Molecular analysis of ammonia oxidizing prokaryotes in mangrove wetlands and factors affecting their dynamics

Abstract

Ammonia/ammonium-oxidizing prokaryotes (AOPs) play a crucial role in nitrogen transformation in the natural ecosystems including mangrove wetlands. The objectives of the present study were to investigate the spatial and temporal distribution of AOPs in the mangrove wetland sediments in subtropical Hong Kong and their ecophysiology.

When AOP communities and abundances in a natural coastal mangrove wetland and a constructed freshwater wetland were compared, the constructed freshwater wetland contained a broader range of phylotypes, higher diversity, more complex community structures, and more uneven abundances of AOPs than the mangrove wetland. Typha angustifolia affected the community structures of all AOPs and enhanced their abundances in the rhizosphere. Both Phragmites australis and Cyperus malaccensis showed some effects on the community structures of ammonia-oxidizing bacteria (AOB), but little effects on those of anaerobic ammonium oxidizing (anammox) bacteria or ammonia-oxidizing archaea (AOA). Kandelia obovata had no detectable effect on any group of the AOPs due to their smaller size.

AOPs in oxic and anoxic sediments of a protected mangrove wetland were investigated in both winter and summer. Seasonality had little effect on community structure and abundance of anammox bacteria. AOA community structures were stable between the two seasons, but AOA abundance was significantly higher in winter than summer. The community structures of AOB were different between winter and summer, but the abundance in winter was apparently higher than that in summer. Sediment type had a noticeable influence on community structure and abundance of anammox bacteria. No apparent difference in AOA community structures between the different types of sediments in winter was observed, but the oxic sediments showed obviously different AOA community structures from anoxic sediments in summer. Sediment type had little effect on AOB community structures, but AOB abundance in oxic sediments was obviously lower than anoxic ones in both seasons.

Addition of acetate or leaf litter into sediment inhibited the growth of anammox bacteria in laboratory incubation. The inhibition of anammox bacteria by acetate was more pronounced than by leaves. Acetate and leaf litter did not affect AOA community structures, but promoted their growth. Both acetate and leaf litter affected the AOB community structures and promoted their growth in the early phase of the incubation. The promoting effects by leaf litter were more obvious than by acetate.

Allylthiourea effectively inhibited the growth of both AOA and AOB in laboratory incubation, but only slightly for anammox bacteria. Acidic condition altered AOB community structure, but affected anammox bacteria and AOA slightly. Alkaline condition strongly affected community structures of anammox bacteria and AOA, but slightly for AOB. Alkaline condition inhibited the growth of anammox bacteria, but promoted AOA and AOB slightly. Increase in salinity resulted in higher diversity of anammox bacteria, and AOA and AOB might have species specific preference for salinity. High salinity promoted anammox bacteria growth; inhibited AOA for 5-10 days, but promoted them afterward; and promoted AOB. Totally, this study revealed new and specific information on the spatial and temporal distribution of AOPs in mangrove wetland and factors affecting their ecophysiology.