中文摘要：

固氮微生物是土壤氮素的主要贡献者之一。利用在黑龙江海伦（寒温带）、河南封丘（暖温带）和江西鹰潭（中亚热带）设置的2种农田土壤（黑土、潮土）的置换试验，研究了不同气候、土壤和种植条件对固氮微生物多样性的影响。通过直接从土壤中提取DNA，对固氮酶基因nifH PCR扩增并进行DGGE电泳的分析方法研究了2种类型土壤在3种不同水热条件下固氮微生物群落多样性的变化特征。研究结果表明，在置换到不同气候条件下3年后，土壤类型是决定固氮微生物结构及多样性的主要影响因子，其次是短期气候条件变化的影响，最后是种植玉米的影响。土壤固氮微生物多样性、优势度与土壤C/N及碱解氮含量呈显著正相关（p〈0.01），与pH呈显著负相关；多元回归分析及典范对应分析均表明土壤碱解氮含量是影响固氮微生物多样性的决定因素。水热条件与土壤固氮微生物多样性没有线性相关关系，暖温带条件下黑土固氮微生物多样性最高，而潮土最低。种植玉米提高了土壤固氮微生物多样性。

英文摘要：

In agricultural soils, besides anthropogenic sources, diazotrophs are the main source of nitrogen. Effects of temporary climate disturbance and cropping of maize on composition and diversity of nitrogen fixing bacteria in Pachic Udic Argiboroll and Fluventic Ustochrept were examined with the technique of nifH-gene targeted polymerase chain reaction （PCR）-denaturing gradient gel electrophoresis （DGGE） approach combined with advanced statistical analysis, based on soil reciprocal transplantation experiments which were set up along a latitude gradient with distinctly different temperature and precipitation. Both cluster analysis and canonical correspondence analysis （CCA） show that soil properties could be the dominant factor to stimulate variation of diazotrophic composition, whereas temporary climate disturbances also caused a certain extent of differences. Contents of organic carbon and alkali-hydrolyzable N were found to be in significantly positive correlation with Shannon and Simpson indices while pH was in significantly negative correlation. Statistical analysis show that the content of alkali-hydrolyzable N was the determinant variable which explained the differences in diazotrophic composition among all samples （p=0.002）. Hydrothermal conditions didn’t have any linear correlation with diazotrophic biodiversity. However, Pachic Udic Argiboroll showed the highest diazotrophic biodiversity while Fluventic Ustochrept showed the lowest under warm temperate climate. In addition, maize plantation increased slightly the diversity of nitrogen-fixing bacterial in all soils, except for in Chao soil in Hailun.