Background
Nitrogen is the critical limiting nutrient of many coastal ecosystems, including mangrove forest as one of the most important integrated ecosystems mainly distributed in the tropical or subtropical coastline and estuary areas. The microorganisms inhabiting mangrove forests play important roles in driving the cycling of nutrients including nitrogen. Increasing researches have been focusing on the spatial distribution pattern, potential biogeochemical functions, and the relationship with environmental factors of N transforming microorganisms.
Research goals
To find out the niche specificity of key functional genes of the nitrogen cycle along with the sediment depths in two sediment types, mangrove covering field and intertidal mudflats without tree from coastal Mai Po wetland of Hong Kong.
Methods:
Random shotgun sequencing, metagenomics, de novo genome assembly, functional genes searching.
Results
We found that, for most of the key N functional genes, their diversity decreased with depths. Except for some occasions, nifH, narG and norC genes in mangrove sediment reached the highest diversity in the middle layers (5-10 cm). Besides, there were no differences in genes diversity between the two sediment types except for nirK gene, which showed a higher diversity in mangrove sediment than that in tidal mudflat sediment. The amoA genes for ammonia oxidization were hardly found in deeper layer of sediments at both sites.
Discussion and implications of the findings
Our preliminary results have suggested further investigation should be performed to explore whether a certain taxonomic group of functional genes dominate the microbial community even with a diversity loss with depths, in other words, "how nitrogen cycling function and service relate to diversity?", which could help us to better understand the nitrogen cycle in coastal sediment ecosystems.
