Diverse nirS-type Denitrifying Bacteria Contribute to Vital Nitrogen Loss in Natural Acidic Red Soils.

Denitrifying bacteria, playing a key role in nitrogen removal in ecosystem, are highly diverse and complex in their community composition. However, there were few reports on the abundance, community composition, and the contribution to nitrogen loss of denitrifiers in natural acidic red soils. In this study, we investigated the structure and function of nirS-type denitrifying bacteria in ten natural red soil samples collected from nine provinces in southern China, based on quantitative polymerase chain reaction (qPCR) and high-throughput sequencing techniques. Nitrogen loss from microbial denitrification in red soils of southern China was estimated up to 9.86 Tg N per year based on 15N isotope tracing method. The abundance of nirS-type denitrifiers varied from 8.41 × 105 to 2.55 × 109 copies per gram of dry weight. The community of nirS-type denitrifying bacterial was revealed, which contained 50 dominant OTUs assigned to 9 clusters phylogenetically related to Marinobacter, Rhodobacter, and other uncultured species. pH was the key factor affecting both denitrification rates and community composition. Our results demonstrate that nirS-type denitrifying bacteria have higher abundance, diversity, and contribution to the nitrogen loss in natural acidic red soils of southern China.