| With the expansion of human activity along riverine and coastal shorelines, mangroves are subject to anthropogenic inputs, which add additional nitrogen to mangrove ecosystems. Mangroves which located in the boundary between the sea and the land were concerned as anatural denitrification systems. In the present study, both traditional cultivation and molecular method were used to investigate the abundance, community structure of nitrifiers and denitrifiers and their nitrification and denitrification abilities in Mai Po mangrove sediment, Hong Kong.7 heterotrophic nitrifying bacteria were isolated from Mai Po mangrove wetland, they were Diaphorobacter sp., Paracoccus sp., Ochrobactrum sp., Sinorhizobium sp., Pseudomonas sp. and Hydrogenophaga sp.. All had high abilities to remove NH＋-N. The removal of NH＋-N by 6 heterotrophic nitrifying bacteria reached 80% within 2 days, while the rest one NWTT was 40.80% within 2 days, but it was 96.65% on the third day. In this study, two strains of NYMO and NYTE were heterotrophic nitrifying-aerobic denitrifying strains, the abilities to remove NH4+-N and NO3--N by NYMO were 34.60% and 33.40%, respectively, while their removal percentages were 35.08% (NH4+-N) and 99.92% (NO3--N) by NYTE.Twenty aerobic and anaerobic denitrifying bacteria strains were obtained, which belonged to Comamonas,Pseudomonas,Thauera,Agrobacterium,Acinetobacter,Ochrobactrum,Hydrogenophaga,Alcaligenes and Unculturedβ—proteobacterium.7 aerobic denitrifiers and 8 anaerobic denitrifiers had the ability to remove 98% NO3--N in 2 days. The effect of oxygen concentrations on N2O production was investigated using strain HWTT as the model bacterium. Results showed that N2O was 35.71μmol and N2O/(N2O+N2) was >70% in aerobic conditions, while the production of N2O decreased to 0.15μmol and N2O/(N2O+N2) was reduced to<0.15% in insufficient oxygen conditions.The results of AOB (Ammonia Oxidizing Bacteria) and NOB (Nitrite Oxidizing Bacteria) 16S rDNA gene clone libraries indicated that, AOB clones belonged to 5 groups: Nitrosospira (40.30%),β-proteobacterium (28.36%), Nitrosomona (14.93%), the ammonia-oxidizing bacterium (11.94%) and Nitrosomonadaceae (4.48%), while 36 clones belonged to several different bacterial groups in the 66 NOB clones, the others were as follows:δ-proteobacterium (22.73%),α-proteobacterium (16.67%), Nitrospira (6.06%) and unknowns (4.56%). To investigate the diversity of denitrifying bacteria in mangrove sediments, a nosZ gene clone library was constructed. Twenty-six clones belonged to 11 unknown groups in the 50 clones, the others were as follows:Pennisetum (26%),β—proteobacterium (10%), Entandrophragma (4%), Pseudomonas (4%) and the denitrifying bacterium (4%), which indicated that Mai Po mangrove had a high degree of taxonomic diversity of denitrifiers.DGGE technique was used to investigate the community structure of AOB. According to DGGE picture and intensity diagram, Nitrosospira sp. was the dominant AOB in Mai Po mangrove wetland; the community structure of AOB varied to tidal conditions; seasonal change was not a factor contributing to the changes of community structure of AOB in low-tide sediments, but a factor contributing to the community structure change of AOB at high-tide sediments.It was concluded that:(1) Mai Po mangrove had a high degree of taxonomic diversity of nitrifiers and denitrifiers; (2) Nitrosospira sp. was the dominating AOB in Mai Po mangrove; (3)δ-proteobacterium andα-proteobacterium were dominant NOB groups; (4) Pseudomonas was one of the primary denitrifiers. |
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