Distribution characteristics of ammonia oxidizing microorganisms in rhizosphere sediments of cattail

The abundance, diversity and community structure of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were investigated, using amoA gene as a molecular biomarker, to examine how cattail (Typha orientalis) growth affects the abundances and communities of AOB and AOA in the rhizosphere sediment. Clone libraries and qPCR (quantitative polymerase chain reaction) results indicated the amoA gene copies numbers, relative abundance of AOA and AOB amoA gene clone libraries were highest in rhizosphere sediment, followed by non-rhizosphere sediment and control, indicating that cattail growth has a remarkable effect on the abundance and community structure of ammonia oxidizing microorganisms. Diversity index (Chao1 and Shannon H) have an obvious variation in cattail rhizosphere, non-rhizosphere and control sediments. The average values of Shannon H of AOA and AOB in the rhizosphere sediment were higher than the non-rhizosphere sediment and control. The average value of Chao1 was highest in non-rhizosphere sediment for AOA, whereas, was highest in the rhizosphere sediment for AOB. The abundance, diversity and community structure of AOA and AOB were obvious different in the cattail's three developmental stages, and higher abundances and more complex community structure were obtained in the maturity stage, which may be attributable to the higher root exudation owing to fast growth rates and strong metabolisms in the maturity stage. In addition, despite higher abundant of AOA versus AOB was demonstrated in the cattail rhizosphere, non-rhizosphere sediment and control, bacteria, not archaeal, have more ecosystem functions and play a more important role in dominating ammonia oxidation under the conditions of this study according to the two findings from the present study. One is that AOB had a more diverse and more complex community structure than AOA; the other is that the average value of potential nitrification rates (PNRs) significantly decreased (by 49.08%, 53.69% and 10.39%, respectively) in rhizosphere, non-rhizosphere sediment and control, as compared to PNRs without the ampicillin, when ammonia-oxidizing bacteria were inhibited by ampicillin.