Anaerobic ammonium oxidation and its contribution to nitrogen removal in China's coastal wetlands

Abstract

Over the past several decades, human activities have caused substantial enrichment of reactive nitrogen in China's coastal wetlands. Although anaerobic ammonium oxidation (anammox), the process of oxidizing ammonium into dinitrogen gas through the reduction of nitrite, is identified as an important process for removing reactive nitrogen, little is known about the dynamics of anammox and its contribution to nitrogen removal in nitrogen-enriched environments. Here, we examine potential rates of anammox and associate them with bacterial diversity and abundance across the coastal wetlands of China using molecular and isotope tracing techniques. High anammox bacterial diversity was detected in China's coastal wetlands and included Candidatus Scalindua, Kuenenia, Brocadia, and Jettenia. Potential anammox rates were more closely associated with the abundance of anammox bacteria than to their diversity. Among all measured environmental variables, temperature was a key environmental factor, causing a latitudinal distribution of the anammox bacterial community composition, biodiversity and activity along the coastal wetlands of China. Based on nitrogen isotope tracing experiments, anammox was estimated to account for approximately 3.8-10.7% of the total reactive nitrogen removal in the study area. Combined with denitrification, anammox can remove 20.7% of the total external terrigenous inorganic nitrogen annually transported into China's coastal wetland ecosystems.

Figure 1. Study area and sampling sites.

In this study, eleven sampling sites S1-S11 were selected along the coastal wetlands of China. The map was created with ArcGIS 10.1.

Figure 2

Spatiotemporal variations of anaerobic ammonium oxidation (anammox) rates (a) and associated contribution (b) to nitrogen loss at each sampling site. Vertical bars indicate standard error (n = 3).

Figure 3. UniFrac weighted PCoA analysis of anaerobic ammonium oxidation (anammox) bacterial assemblages as revealed by the 16S rRNA gene sequences.

S and W in parentheses represent summer and winter samples, respectively.

Figure 4. Spatiotemporal variations of anaerobic ammonium oxidation (anammox) bacterial abundance targeting on the 16S rRNA gene in China’s coastal wetland sediments.

Vertical bars indicate standard error (n = 3).

Figure 5. Spatiotemporal variations of dentirification, nitrification, and dissimilatory nitrate reduction to ammonium (DNRA) rates at each sampling site.

Vertical bars indicate standard error (n = 3).

Figure 6. Pearson’s correlations of anaerobic ammonium oxidation (anammox) rates with denitrification, nitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates in China’s coastal wetlands.

Vertical and horizontal bars indicate standard error (n = 3).