Quantitative analyses of ammonia-oxidizing Archaea and bacteria in the sediments of four nitrogen-rich wetlands in China

With the rapid development of ammonia-synthesizing industry, the ammonia-nitrogen pollution in wetlands acting as the sink of point and diffuse pollution has been increased dramatically. Most of ammonia-nitrogen is oxidized at least once by ammonia-oxidizing prokaryotes to complete the nitrogen cycle. Current research findings have expanded the known ammonia-oxidizing prokaryotes from the domain Bacteria to Archaea. However, in the complex wetlands environment, it remains unclear whether ammonia oxidation is exclusively or predominantly linked to Archaea or Bacteria as implied by specific high abundance. In this research, the abundance and composition of Archaea and Bacteria in sediments of four kinds of wetlands with different nitrogen concentration were investigated by using quantitative real-time polymerase chain reaction, cloning, and sequencing approaches based on amoA genes. The results indicated that AOA distributed widely in wetland sediments, and the phylogenetic tree revealed that archaeal amoA functional gene sequences from wetlands sediments cluster as two major evolutionary branches: soil/sediment and sediment/water. The bacteria functionally dominated microbial ammonia oxidation in different wetlands sediments on the basis of molecule analysis, potential nitrification rate, and soil chemistry. Moreover, the factors influencing AOA and AOB abundances with environmental indicator were also analyzed, and the results addressed the copy numbers of archaeal and bacterial amoA functional gene having the higher correlation with pH and ammonia concentration. The pH had relatively great negative impact on the abundance of AOA and AOB, while ammonia concentration showed positive impact on AOB abundance only. These findings could be fundamental to improve understanding of the importance of AOB and AOA in nitrogen and other nutrients cycle in wetland ecosystems.