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

土壤硝化作用是众多自然和农业生态系统中的一个关键过程，它会引起地下水污染，并对植物营养和温室气体排放产生重大影响。氨氧化这个全球重要过程的初始和限速步骤是由古生菌和细菌土壤微生物介导的。在本项目中，将研究海水淹水频率对这些硝化原核生物丰度和多样性的影响，以及频繁淹水土壤中存在的氨氧化古菌的遗传和生理特性。这些分析包括基于文化的方法和独立于文化的方法，基于来自德国Halligen Hooge，Langness和Nordstranchmoor的表层土壤样本。通过定量聚合酶链式反应和16S rRNA扩增序列测定了从哈里格土壤中分离的amoA和16S rRNA基因，评估了与淹水有关的古细菌和细菌氨氧化菌的丰度、分类组成和物种丰富度。为了确定在经常被海水淹没的土壤中可能具有选择优势的古生菌基因组特征(例如，参与防御渗透胁迫的基因)，将进行复杂元基因组文库的构建和筛选。此外，还进行了培养和生长实验，以从哈利格土壤中分离出具有环境代表性的古氨氧化菌成员，并确定它们对频繁洪涝的生理适应能力。生理学分析包括调查不同盐分、氧气和氨浓度下的微生物生长，因为经常被海水淹没的土壤代表着以氧气利用率低和养分流失为特征的盐碱化环境。考虑到有强有力的证据表明全球海平面上升，湿地约占全球陆地面积的6%，淹没的土壤环境经常被农业利用，因此需要关于功能微生物群的知识来预测和控制这些生境中的生态系统功能。拟议的项目将通过提供有关古细菌和细菌氨氧化菌的数量、多样性和生态位特定特征的详细信息，有助于更好地了解微生物区系控制淹水土壤中的硝化作用。

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.