中文摘要：

【目的】由根系活动引起的根际微生态系统的改变,特别是病原生物数量的增加是导致作物产生连作障碍的主要因素。其中,植生性病原线虫的危害是大豆连作障碍产生的重要原因之一。由于植生性病原线虫的存在往往受到其它营养类型线虫的影响,因而从线虫群落结构进行分析,不仅可以更好地反映不同营养类型的线虫之间的相互关系,而且能全面了解土壤的健康状况。本文利用末端限制性片段长度多态性分析（T-RFLP）和实时荧光定量PCR（q PCR）等分子生物学的方法,比较短期连作和长期连作线虫群落的差异,揭示长期连作大豆土壤线虫群落的变化规律,理解线虫群落与植物健康的关系,阐明线虫群落的变化在大豆连作障碍中的作用。【方法】首先,基于16sr DNA的T-RFLP指纹图谱,分析土壤中线虫的物种丰富度和不同大小的末端限制性片段（T-RF）的相对丰度。然后,通过构建克隆文库和系统发育树,鉴定T-RF片段对应的线虫种类。最后,利用q PCR,采用绝对定量的方法确定线虫群落的大小。【结果】线虫的物种丰富度随着连作年限的增加呈逐渐降低的趋势。第1年物种丰富度最高,第3年的丰富度显著低于第1年,之后逐渐降低,9年之后保持不变。大豆根际土中共检测到16个TRF,且大多数T-RF能从克隆文库中鉴定。其中,食细菌线虫（Acrobeloides）是最为丰富的线虫种类。在连作2~3年后,植物寄生线虫相对丰度增加,而在连作后期,植物寄生线虫相对丰度减少。非度量多维尺度分析（NMDS）示,第1年线虫群落与其余年限分开,而第2和第3年聚集较近,而连作9、11和13年后聚集较近。另外,线虫群落结构与p H、土壤有机质（SOM）、速效磷（AP）、细菌数量和真菌数量相关。线虫群落总丰度呈先增后降的趋势,最高值出现在第6年。线虫的基因拷贝数与土壤NH＋4和染料木因浓度呈显著?

英文摘要：

【Objectives】Soybean yield decrease and soil sinckness in the northeast China have been attributed to continuous monoculture. Continuous soybean monoculture may provide preferential food resources for specific plant- parasitic nematodes namely cyst nematode（ Heterodera glycines）,resulting in the increase in competitive advantage of disease- causing plant- parasitic nematodes over beneficial free- living forms,with resulting economic losses. Thus, understanding dynamics of nematode communities in continuous monoculture is an important aspect of soil sickness of soybean. We used terminal restriction fragment length polymorphism（ T-RFLP） and Quantitative PCR（ q PCR） assays to estimate soil nematode community in soils taken from a long- termfield experiment with continuous soybean monoculture up to 13 years. The objective of this study was to investigate whether the dynamic processes in free- living nematodes and plant- parasitic nematodes with increasing durations of continuous soybean monoculture are linked to soil sickness.【Methods】T- RFLP assays were used to estimate structure of soil nematode community in rhizosphere soils. According to T- RFLP analysis,the species richness and relative abundances of different sizes of T- RF were determined. In order to assign phylogenetic affiliation to specific T- RF,a clone library was constructed using the p MD 19- T Vector. Phylogenetic tree was constructed using the MEGA software with the Kimura two- parameter method for distance matrix calculations and the neighbor- joining method for the tree design. Finally,quantitative PCR was used to assess nematode community sizes in rhizosphere soils.【Results】The species richness of nematode communities is decreased rapidly to the lowest value in the ninth year and then remains a constant from the ninth year to the thirteenth year. The T- RFLP analysis of nematode gene shows that the nematode communities in soybean rhizosphere soil of the northeast China are dominated by Acrobeloides. The relative abundances o