Effect of Colletia hystrix (Clos), a pioneer actinorhizal plant from the Chilean matorral, on the genetic and potential metabolic diversity of the soil bacterial community

Colletia hystrix are dominant shrubs in the sclerophyllous matorral, a natural ecosystem in the central valley of Chile affected by erosion, soil with low fertility and limiting nitrogen. The soil microbial communities associated to these pioneer plants have received little attention even though they may have an important role in the ability of these to colonize the nutrient-poor soils from these semi-arid ecosystems. T-RFLP profiles using 16S rDNA were used to compare the bacterial community structure from soil samples (enriched and unenriched) associated to C. hystrix and neighboring soil without plant cover (bulk soil). Additionally, the microbial communities from both habitats were compared at the metabolic profile level using the Biolog EcoPlate™ system. Our results showed that the bacterial community from samples of soil associated to these plants formed a separate cluster from samples derived from the neighboring soil. These data suggest that soil associated to C. hystrix is a different microhabitat to bulk soil. When an enrichment step was performed on the samples, the T-RFLP profiles obtained showed few T-RFs suggesting that only some species were recovered. The enriched samples exhibited a low similarity between them and are clearly separated from the unenriched samples. On the other hand, the comparison of the unenriched samples from both habitats based on sole-carbon-source utilization profiles was unable to differentiate the samples according to their habitat.     

黄瓜苗期猝倒病拮抗菌的鉴定

通过甲基脂肪酸气相色谱分析法(GC-FAME)、Biolog细菌鉴定法(借助于计算机的数值分类法)和其它试验对黄瓜苗期猝倒病具有明显防治效果的16株拮抗菌株进行分类鉴定.结果表明:黄瓜苗期猝倒病拮抗菌的优势种为Pseudomonas aeruginosa 和 Bacillus brevis,其次为Stenotrophomonas maltophilia, B. polymyxa, Pseudomonas fluorescens 和 Agrobacterium radiobacter及一些还有待进一步鉴定的种.并对GC-FAME和 Biolog的鉴定结果进行了比较:在属的水平上两种方法鉴定一致的拮抗菌株为14株,占87.5%;在种的水平上鉴定一致的拮抗菌株为7株,占42.75%.GC-FAME和 Biolog对某些细菌的鉴定提供了快速而可靠的方法,但由于目前计算机数据库尚不完备,鉴定部分细菌如B. subtilis需用其它补充方法.     

红壤区油茶根际解磷细菌的筛选、鉴定及其解磷能力

研究油茶根际解无机磷细菌的解磷能力对提高红壤丘陵区土壤磷素利用效率具有重要的指导意义.本研究从油茶根际分离筛选出97株具有解无机磷能力的菌株,采用NBRI-BPB培养基进行复筛获得5株解磷能力较强的解无机磷细菌,并测定其在NBRIP培养基中有效磷含量,采用形态特征、生理生化、Biolog系统和16SrDNA序列分析鉴定细菌种类,确定WB38为耳假单胞菌(Pseudomonas auricularis),WB39(WB75)为杓兰果胶杆菌(Pectobacterium cpripedii),WB53(WB68)为路德维希肠杆菌(Enterobacter ludwigii).研究了解磷菌株WB38在不同条件对解磷能力的影响,结果表明:不同因子对该菌株解磷能力均有显著影响,其中温度对其解磷能力影响最大;该菌株培养的最适碳源和氮源分别为葡萄糖和NH4NO3;解磷细菌WB38解磷的最佳培养条件为A2B1C1D1,即温度28℃,初始pH值6.5,接种量1％,溶氧量25 mL.     

Increased microbial activity and nitrogen mineralization coupled to changes in microbial community structure in the rhizosphere of Bt corn

The interactions between plant roots and soil microorganisms are essential for the function and stability of ecosystems, primary agricultural production and plant health. Despite the importance of soil microbes the response of these microbes to large-scale cultivation of genetically modified (GM) crops is still poorly understood. This study evaluated the potential impact of two lines of transgenic Bt maize on rhizosphere microorganisms. A time-course field experiment was conducted over a period of two years in two fields in Guadalajara (Spain) with monthly sampling from April to September. Rhizosphere soil was collected from transgenic (TG) and unmodified (WT) maize plants from each field and sampling time for the analysis of several important functional and structural soil quality parameters. Total microbial activity, as determined by H³-Thymidine and C¹⁴-Leucine incorporation, was found to be higher in the rhizospheres of the transgenic plants. Similarly, differences in potential ammonification and nitrification were observed in the second year of the study. In contrast, bacterial and fungal microbial catabolic abilities, as determined by Biolog ECO and FF plate analyses, respectively, were more influenced by sampling time than the transgenic nature of the plants. Microbial community structure was also studied by bacterial and phylum-specific PCR-DGGE and PCR cloning approaches. In general, differences were again more pronounced between sampling times, as opposed to between TG versus WT plants, although marked differences were observed within the Betaproteobacteria between plant lines. For the first time it describes the presence of Iamiaceae family in soil, specifically to TG plant rhizosphere. To summarize, the study showed that some important properties of rhizopshere microbes may be impacted by Bt maize cultivation and highlighted the fact that such potential effects need to be viewed within the context of seasonal and spatial variability.     

Tebuconazole application decreases soil microbial biomass and activity

A short-term mesocosm experiment was conducted to ascertain the impact of tebuconazole on soil microbial communities. Tebuconazole was applied to soil samples with no previous pesticide history at three rates: 5, 50 and 500 mg kg⁻¹ DW soil. Soil sampling was carried out after 0, 7, 30, 60 and 90 days of incubation to determine tebuconazole concentration and microbial properties with potential as bioindicators of soil health [i.e., basal respiration, substrate-induced respiration, microbial biomass C, enzyme activities (urease, arylsulfatase, β-glucosidase, alkaline phosphatase, dehydrogenase), nitrification rate, and functional community profiling]. Tebuconazole degradation was accurately described by a bi-exponential model (degradation half-lives varied from 9 to 263 days depending on the concentration tested). Basal respiration, substrate-induced respiration, microbial biomass C and enzyme activities were inhibited by tebuconazole. Nitrification rate was also inhibited but only during the first 30 days. Different functional community profiles were observed depending on the tebuconazole concentration used. It was concluded that tebuconazole application decreases soil microbial biomass and activity.     

利用BIOLOG鉴定系统快速鉴定菜豆萎蔫病菌的研究

 本研究利用美国Biolog公司生产的MicroStation^TM V3.5系统对我国一类危险性病害菜豆萎蔫病菌及其相关菌进行了快速鉴定研究。研究结果表明,来自不同国家和寄主的24株菜豆萎蔫病菌及其相关致病变种,23株准确鉴定至种水平,其中13株鉴定至致病变种水平,种水平的鉴定准确率为95.8%,另外1株至属水平。同时2株苜蓿萎蔫病菌和2株番茄溃疡病菌均鉴定至致病变种水平。经聚类分析研究,结果支持了对格兰氏阳性植病细菌在属、种水平的分类。本研究是首次使用该系统对格兰氏阳性植病细菌进行鉴定研究,试验证明Biolog鉴定系统用于快速鉴定菜豆萎蔫病菌是一个很有用的工具,且由于其标准化程度高、快速准确,符合我国口岸植物检疫的要求。     

外加镉处理下生物质炭对土壤微生物碳代谢功能多样性的影响

采用Biolog-Eco微平板法,通过模拟实验探究外源Cd胁迫下不同量(0%、2.5%、10%,W/W)秸秆生物质炭输入后土壤微生物在碳代谢功能方面的响应机制。平均吸光度(AWCD)值、多样性指数、碳源利用特征和主成分分析结果均表明:Cd污染条件下,生物质炭的施用提高了土壤中微生物群落碳源代谢活性及功能多样性,2.5%生物质炭处理下的提高效果尤为显著。土壤微生物Mc Intosh指数上升了70.59%,群落物种均一度发生巨大的变化;土壤微生物对羧酸类、氨基酸类碳源化合物的利用能力分别提高了10倍和5倍,其中2.5%低质量分数生物质炭提高了土壤微生物对羧酸类和糖类碳源化合物利用率,10%高质量分数生物质炭却提高了氨基酸类碳源化合物的利用率。进一步分析显示,羧酸类、其他类和聚合物类碳源化合物促使两个生物质炭处理组与单加Cd对照组在碳源利用率上存在差异。     

玉米秸秆生物炭对褐土微生物功能多样性及 细菌群落的影响

生物炭施入土壤被认为是一种有效的固碳减排措施,可增加土壤有机碳及矿质养分含量,提高土壤的持水能力及保肥能力。为探明其施入土壤后对土壤微生物活性及多样性的影响,本文在盆栽试验条件下,采用Biolog与高通量测序相结合的方法,研究了CK(不施生物炭)和施用5 g·kg~(-1)、10 g·kg~(-1)、30 g·kg~(-1)、60 g·kg~(-1)玉米秸秆生物炭对土壤微生物碳源利用能力(AWCD)、功能多样性指数以及土壤细菌的丰度和多样性的影响。结果表明,随着生物炭施用量的增加,表征土壤微生物活性的AWCD值呈下降趋势,表现为:5 g·kg~(-1)处理≈CK10 g·kg~(-1)处理30 g·kg~(-1)处理60 g·kg~(-1)处理,其中CK和5 g·kg~(-1)处理间差异不显著(P0.05),而10 g·kg~(-1)、30 g·kg~(-1)和60 g·kg~(-1)处理在整个培养期间的AWCD值显著低于CK处理(P0.05);土壤微生物群落代谢功能多样性指数(H′)、碳源利用丰富度指数(S)均随生物炭施用量的增加而呈下降趋势,但均匀度指数(E)表现出相反趋势,5g·kg~(-1)、10 g·kg~(-1)、30 g·kg~(-1)、60 g·kg~(-1)各处理的H′较CK处理分别增加0.16%、-0.88%、-3.14%、-11.09%,S分别增加-2.82%、-11.27%、-18.31%、-47.89%,E分别增加1.14%、3.00%、3.73%和13.76%。主成分分析表明,与CK处理比较,5 g·kg~(-1)处理对土壤微生物群落碳源利用方式没有显著影响(P0.05),而10 g·kg~(-1)、30 g·kg~(-1)和60g·kg~(-1)处理对土壤微生物群落碳源利用方式影响显著(P0.05)。随着生物炭施用量的增加,土壤细菌OTU数目及丰富度指数(Chao1)呈增加趋势,5 g·kg~(-1)处理与CK处理差异不显著,而10 g·kg~(-1)、30 g·kg~(-1)、60 g·kg~(-1)处理的OTU数目较CK处理分别增加1.09%、5.26%、24.42%,Chao1分别增加5.73%、10.21%、37.68%。土壤中施用生物炭后土壤细菌变形菌门(Proteobacteria)的丰度在CK处理和5 g·kg~(-1)处理间差异不显著(P0.05),而10g·kg~(-1)、30 g·kg~(-1)、60 g·kg~(-1)处理较CK处理分别增加32.3%、21.1%、16.7%,拟杆菌门(Bacteroidetes)的丰度随着生物炭施用量的增加各处理较CK处理分别减少22.1%、55.3%、66.8%、50.5%。生物炭施入土壤后降低了土壤可培养微生物的活性,减少或改变了土壤微生物碳源利用的种类,使土壤原有微生物群落组分发生改变,生物炭也影响了土壤细菌各菌群在土壤中的丰度,使其分布的均匀性降低。为了不影响微生物群落结构和功能,石灰性褐土上生物炭一次还田量不能超过5 g·kg~(-1)(干土)。     

三七收获后不同年限土壤微生物代谢多样性分析

采用Biolog技术,对云南省砚山县的盘龙、阿猛、干河3个乡镇进行了三七历年种植地的调查研究,以未种植过三七的土壤为对照,研究三七收获后1~6 a不同年限对土壤养分、土壤微生物对碳源利用以及土壤微生物多样性的影响。结果表明,反映土壤微生物活性的平均颜色变化率(AWCD)并未随年限增加呈现明显变化规律;微生物培养96 h活性旺盛。对Biolog板31种碳源吸光度值聚类分析表明,3个乡镇所取三七收获后1 a和6 a土壤微生物碳源利用均可聚为一类,其土壤微生物碳源利用特征相似,其余不同年限土壤微生物碳源利用聚类并未出现一定规律;与未种植过三七的土壤相比,三七收获后1 a、6 a土壤微生物均对碳水化合物类、聚合物类、羧酸类和酚类碳源的利用分别高出25.97%~55.59%和53.14%~65.68%;随着三七收获后年限的增加,土壤微生物对碳水化合物、氨基酸类、羧酸类碳源利用呈收获后2 a升高、4 a和5 a下降趋势。收获三七后1~6 a土壤与未种植过三七的土壤相比,氮、磷、钾及有机质含量差异均不显著。除干河乡外,阿猛乡和盘龙乡收获三七后1~6 a土壤微生物与未种植过三七的相比,Shannon-Wiener指数、丰富度指数、Simpson指数均值总体差异不明显。试验说明三七轮作至少需6 a以上时间,土壤微生物对不同碳源的优势利用可反映出三七连作障碍与土壤微生物群落结构差异有密切联系。     

模拟氮沉降对三江平原小叶章湿地土壤微生物功能多样性的影响

采用Biolog-Eco方法分析了模拟氮沉降对三江平原小叶章（Calamagrostis angustifolia）湿地土壤微生物碳源利用的影响。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。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氨基酸类碳源利用率最高,为优势碳源;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相关分析表明,全氮、铵态氮、全磷会对小叶章湿地土壤微生物组成和功能活性产生显著影响。以上结果表明增加氮沉降改变了土壤微生物功能多样性。