Abundance, diversity and niche-specific traits of ammonia oxidizers inhabiting soil temporarily flooded by seawater

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Soil nitrification, a key process within numerous natural and agricultural ecosystems, can evoke groundwater pollution and significantly affects plant nutrition as well as greenhouse gas release. The initial and rate-limiting step of this globally important process, ammonia oxidation, is mediated by archaeal and bacterial soil microorganisms. In this project, the impact of seawater flooding frequency on abundance and diversity of these nitrifying prokaryotes, as well as genetic and physiological traits of ammonia oxidizing archaea present in frequently flooded soil, will be investigated. The analyses, comprising culture-based and culture-independent approaches, are carried out on the basis of top soil samples derived from the German Halligen Hooge, Langeness and Nordstrandischmoor. Flooding-related changes in abundance, taxonomic composition as well as species richness of archaeal and bacterial ammonia oxidizers are assessed by quantitative PCR and amplicon sequencing of amoA and 16S rRNA genes isolated from Hallig soil. In order to identify thaumarchaeal genomic characteristics potentially conferring selective advantages within soil frequently swamped by seawater (e.g., genes involved in protection against osmotic stress), construction and screening of complex metagenomic libraries will be performed. Moreover, culturing and growth experiments are conducted to isolate environmentally representative members of archaeal ammonia oxidizers from Hallig soil and to determine their physological adaptations toward frequent flooding. Physiology analyses include the investigation of microbial growth under varying salt, oxygen and ammonia concentrations as soils frequently flooded by sea water represent salty environments characterized by periods of low oxygen availability and nutrient washout. Considering that there is strong evidence for global sea level rise, wetlands occupy approximately 6% of the land area worldwide, and flooded soil environments are often used agriculturally, knowledge on functional microbial groups colonizing soil temporarily swamped by seawater is required to predict and control ecosystem functions within these habitats. The proposed project will contribute to an improved understanding of microbiota controlling nitrification within flooded soils by providing detailed information on quantity, diversity, and niche-specific traits of archaeal and bacterial ammonia oxidizers.