Abstract: We studied on the distribution of aboveground biomass,biological characters and nitrogen fixation characters of Nostoc commune, which commonly occurs in the terrestrial blue green alga at Xilingele grassland in Inner Mongolia.Through the determination of the amount of nitrogen fixation,we found that nitrogenase activity of Nostoc commune was different between day and night.In sunny days,in morning and evening during sunny day, it was most active for Nostoc commune to fix nitrogen was almost unable determinded.at noon time,However nitrogen still could be fixed at above 5℃ night.In rainy days of summer,nitrogen could be fixed in all day.According to the data about the distribution and biomass of Nostoc commune ,the change of nitrogenase activity and the temperature during days and nights,the seasonal treads and the number of sunny and rainy days in Inner Mongolia areas,the amount of nitrogen fixation of Nostoc commune will be 1～4kg/ha·yr.

Key words: Nostoc commune, Nitrogen cycle, Amount of nitrogen fixation

摘要： 对内蒙古锡林郭勒草原地耳进行地上生物量、生理生化特性及固氮特性的研究。结果表明,地耳在晴天、早、晚是固氮能力最强的时间,中午几乎测不到固氮活性,而夜间气温不低于 5℃时仍能固氮。夏季雨天24h均能固氮。根据地耳在不同草原的分布及生物量、固氮活性昼夜变化、季节动态和年降水天数,估算出地耳在内蒙古草原的固氮量为1～4kg/hm²·a。

关键词: 念珠藻, 氮素循环, 固氮量