白洋淀湖滨湿地岸边带氨氧化古菌与氨氧化细菌的分布特性

Abundance and biodiversity of ammonia-oxidizing archaea and bacteria in littoral wetland of Baiyangdian Lake,North China

通过分子生物学分析方法,以amoA基因为标记,考察了氨氧化古菌(Ammonia-Oxidizing Archaea,AOA)和氨氧化细菌(Ammonia-Oxidizing Bacteria,AOB)在华北平原的白洋淀这一典型湖泊的湖滨湿地岸边带系统中的生物多样性和丰度分布。在前人的研究中,氨氧化古菌在海洋、原生态土壤和人为干扰土壤等环境中主导氨氧化过程的完成。但本研究发现,在湿地岸边带系统中氨氧化过程并不是完全由氨氧化古菌主导完成,即氨氧化古菌和氨氧化细菌在不同区域分别占据主导地位。根据主导微生物的不同,可以将湿地岸边带区域划分为陆相区、中间区和湖相区。在湿地岸边带陆相区,氨氧化古菌主导氨氧化过程,氨氧化古菌的amoA基因丰度是氨氧化细菌的526倍(AOA:1.23×108个/g干土;AOB:2.34×105个/g干土);在岸边带湖相区,氨氧化细菌主导氨氧化过程,氨氧化古菌的amoA基因丰度只有氨氧化细菌的1/50倍(AOA:3.17×106个/g干土;AOB:1.39×108个/g干土);在岸边带中间区,两种微生物对氨氧化过程的贡献相当,二者的amoA基因丰度也相当(AOA:9.83×106,AOB:4.08×106)。研究还发现,湿地中间区的微生物生物多样性高于陆相区和湖相区。在湿地中间区,氨氧化古菌和氨氧化细菌的生物多样性都最高,分别有5和7个操作分类单元(OTUs);相比之下,岸边带陆相区和湖相区的多样性依次降低,陆相区的氨氧化古菌和氨氧化细菌分别有3和6个操作分类单元,湖相区的氨氧化古菌和氨氧化细菌分别有2和6个分类单元。所得结论反映了湿地岸边带极强的空间异质性。

The existence and function of ammonia-oxidizing archaea（AOA） in the environment has drawn great interests in recent nitrogen cycle researches.Many previous researches found that AOA dominated ammonia oxidation process in many environments such as ocean,pristine soil and cultivated soils.Wetland system is an important interfacial zone between aquatic and terrestrial ecosystems.Characterized by high biodiversity,strong boundary effects,and combined physicochemical features of the neighbor ecosystems,wetland system plays important roles in material and energy fluxes between these systems.However,very few researches on AOA in wetland systems have been reported.To determine the abundance and distribution of AOA and AOB（short for Ammonia-Oxidizing Bacteria） in lake littoral zones,cultivation-independent methods,such as qPCR,clone and sequencing,were used.Soil samples from different littoral wetland zones of Baiyangdian Lake（site 1 representing for landward zone： four meters from water-soil edge on land;site 2 for middle zone： about 0.5 meter from water-soil edge on land;site 3 for lakeward zone： 1 meter from water-soil edge in sediment of the lake） were sampled and the bacterial and archaeal amoA genes were analyzed.Results show that AOA and AOB dominate the ammonia oxidation in different zones of the littoral wetland in Baiyangdian Lake wetlands.This indicates that the dominate ammonia-oxidizing microorganism changes gradually from AOA to AOB in the wetland ceotone changes from land to water.AOA dominates ammonia oxidation in the landward zone of the wetland,where amoA gene copy numbers of AOA（1.23×108 per gram of dry soil） is 526 times more than that of AOB（2.34×105 per gram of dry soil）.AOB dominates ammonia oxidation in the lakeward zone,where amoA gene copy numbers of AOA（3.17×106 per gram of dry soil） is only 1/50 times of that of AOB（1.39×108 per gram of dry soil）.In the middle zone,AOA and AOB contribute nearly the same for ammonia oxidation,where amoA gene copy numbers of AOA and AOB are in same too（9.83×106 for AOA,4.08×106 for AOB）.It was found that biodiversity of both AOA and AOB amoA gene in the middle zone is high zone with 5 and 7 OTUs（short for Operational Taxonomic Units） separately.In comparison,that in the landward zone only has 3 OTUs for AOA,6 OTUs for AOB,and that in lakeward sediment only has 2 OTUs for AOA,6 OTUs for AOB.High biodiversity of microcosm in wetland shows a similar trend as the high biodiversity of plants,insects and animals reported by other researches.The high biodiversity in wetland boundary zone is probably due to the high energy exchanges,seasonal changed water levers and complicated chemical conditions in this area.