two consecutive years(2014–2015 and 2015–2016) in the field with three levels of soil moisture: water deficit to no irrigation(W1), medium irrigation to(70±5)% of soil relative moisture after jointing stage(W2), and adequate irrigation to(80±5)% of soil relative moisture after jointing stage(W3);and three levels of nitrogen: 0 kg ha^–1(N1), 195 kg ha^–1(N2) and 270 kg ha^–1(N3). Results showed that irrigation and nitrogen application significantly increased rhizosphere microorganisms and enzyme activities. Soil microbiological properties showed different trends in response to N level;the highest values of bacteria, protease, catalase and phosphatase appeared in N2, while the highest levels of actinobacteria, fungi and urease were observed in N3. In addition, these items performed best under medium irrigation(W2) relative to W1 and W3;particularly the maximum microorganism(bacteria, actinobacteria and fungi) amounts appeared at W2, 5.37×10^7 and 6.35×10^7 CFUs g^–1 higher than those at W3 in 2014–2015 and 2015–2016, respectively;and these changes were similar in both growing seasons. Microbe-related parameters fluctuated over time but their seasonality did not hamper the irrigation and fertilization-induced effects. Further, the highest grain yields of 13 309.2 and 12 885.7 kg ha^–1 were both obtained at W2 N2 in 2014–2015 and 2015–2016, respectively. The selected properties, soil microorganisms and enzymes, were significantly correlated with wheat yield and proved to be valuable indicators of soil quality. These results clearly demonstrated that the combined treatment(W2 N2) significantly improved soil microbiological properties, soil fertility and wheat yield on the Huanghuai Plain, China.

Using Phospholipid FattyAcid Technique toAnalysis the Rhizosphere Specific Microbial Community of Seven Hybrid Rice Cultivars

To analyze the intrinsic relationship between rhizosphere microbial community structure and variety of rice, the microbial community structures in rhizosphere of different hybrid rice cultivars were determined with phospholipid fatty acids （PLFA） analysis. Three series of new-breeding hybrid rice cultivars in China were tested in the experiment, Ilyouming 86 （II-32A/Minghui 86）, Ilyouhang 1 （II-32A/Hang 1）, and Ilyouhang 2 （II-32A/Hang 2） with H-32A as female parent, XinyouHK02 （XinA/HK02） and YiyouHK02 （YXA/HK02） with HK02 as male parent, Chuanyou 167 （ChuanxiangA/MR167） and 44you167 （Hunan44A/MR167） with MR167 as male parent. The results showed that the microbial community in rhizosphere of the hybrid rice comprised bacteria, fungi, actinomycetes, and protozoa, according to the 40 PLFA biomarkers detected. Bacteria were more abundant than fungi and actinomycetes in rhizosphere of the hybrid rice tested. Both sulfate-reducing and methane-oxidizing bacteria were found to exist in the hybrid rice rhizosphere. It was also found that the characteristics of PLFA biomarkers had correlation with the biological traits of rice. The cluster analysis suggested that microbial community structure and activity in rhizosphere were associated with genetic background of the rice cultivar.

Integrated Biological Control of Tobacco Bacterial Wilt (<i>Ralstonia solanacearum</i>) and Its Effect on Rhizosphere Microbial Community

Biological control agents and soil amendments have been applied to control tobacco bacterial wilt, but the mechanism is not well-known. In the present study, a field experiment was performed to investigate the soil physicochemical properties, disease index (DI) and disease incidence of tobacco bacterial wilt, and rhizosphere microbial community. The results show that the control efficacy of single application of antagonistic bacteria and calcium cyanamide was 46.43% and 51.92%, respectively. While the combined control efficacy of antagonistic bacteria and calcium cyanamide was 65.79%. Besides, the combined application of antagonistic bacteria and calcium cyanamide could increase soil pH, total N alkaline N, and exchangeable Ca, which were negatively associated with the microbial diversity, soil-borne pathogenic microorganisms, and incidence of tobacco bacterial wilt. Additionally, the combination of antagonistic bacteria and calcium cyanamide can improve the proportion of some antagonistic microbial species, and these antagonistic microbial species were inversely associated with the DI of tobacco bacterial wilt. In conclusion: The integrated measure may influence soil microbial communities through enhancing soil physicochemical properties and rebuild healthy soil microbial community structure to mitigate tobacco bacterial wilt. The current study presented valuable insights into the mechanisms enhancing soil health in the integrated measure.

间作黄芪对当归根际土壤微生物的影响

目的:探讨根际土壤微生物对中药材种植模式的响应方式。方法:以间作黄芪及单作下当归根际土壤为研究对象,基于高通量测序技术,分析土壤微生物在不同季节及种植模式下群落组成及功能的差异。结果:间作下Chao1指数、ACE指数高于单作,变形菌门、放线菌门、酸杆菌门、绿弯菌门和芽单胞菌门为间作下的优势菌门,芽单胞菌门的相对丰度在间作下高于单作。11月间作下γ变形菌纲、7月间作下全噬菌纲的丰度显著高于单作。KEGG功能预测表明,在不同时间及间作下根际土壤细菌与细胞过程、环境信息处理、遗传信息处理、代谢功能下属的23类二级功能基因的相对丰度存在显著差异;参与氮循环的功能基因K00371(narH/narY/nxrB)、(K00374 narI/narV)等OTU数在间作下显著高于单作;不同门、纲在间作下的共生网络比单作下连接紧密且更复杂。结论:当归间作黄芪影响土壤细菌群落组成,增加其丰富度及功能的丰富性,影响土壤氮循环能力,促进土壤微生物间的交互作用。

外源添加L-脯氨酸对棉花黄萎病发生及其根际土壤微生物群落的影响

【目的】根系分泌物是植物与土壤微生物进行互作的信号媒介,对于植物病害发生和植株生长均具有重要调控功能。论文旨在明确棉花根系分泌物L-脯氨酸抵御棉花黄萎病发生的微生态机制,揭示L-脯氨酸介导的根际微生物与棉花黄萎病发生的互作关系,为构建生物防治土传病害的有益菌群提供新视角。【方法】通过温室盆栽试验,以外源添加不同浓度的L-脯氨酸(0、50、100、200和400 mmol·L^(-1))为试验处理,采用实时荧光定量PCR(real-time qPCR)和宏基因组测序技术分别测定不同处理的土壤中大丽轮枝菌(Verticillium dahliae)DNA拷贝数量和土壤微生物群落结构及功能,采用主成分分析比较不同处理的根际土壤微生物群落结构,利用冗余分析研究土壤养分因子与微生物群落结构的相关性,利用斯皮尔曼相关分析研究微生物群落结构功能代谢途径的相关性。【结果】与空白对照相比,低浓度(50 mmol·L^(-1))L-脯氨酸处理不能够减轻棉花黄萎病的发生,高浓度(100、200和400 mmol·L^(-1))L-脯氨酸处理的病情指数分别下降22.51%、60.23%和64.23%。qPCR结果表明,L-脯氨酸处理不能够显著降低土壤中大丽轮枝菌拷贝数量。宏基因组测序分析表明,L-脯氨酸处理后细菌多样性Shannon指数显著增加,真菌多样性Shannon指数呈下降趋势。在属水平上,L-脯氨酸处理后类诺卡氏菌属(Nocardioides)、溶杆菌属(Lysobacter)、节杆菌属(Arthrobacter)、Phycicoccus、假单胞菌属(Pseudomonas)和毛霉菌属(Mucor)的相对丰度呈上升趋势。线性判别分析表明,除浓度为100 mmol·L^(-1)的L-脯氨酸外,外源添加L-脯氨酸处理后根际土壤微生物KEGG通路的富集情况发生改变。冗余分析表明,细菌群落组成受pH、电导率、硝态氮、铵态氮和有机质显著影响,而真菌群落组成与铵态氮存在显著相关性。Spearman相关分析表明,细菌的KEGG代谢通路与pH、有机质、铵态氮含量呈负相关关系,而与电导率和硝态氮呈正相关关系;真菌的大部分KEGG代谢通路与土壤养分的相关性较差。【结论】外源添加适量L-脯氨酸通过改变土壤细菌群落结构和功能,增加有益微生物的相对丰度,从而影响棉花黄萎病的发生,但其不能够改变病原菌数量。同时,根际细菌群落组成和功能均与土壤养分存在相关性。

喀斯特石山老龄林檵木根际和非根际土壤微生物群落及酶活性的旱、雨季节变化

为了解喀斯特地区土壤生物活性的季节变化及其影响因素,该文以檵木群落老龄林阶段根际和非根际土壤微生物群落为研究对象,探讨其酶活性变化以及与环境因子的关系。结果表明:(1)雨季时,根际土壤pH值、有机质、全碳、全氮、全钾、全磷含量和碱性磷酸酶、过氧化氢酶、脲酶活性低于非根际土壤,说明根际土壤养分淋失更严重且影响相关酶活性,旱季变化相反是根际土壤为供植物健康生长所采取的养分富集策略。(2)根际和非根际土壤真菌多样性为旱季显著高于雨季,非根际土壤细菌多样性为雨季显著高于旱季,但根际土壤细菌多样性季节差异不明显;无论旱季还是雨季,根际和非根际土壤优势真菌门为子囊菌门(Ascomycota)、被孢霉门(Mortierellomycota)和担子菌门(Basidiomycota),优势细菌门为放线菌门(Actinobacteriota)、变形菌门(Proteobacteria)、酸杆菌门(Acidobacteriota);季节变化对根际和非根际土壤微生物群落结构影响差异显著。(3)不同季节下根际和非根际土壤微生物群落的主导因子不同,雨季时,根际土壤为pH、过氧化氢酶和碱性磷酸酶活性,非根际土壤为过氧化氢酶、碱性磷酸酶、纤维素酶活性和全钾含量;旱季时,根际土壤为过氧化氢酶活性和土壤含水量,非根际土壤为纤维素酶和蔗糖酶活性;土壤酶活性与碳、氮、磷、钾及土壤含水量显著相关。(4)与细菌相比,根际和非根际土壤真菌功能对季节变化的响应更敏感。综上表明,根际和非根际土壤微生物群落及酶活性在雨季和旱季时所采取的适应性策略明显不同,这为喀斯特地区植被恢复和土壤演替提供了理论参考。

苦瓜枯萎病抗病与感病品种根际土壤的微生物数量消长动态分析

以28个苦瓜品种为材料,通过苗期人工接种枯萎病鉴定其抗性强弱,结果显示,28个苦瓜品种枯萎病发病程度出现较大差异,共获得高抗材料1份、感病材料11份。苦瓜根际微生物生物数量消长动态差异分析结果表明,土壤中尖孢镰刀菌数量与苦瓜抗、感品种枯萎病发生的相关性存在差异,枯萎病的发生与土壤中尖孢镰刀菌数量呈极显著正相关。抗病品种土壤微生物数量结构优于感病品种。抗病苦瓜品种根际微生物群落的丰富度和多样性更高,其真菌的Sobs、Shannon和Chao1指数分别高出36.93%、25.89%和38.58%,细菌的Sobs、Shannon和Chao1指数分别高出13.63%、12.91%和26.52%。感病苦瓜品种土壤中的pH、铵态氮、硝态氮、速效磷和有机质含量在幼苗期均高于抗病苦瓜品种,根际微生物组成受pH、氮素、有效磷等因素的综合影响。

基于高通量测序分析拉萨大黄根部内生菌及根际土壤微生物多样性研究

以拉萨大黄根部内生菌和根际土壤微生物为研究对象,采用高通量测序技术对其测序并运用生物信息学和统计学方法进行分析,以探究拉萨大黄根部内生菌及根际土壤微生物多样性。结果表明,经过聚类注释后拉萨大黄根及根际土壤中真菌共有90个OTU(OperationalTaxonomicUnit,OTU),特有OTU分别为452个和635个;根及根际土壤中细菌共有622个OTU,特有OTU分别为982个和5618个。α多样性分析显示,与根部内生细菌相比拉萨大黄根际土壤细菌估计物种数量大,物种丰富度和均匀度高(P<0.05);拉萨大黄根际土壤真菌比根部内生真菌的物种总数更多,但根际土壤真菌和根部内生真菌的群落多样性无明显差异(P>0.05)。基于β多样性分析得到拉萨大黄根部内生菌与根际土壤微生物的菌群结构存在显著差异(P<0.05、q<0.05)。从群落组成来看,在门水平上,真菌群落中拉萨大黄根及根际土壤的优势菌门为子囊菌门(Ascomycota),细菌群落中根部内生细菌相对丰度最高的为拟杆菌门(Bacteroid-ota),相对丰度为75.44%,在根际土壤中优势门为变形菌门(Proteobacteria),相对丰度为44.36%;在属水平上,真菌群落中根部可被分类的相对丰度最高的属为青霉属(Penicillium),相对丰度为21.8%,根际土壤中可分类的相对丰度最高的为截盘多毛孢属(Truncatella),相对丰度为26.16%。细菌群落中根部可被分类出来的相对丰度最高的为JC017,相对丰度为73.44%,根际土壤中可被分类的相对丰度最高的为Ba-cillus_BD,相对丰度为6.7%。

大豆连作根际土壤微生物群落构建特征

研究连作对大豆根际土壤中细菌、真菌群落组成、构建的影响,为大豆连作障碍的生物防治和农田土壤修复提供理论支持。试验于2021-2022年在沈阳农业大学铁西区定位试验站进行,试验站土壤类型为棕壤土。以玉米-大豆轮作(对照)和大豆连作根际土壤为研究对象,利用16SrDNA、ITS高通量测序技术,结合土壤化学性质和土壤酶活性测定,分析连作对大豆土壤化学性质、酶活性以及根际微生物多样性、群落构建特征的影响。结果表明:连作下,土壤全氮、全磷、全钾等土壤化学性质指标含量下降,速效钾、pH值升高;连作显著提高土壤蔗糖酶和过氧化氢酶活性,显著降低土壤脲酶、亮氨酸氨肽酶活性和N-乙酰氨基葡萄糖苷酶活性。土壤细菌多样性指数连作处理(4.63)低于轮作处理(5.34),细菌属水平下,连作增加鞘氨醇杆菌属(Sphingobacterium)和卡氏伯克霍尔德菌属(Burkholderia,LRR:1.4%;LCR:2.4%)相对丰度;土壤真菌多样性指数连作处理低于轮作处理,真菌属水平下,连作增加病原真菌镰刀菌属(Fusarium,LCR:20.5%;LRR:13.2%)相对丰度。在群落组装过程中,大豆连作根际土壤细菌群落构建主要由确定性过程主导;玉米大豆轮作根际土壤细菌群落构建主要由随机过程主导;大豆连作根际土壤真菌群落构建和玉米大豆轮作根际土壤真菌群落构建由随机过程主导。连作引起大豆根际土壤环境因子、细菌、真菌群落组成及构建的变化,病原菌相对丰度增加,其中镰刀菌(Fusarium)相对丰度的增加可能是导致大豆连作障碍发生的重要因素。