The functioning of Arctic soil ecosystems is crucially important for the global climate. Permafrost soils contain nearly twice as much carbon as the atmosphere and it is assumend that large quantities of carbon are lost (in the form of methane and carbon dioxide) when these soils thaw. Understanding the composition and functioning of the microbial communities in arctic soils is therefore crucial in order to be able to predict their vulnerability and reactions in a changing climate. Nitrification is considered important for ecosystem functioning in the arctic, because the availability of nitrogen, the major limiting nutrient in the system, is directly dependent on it. But the major drivers of nitrification in the arctic are currently unknown. We have recently measured different gross situand potential nitrification rates in arctic soils that were dominated by distinct phylogenetic clades of ammonia oxidizing archaea (AOA) suggesting differences in the activities of various clades and also dominance of AOA over ammonia oxidizing bacteria (AOB) in most soils or even their exclusive presence in some. Furthermore, an enrichment of an arctic AOA of an uncharacterized lineage was obtained that is abundant in the European arctic tundra. overall goal of this proposal is to get insight into the distribution and activity of AOA in arctic ecosystems. To achieve this we will follow two experimental paths: One involves the study of AOA in diverse arctic ecosystems and the second the characterization of Nitrosovradea arctica, an organism representing one of the abundant lineages in arctic soils. will study the distribution and abundance of the six major AOA clades in various arctic soils, using deep sequencing and a clade-specific quantitative PCR assay and will link these to environmental parameters and gross nitrification rates. Samples will be obtained in the frame of two international projects studying terrestrial arctic ecosystems, in which we participate (CryoCarb, ESF) or collaborate (CryoN/PAGE21, EU). The direct and indirect contribution of AOA to NO production and nitrification will be studied in incubation experiments with various inhibitors. Metatranscriptomics will be employed in order to investigate their activity in soils at situand increased temperatures. In the second part of the project, the enrichment culture of the arctic strain will be used to study growth characteristics, inhibitors, and NO emission. Furthermore, the genomic sequence will be determined and transcription studies will be performed in order to analyse adaptations and physiological characteristics. Both project parts will be closely interlinked.
In total, we will contribute to a better understanding of arctic ammonia oxidizers including their direct or indirect influence on nitrification and NO production and we will contribute to a better understanding of the physiology of ammonia oxidizing archaea in general.