Abstract: Invasive plants usually change invaded soil microbial communities which have an important regulatory role in soil nutrient cycling and interspecies competition. Thus, it is important to investigate the effect of invasive plants on native soil microbial communities so as to assess their effect on native ecosystems and the microbial mechanisms involved. In this study, the effect of Flaveria bidentis, an invasive plant, on soil ammonia-oxidizing bacteria (AOB) community was investigated by using polymerase chain reactiondenaturing gradient gel electrophoresis (PCRDGGE). The results showed that most identified AOB were Nitrosospira sp., Nitrosation vibrio, uncultured Nitrosomonas and uncultured AOB in the studied soils, with the domination of Nitrosospira and uncultured AOB. The Shannon indexes of AOB were in order of invaded rhizosphere soil > non-invaded soil > invaded bulk soil, and the soil potential nitrification rate followed the same pattern. Also, both nitrate and ammonium nitrogen contents were correlated closely with the Shannon index. It was concluded that AOB community diversity was reduced following the invasion of F. bidentis with the rhizosphere effect detected, suggesting that F. bidentis might promote its spreading by boosting N-cycling in rhizosphere in the invasion process.

Key words: N₂O, soil organic carbon, intercropping, legume., CO₂