三种利用方式对羊草草原土壤氨氧化细菌群落结构的影响

本文以内蒙古呼伦贝尔羊草草原为研究对象，利用聚合酶链式反应－变性梯度凝胶电泳(PCR－DGGE)技术及扩增产物序列分析方法比较研究了刈割、放牧和围栏封育三种利用方式对羊草草原土壤氨氧化细菌多样性和系统发育的影响，结果表明：羊草草原土壤中氨氧化细菌的优势类群为亚硝化螺旋菌属和亚硝化单孢菌属的细菌，分别占氨氧化细菌总数的72.4%和28.6%，Cluster 4和Cluster 6在各个样地中均为优势类群但所占比例不同，放牧样地中氨氧化细菌的多样性最高，逐步回归分析的结果表明，影响多样性指数的关键理化因子是土壤硝态氮含量。放牧样地中脲酶活性和硝化率都显著高于其他两种利用方式，其中，脲酶活性与土壤硝态氮和全磷含量表现出极显著的相关性，与速效磷含量表现出显著相关性；而硝化率仅与硝态氮含量表现出显著相关性。不同利用方式土壤氨氧化细菌群落与土壤理化因子的典范对应分析结果表明铵态氮的含量对氨氧化细菌群落的影响显著。

Effects of three land use patterns on diversity and community structure of soil ammonia-oxidizing bacteria in Leymus chinensis steppe

Available nitrogen is not only one of the most important limitation resources to manipulate primary productivity,but also a major factor to decide species composition in a grassland ecosystem.Chemolithotrophic nitrification is a two-step process,consisting of the conversion of ammonia to nitrite then further to nitrate.Those steps are involved two different groups of organisms,the ammonia-oxidizing bacteria(AOB) and the nitrite-oxidizing bacteria(NOB),respectively.In this study,the active AOB community was investigated by using approaches of polymerase chain reaction-denaturing gradient gel electrophoresis(PCR-DGGE) and sequences analysis on the Leymus chinensis steppes with three of mowing,grazing and fencing treatments respectively in Hulunbeier steppe of Inner Mongolia.Sampling in August 2008 when vegetation was at its best condition.Samples were taken at depths of 0—0.20m.The community structure and diversity of the bacterial groups from the different samples was further analyzed by using different techniques,such as statistical analysis and diversity index evaluation of the band patterns etc.The results showed that grazing activity significantly increased the number of species and quantities of AOB,as well as the diversity.A total of 21 sequences representing 21 different sequence types were recovered from the DGGE gels after phylogenetic reconstructions.The results further revealed that most sequences were coming from Nitrosospira and Nitrosomonas of β-Proteobacteria,with accounting for 72.4% and 28.6% respectively.Cluster 4 of Nitrosospira existed in grazing,mowing and fencing plots with accounting for 25.0%,27.2% and 26.3% respectively in their dominant AOB.And Cluster 6 of Nitrosomonas existed in grazing,mowing and fencing plots,those accounted for 33.1%,18.1% and 21.1% respectively in their dominant AOB.Analyze of stepwise regression showed that the key soil physicochemical factor which influence the diversity index most is the content of nitrate nitrogen.Urease activity and nitrate rate in grazing plot were both higher than the other land use patterns.The content of nitrate nitrogen and total phosphorus were both extremely significant(P<0.01) correlated with urease activity,and there is a significant(P<0.05) relationship between urease activity and the content of available phosphorus;at the same time,there is also a significant relationship between nitrate rate and nitrate nitrogen contents.AOB communities in Leymus chinensis steppe were significantly(P<0.05) influenced by the levels of ammonium nitrogen when canonical correspondence analysis was employed to identify relationship between AOB and soil physicochemical factors under different land use patterns.Based on the above findings,it seems that nitrogen cycles represent the key links between above and below ground ecosystems.Land use patterns in Leymus chinensis steppe have significant and long-term impacts on the size and the structure of the soil AOB community at both phylogenetic and functional levels,thus would further affect the transformation and utilization of nitrogen in the steppe ecosystem.