不同农业措施对草莓连作土壤微生物群落特征的影响

[目的]探讨不同农业措施对草莓连作土壤微生物区系、活性、功能多样性及酶活性的影响。[方法]通过田间小区试验,利用土壤酶学方法、微生物培养方法和Biolog微生物自动分析系统,分析了土壤微生物群落特征。[结果]与不施肥相比,莓-稻水旱轮作、米糠＋日晒和石灰氮均显著提高草莓连作土壤细菌所占比例、细菌/真菌、土壤微生物总数、AWCD、土壤脱氢酶活性、Shannon指数、Simpson指数和Mcintosh指数;莓-稻水旱轮作和米糠＋日晒还能提高土壤脲酶活性。与习惯施肥相比,莓-稻水旱轮作、米糠＋日晒可显著提高草莓连作土壤AWCD、Mcintosh指数,莓-稻水旱轮作和米糠＋日晒分别显著提高土壤脲酶和脱氢酶的活性。主成分分析表明,莓-稻水旱轮作、米糠＋日晒和石灰氮条件下草莓连作土壤微生物群落碳源利用特征与习惯施肥及不施肥显著不同。[结论]莓-稻水旱轮作和米糠＋日晒是控制草莓连作土壤生物退化的有效农业措施。     

云南烟草上1种新的细菌性病害病原鉴定

 2006~2007年在云南文山州的西畴县和保山市的昌宁县发现1种由细菌侵染引起的烟草新病害。主要发生在苗期(漂浮育苗)和移栽期,症状开始为白色至暗绿色小斑点、湿腐和茎上出现褐色斑点,在KB培养基上产生荧光。根据致病性、菌体形态、培养性状、生理生化反应、Biolog测试和16S rDNA序列分析将该病原菌鉴定为铜绿假单胞菌(Pseudomonas aeruginosa)。尽管该病害曾在菲律宾发生,但在中国尚属首次报道。     

Molecular characterization ofPseudomonas syringae pv.tomato isolates from Tanzania

Bacterial speck caused byPseudomonas syringae pv.tomato is an emerging disease of tomato in Tanzania. Following reports of outbreaks of the disease in many locations in Tanzania, 56 isolates ofP. syringae pv.tomato were collected from four tomato- producing areas and characterized using pathogenicity assays on tomato, carbon source utilization by the Biolog Microplate system, polymerase chain reaction and restriction fragment length polymorphism (RFLP) analysis. All theP. syringae pv.tomato isolates produced bacterial speck symptoms on susceptible tomato (cv. ‘Tanya’) seedlings. Metabolic fingerprinting profiles revealed diversity among the isolates, forming several clusters. Some geographic differentiation was observed in principal component analysis, with isolates from Arusha region being more diverse than those from Iringa and Morogoro regions. The Biolog system was efficient in the identification of the isolates to the species level, as 53 of the 56 (94.6%) isolates ofP. syringae pv.tomato were identified asPseudomonas syringae. However, only 23 isolates out of the 56 (41.1%) were identified asPseudomonas syringae pv.tomato. The results of this work indicate the existence ofP. syringae pv.tomato isolates in Tanzania that differ significantly from those used to create the Biolog database. RFLP analysis showed that the isolates were highly conserved in theirhrpZ gene. The low level of genomic diversity within the pathogen in Tanzania shows that there is a possibility to use resistant tomato varieties as part of an effective integrated bacterial speck management plan. http://www.phytoparasitica.org posting August 8, 2008.     

Shifts in the bacterial community structure and function along a vegetation gradient in the Great Xing’an Mountains

The aim of this study was to compare soil bacterial communities in the Great Xing’an Mountains that represent three dominant vegetation types (Quercus mongolica forest, shrub mixed with herb and grassland). Soil bacterial communities were analyzed by both culture-dependent physiological profiling (Biolog) and culture-independent DNA-based approaches. The Q. mongolica forest and shrub mixed with herb had higher average well color development than the grassland, and the Q. mongolica forest and shrub mixed with herb soil bacterial communities easily utilized miscellaneous and amines/amides. The bacterial community structure was distinct across the three sites. Most of Acidobacteria, Proteobacteria and Bacteroidetes were found in grassland soil, while Firmicutes was present at a higher percentage in the Q. mongolica soil. Extracellular enzyme assays indicated that the soil ecosystem in the grassland experienced altered N and P nutrient cycling dynamics. pH, available phosphorus, potassium and nitrogen were important in shaping bacterial community structure. These results suggest that vegetation type was a strong determinant of the structure and function of bacterial communities, which may subsequently lead to significant changes in ecosystem functioning.     

盐穗木根际土壤产ACC脱氨酶细菌的筛选与鉴定

【目的】研究从新疆盐碱地的盐穗木根际土壤中筛选到产ACC脱氨酶活性较高的植物根际促生菌。为ACC脱氨酶活性菌株的植物促生作用的研究奠定基础。【方法】以新疆盐碱地的盐穗木根际土壤为样品源,ACC为唯一氮源,利用筛选培养基定向富集的方法,筛选产ACC脱氨酶活性菌株。通过扫描电镜进行形态学的观察;革兰氏染色、硝酸盐还原试验和柠檬酸盐利用等生理生化试验,用Biolog Gen III板微孔鉴定及16S rDNA序列同源性分析对分离的菌株鉴定。【结果】筛选了三株具有ACC脱氨酶活性的菌株,用扫描电镜可以清晰的观察到三株菌株均为短杆菌,革兰氏染色都为阴性,均有芽孢,硝酸盐还原试验均为阳性,都能利用柠檬酸盐。三株菌株分别为1# 、3# 和5#,三株菌株的ACC脱氨酶活性的比活力分别为0.012,0.012,0.014 U/mg;1# 和5#,3# 与5# 之间酶活力差异显著(P<0.05),1#和3#之间酶活力差异不显著(P<0.05),用Biolog Gen III板微孔和16S rDNA序列同源性分析对分离的菌株1#、3# 和5# 菌株分别鉴定为Klebsiella pneumoniae、Klebsiella pneumoniae、Klebsiella oxytoca。【结论】     

咸水灌溉棉田休耕期土壤胞外酶活性和微生物多样性研究

为探究淡水资源短缺不断加剧背景下,咸水灌溉对农田土壤胞外酶活性和微生物群落多样性的影响,以河北低平原区不同矿化度咸水灌溉棉田为研究对象,利用荧光底物-微平板法和Biolog ECO微平板法,探究了咸水灌溉棉田休耕期土壤微生物多样性特征和胞外酶活性状况。结果表明:不同矿化度咸水灌溉对多数土壤胞外酶活性和土壤微生物群落均产生了显著的影响。随着灌溉水矿化度的增加,α葡萄糖苷酶活性、纤维素二糖酶活性、磷酸酶活性及β木糖苷酶活性均呈显著下降的趋势,而N-乙酰氨基葡萄糖苷酶活性却呈现增加的趋势,β葡萄糖苷酶活性则基本不受影响。咸水灌溉改变了土壤微生物对碳源的利用能力,当灌溉水矿化度较低时,土壤盐分对微生物活性具有一定的刺激作用,能够增加微生物对不同碳源的代谢能力;但当灌溉水的矿化度大于6 g·L-1时,土壤盐分对微生物活性具有较强的抑制作用。研究表明,棉花生长季实施的咸水灌溉对休耕期土壤微生物特征以及胞外酶活性产生较大影响,休耕期土壤胞外酶活性和微生物多样性研究对于咸水灌溉土壤健康状况全面精准评价不容缺失。     

石灰与黑麦草对Cu污染土壤的修复及对微生物群落的影响

通过盆栽试验研究了Cu污染土壤中添加不同剂量石灰(质量分数分别为0.1%、0.2%和0.4%,编号SH1、SH2和SH3)对黑麦草(Secale cereale)生长及Cu吸收、土壤Cu形态转化、土壤微生物群落变化等的影响,以此评价石灰对Cu污染土壤的修复效果。试验结果表明,石灰处理后黑麦草生物量及Cu吸收量均显著增加,黑麦草地上部及根系Cu含量均显著降低;SH1、SH2和SH3处理与对照相比,土壤pH显著升高,土壤可交换态Cu含量分别显著降低了58.47%、87.51%和74.54%,而碳酸盐结合态Cu含量显著增加,分别达到对照处理的1.36、1.93、1.56倍。Biolog测试结果表明,培养72 h时,石灰处理后土壤微生物AWCD值、基质丰富度S、Shannon、Simpson和Mc Intosh指数均有不同程度增加,表现为SH2SH3SH1CK;石灰处理后土壤微生物群落的碳源利用模式发生明显变化,SH2处理可利用的碳源种类最多,碳源利用程度最高。研究表明,施用质量分数0.2%石灰并种植黑麦草对该Cu污染土壤具有较好修复效果。     

模拟氮沉降对滨海湿地土壤微生物功能多样性的影响

为全面了解大气氮沉降条件下滨海湿地土壤微生物碳源利用特点,本研究在江苏盐城滨海湿地建立模拟氮沉降实验平台,设置N1(N,0 g/(hm~2·a),对照)、N2(N,3 g/(hm~2·a),低氮)和N3(N,6 g/(hm~2·a),高氮)3个处理,采用Biolog微平板法,分析了土壤微生物功能多样性在不同氮处理下的变化规律和特点。结果表明:不同氮沉降处理间土壤微生物功能多样性差异显著,AWCD值随培养时间延长而增加;Shannon和Mc Intosh多样性指数也随施氮增加呈现升高的趋势,且不同处理间多样性指数差异显著;物种多样性和功能多样性表现出相同的变化规律。土壤微生物对6大类碳源利用强度存在差异,各处理间土壤微生物对碳水化合物类碳源利用率最高,为优势碳源;主成分分析结果显示,不同处理间土壤微生物在碳源利用上有明显的空间分异,土壤微生物功能多样性的差异主要体现在对羧酸类、酚酸类和胺类碳源的利用上,其中胺类尤为突出;此外,对不同施氮处理土壤微生物群落功能多样性与土壤理化因子进行相关分析,结果显示全氮、铵态氮、全磷会对滨海湿地土壤微生物组成和功能活性产生重要影响。     

Soil bacterial functional diversity is associated with the decline of Eucalyptus gomphocephala

This study investigates whether tree decline in Eucalyptus gomphocephala (tuart) is associated with the functional diversity of soil bacterial communities. We selected 12 sites with different stages of decline and assessed crown health [Crown density (CD), Foliage transparency (FT), Uncompacted live crown ratio (ULCR), Crown dieback ratio (CDR) and Epicormic index (EI)] and soil bacterial functional diversity based on Biolog EcoPlates™ incubation [Average well colour development (AWCD), Shannon diversity (H′), richness (S) and Shannon evenness (E)]. Crown health indices differed between sites with EI being the most robust indicator of decline in crown health followed by CDR and CD (P < 0.05). Soil bacterial indices collected at 0–10 and 20–30 cm soil depth between December (summer, dry season) and May (autumn, start of wet season) differed between sites (P < 0.05), and significant relationships between crown health indices, except ULCR, and all soil bacterial indices were observed. Principle component analysis (PCA) showed that a decrease in the utilization of carbohydrates, carboxylic acids, amino acids and amines by the soil bacterial communities correlated to sites with poor crown health, indicating some changes in physiological responses of bacterial groups with declining tree health. Using stepwise regression analyses, in the 0–10 cm soil layer in December, itaconic acid had a 46% contribution to the EI. Carboxylic acids, including itaconic acid, have a strong ability to solubilize soil minerals in calcareous soil, and these possibly increased the availability of soil mineral nutrients in the healthier sites compared to the declining sites, particularly in the dry season. In addition, lack of soil water in the declining sites limited soil bacterial diversity and was positively correlated with EI in the 0–10 cm soil layer in December. In conclusion, soil bacterial functional diversity has a strong relationship with tuart decline and the importance of soil microbes in tuart ecosystem health must be considered in the future.     

Characterization of soil microbial communities under different potato cropping systems by microbial population dynamics, substrate utilization, and fatty acid profiles

The effects of 11 different 2- and 3-yr potato crop rotations on soil microbial communities were characterized over three field seasons using several techniques. Assessments included microbial populations determined by soil dilution plate counts on various general and selective culture media, microbial activity by fluorescein diacetate (FDA) hydrolysis, single carbon source substrate utilization (SU) profiles, and fatty acid methyl ester (FAME) profiles. Potato rotation crops evaluated in research plots at Newport, ME, included barley/clover, canola, green bean, millet, soybean, sweet corn, and a continuous potato control. Soil populations of culturable bacteria and overall microbial activity tended to be highest following barley, canola, and sweet corn rotations, and lowest with continuous potato. Differences among rotations were less apparent during the potato phase of the rotations. Populations of actinomycetes and fluorescent pseudomonads tended to be greater in barley rotations than in most other rotations. SU profiles derived from BIOLOG GN2 plates indicated that certain rotations, including barley, canola, and sweet corn tended to have higher overall microbial activity, and barley and sweet corn rotations averaged higher substrate richness and diversity. Soybean and potato rotations tended to have lower substrate richness and diversity. Principal component analyses of SU data revealed differences among rotation soil communities in their utilization of individual carbon sources and substrate guilds, including carbohydrates, carboxylic acids, amines/amides, and amino acids. Analyses of soil FAME profiles demonstrated distinct differences among all the rotation soils in their relative composition of fatty acids, indicating differences in their microbial community structure. Fatty acids most responsible for differentiation among rotation soils included 16:1 ω5c, 16:1 ω7c, 18:2 ω6c, 18:1 ω9c, 12:0, and 13:0 anteiso, with 16:1 ω5c being the single greatest determinant. Overall, monounsaturated fatty acids, particularly 16:1 ω5c, were most prevalent in sweet corn rotations and polyunsaturates were highest in barley and millet rotations. Straight chain saturated fatty acids comprised the greatest proportion of fatty acids in soils under continuous potato. FAME biomarkers for microorganism groups indicated barley and millet rotations had the highest ratio of fungi to bacteria, and soybean and continuous potato had the lowest ratio. This research has demonstrated that different crop rotations have distinctive effects on soil microbial communities that are detectable using a variety of techniques. Further studies will identify more specific changes associated with particular rotations and relate these changes to potential effects on disease management, crop health, and crop productivity.