中文摘要：

采用室内溶液培养方法，分别研究了接种根瘤菌处理下，两种氮源和两种氮浓度对两个大豆品种根系分泌物中有机酸的影响。结果表明，合丰25号根系分泌的有机酸种类和数量无论苗期或花期，接种或不接种根瘤菌，均表现为硝态氮处理高于酰胺态氮处理，表明合丰25号大豆更喜硝态氮，硝态氮促进了有机酸的分泌。绥农10号在酰胺态氮下的有机酸种类和数量均高于硝态氮处理，表明其更喜酰胺态氮，酰胺态氮下根瘤菌的存在增加其根系分泌物中有机酸种类和数量。可见，大豆根系分泌物中有机酸的种类和数量因品种而异，因品种对氮源的喜好而变化；根瘤菌在不同程度上增强或减弱根系有机酸的分泌作用。柠檬酸受氮素供应浓度影响很大，当氮素供应浓度较低时，大豆根系分泌物中可检测到柠檬酸，供氮浓度升高则检测不到。

英文摘要：

The organic acids were detected in soybean mot exudates in order to understand the effect of the two N formations and N concentration on mot exudates under hydroponics culture. Two cultivars, HF25 and SN10, were chosen in this study. HF25 is a susceptible genotype for mot rot, while SN10 is resistant one. Two nitrogen sources were CO （NH2）2 and Ca（NO3）2, and N levels were 2.0 × 10^-3 and 5.0 × 10^-3 mol/L. Rhizobium was inoculated in each N treatment with a comparison to the un-inoculation one. In this research, the organic acids in soybean mot exudates were detected by HPLC at seedling stage and flowering stage. The results of seedling stage showed that rhizobium had a neglect effect on the species and concentration of organic acids in HF25 mot exudates under CO（NH2）2 solution compared to noninoculation one. While the species of organic acids Jin Ca（NO3）2 solution with rhizobium became less. As for SN10, rhizobium decreased the species of organic acids in CO（NH2）2 solution, but no effect in Ca（NO3）2 solution. In flowering stage, rhizobium increased the organic acids in HF25 root exudates both in CO（NH2）2 and Ca（NO3）2 solutions. There were no significantly different in SN10 under the same conditions. The concentration of organic acids in both soybean genotypes mot exudates at flowering stage was higher than that in seedling stage. Data also showed that the citric acid in mot exudates disappeared as the concentration of Ca（NO3）2 in solution increased from 2.0 × 10^-3 to 5.0 × 10^-3 mol/L, which indicated that the citric acid exudation from mot was influenced by nitrogen concentration. It can be concluded that organic acids exudation from soybean mot was affected by N source, N concentration, rhizobium, and soybean genotype.