Abundance, diversity and niche-specific traits of ammonia oxidizers inhabiting soil temporarily flooded by seawater
Final Report Abstract
The Halligen, islands inundated with seawater in different frequency over the year, allowed extensive investigation of ammonia oxidizers colonizing temporarily flooded soil. In accordance with our first hypothesis, ammonia oxidizing archaea outnumbered their betaproteobacterial counterparts in rarely as well as in rather frequently flooded soil. Nevertheless, detection of Nitrosococcus suggests that besides these microbial groups gammaproteobacterial ammonia oxidizers contribute to nitrification in soil temporarily inundated with seawater. With respect to soil exposed to seawater at a high frequency, indigenous ammonia oxidizers exhibited tolerance toward a wide range of salinities (e.g., Wadden Sea water salinity), supporting our second hypothesis. Furthermore, the community composition of both, archaeal and bacterial ammonia oxidizers, was significantly affected by seawater flooding. In line with our third and fourth hypothesis, increased abundances of archaeal and bacterial ammonia oxidizers typically occurring in marine environments were detected in soil derived from the most frequently flooded island. Seawater flooding significantly affects soil salinity and pH which probably strongly contributed to selection of detected ammonia oxidizers in the analyzed samples. Our results indicate that potential future sea level rise and an associated increase in flooding of coastal soils will enrich ammonia oxidizers affiliated to Nitrosopumilus or Nitrosococcus, comprising many representatives tolerating seawater salinity and slightly alkaline pH. The ammonia oxidizers cultured from soil temporarily flooded by seawater are extremely valuable for investigation of mechanisms enabling tolerance to e.g., changes in salinity. Genomic analyses of these microbes are required to identify genes potentially involved in responses to osmotic stress.
