Abstract
Mangroves are ecosystems located in the transition zone between land and sea, characterized by periodic flooding that confer to its unique characteristics. Little is known about the transformation of nutrients that occur during the organic matter degradation in this system. In this study, we monitor the nitrogen transformations in soils from three mangroves with distinct levels of contamination using labeled 15NO3-. We also screened the mangroves metagenomes for the presence of genes that encode enzymes involved in denitrification (nirS, nirK, nosZ, norB and narG), anaerobic oxidation of ammonia (anammox) (hh, hao and hzo) and dissimilatory nitrate reduction to ammonium (DNRA) (nrfA). The transformations of 15NO3- indicated the balance of denitrification over anammox and DNRA in all three mangroves, with lower rates of processes in the mangrove affected by oil contamination. The metagenomic analysis detected 56 sequences related to denitrification, 19 with anammox and 6 with DNRA. Genes related with denitrification were phylogenetically distributed among several groups of bacteria (mainly Gammaproteobacteria). Anammox and DNRA related sequences were affiliated with Planctomycetes and Gammaproteobacteria, respectively. Thus, metagenomic and functional approaches supported the description of denitrification, anammox and DNRA rates in mangrove soils, and identified the major bacterial groups involved in these processes.
Highlights
Mangroves are important coastal ecosystems found in transition zones between marine and freshwater ecosystems such as estuaries, bays, and lagoons (Holguin et al 1999, 2001)
Total nitrogen, total carbon, organic carbon, total sulphur and conductivity tended to be higher in BrMgv02 (Table I)
In this study, we performed experiments with labeled nitrogen (15N) compounds and metagenomics to better understand the actual rates of the nitrogen cycling processes, denitrification, anammox and dissimilatory nitrate reduction to ammonium (DNRA)
Summary
Mangroves are important coastal ecosystems found in transition zones between marine and freshwater ecosystems such as estuaries, bays, and lagoons (Holguin et al 1999, 2001) These ecosystems constitute a large portion (60–70%) of the coastline in the tropical and subtropical regions (Sahoo and Dhal 2009), and play a major socio-economic role to human communities in developing countries. The microbial community present in mangrove soils is strongly influenced by biogeographical, anthropogenic, and ecological properties, including the food web in the ecosystem, nutrient cycling, and the presence of organic and inorganic compounds in the sediment (Ghosh et al 2010). The high litterfall, its degradation and re-mineralization, is one of the factors contributing to high nitrogen concentrations in mangrove soils (Fernandes et al 2012)
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