我国北方四类土壤中氨氧化古菌和氨氧化细菌的活性及对氨氧化的贡献

氨氧化古菌(ammonia-oxidizing archaea,AOA)与氨氧化细菌(ammonia-oxidizing bacteria,AOB)是目前已知的两类好氧氨氧化微生物,广泛分布于各类生态系统中.采用双氰胺(dicyandiamide;DCD)和1-辛炔(1-octyne)抑制剂的方法对我国北方湿地、草原、农田、沙漠4类生态系统的土壤中AOA和AOB的氨氧化速率(ammonia oxidation rate,AR)分别进行定量测定,剖析AOA、AOB对不同土壤中氨氧化的贡献.结果表明:在氨氮含量较高的湿地土壤((32.58±1.38)mg·kg~(-1))中氨氧化速率由AOB主导(ARAOB占AR的86.19%),而在氨氮含量较低的草原土壤((10.40±0.69)mg·kg~(-1))、农田土壤((5.09±0.25)mg·kg~(-1))中氨氧化速率则由AOA主导(ARAOA分别占AR的65.50%、62.20%).氨氮含量是影响AOA、AOB相对活性的主要限制性因素.湿地土壤中氨氧化速率最高,为3.22 mg·kg~(-1)·d~(-1)(以N计),其次是草原土壤和农田土壤,其AR分别为1.11、1.00 mg·kg~(-1)·d~(-1),沙漠土壤中未检测到氨氧化速率.对氨氧化古菌、细菌的amoA基因进行定量分析的结果表明:在氨氮含量最高的湿地土壤和最低的沙漠土壤((1.27±0.05)mg·kg~(-1))中AOA丰度高于AOB丰度,在草原、农田土壤中AOB丰度高于AOA丰度.amoA基因生物多样性分析表明,377个古菌amoA序列以85%相似度可以划分为19个独立操作单元(operational taxonomic unit,OTU),具有较高的生物多样性,其Shannon指数为1.51~1.73.直接通过氨氧化微生物amoA基因丰度来推测AOA、AOB的活性具有一定的缺陷,而依靠AOA、AOB分别的氨氧化速率能够准确地衡量其在不同生态系统中对氨氮去除的相对贡献,对于理解不同生态系统中氨氮去除过程和效应有着重要的意义.

Activity of AOA and AOB and their contributions to ammonia oxidization in four soils in North China

Ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) are two groups of aerobic microorganisms to oxidize ammonia and exist in various ecosystems. Dicyandiamide (DCD) and 1-octyne inhibition methods were exploited to quantify the ammonia oxidation rates (ARs) of AOA and AOB in soils from wetland, grassland, farmland and desert in North China. Results showed that AOB dominated the ammonia oxidation processes in the wetland soil with ammonia N contents of 32.6 mg·kg^-1, showing the highest AR_AOB of 3.22 mg·kg^-1·d^-1, 86.19% of the total AR. AOA also dominated that in the grassland and farmland soils with less ammonia contents of 10.40 and 5.09 mg·kg^-1, and ARs_AOA of the two soils were 65.5% and 62.2% of the total. Ammonia N content was identified as the key factor influencing the relative roles of ammonia oxidation processes by AOA and AOB. AR was not detected in the desert soil with the lowest ammonia contents (1.27 mg·kg^-1). The number of archaeal amoA genes (genes for potential protein subunit composing the ammonia monooxygenase) was higher than the bacterial amoA genes in the wetland soil with the highest ammonia contents. The amoA gene biodiversity analysis showed that 377 archaeal amoA gene sequences were classified into 19 OTUs at 85% similarity and this suggested a high diversity (Shannon index:1.51~1.73). It is suggested that it is improper to predict the AR by their abundance alone, and the ammonia oxidation rates can evaluate the relative roles of AOA and AOB in different types of ecosystems. These results help to understand the ammonia removal processes in various ecosystems.