title: Water addition regulates the metabolic activity of ammonia oxidizers responding to environmental perturbations in dry subhumid ecosystems.
abstract: Terrestrial arid and semi-arid ecosystems (drylands) constitute about 41% of the Earth's land surface and are predicted to experience increasing fluctuations in water and nitrogen availability. Mounting evidence has confirmed the significant importance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in nitrification, plant nitrogen availability and atmospheric N2 O emissions, but their responses to environmental perturbations in drylands remain largely unknown. Here we evaluate how the factorial combinations of irrigation and fertilization in forests and land-use change from grassland to forest affects the dynamics of AOA and AOB following a 6-year dryland field study. Potential nitrification rates and AOA and AOB abundances were significantly higher in the irrigated plots, accompanied by considerable changes in community compositions, but their responses to fertilization alone were not significant. DNA-stable isotope probing results showed increased (13) CO2 incorporation into the amoA gene of AOA, but not of AOB, in plots receiving water addition, coupled with significantly higher net mineralization and nitrification rates. High-throughput microarray analysis revealed that active AOA assemblages belonging to Nitrosopumilus and Nitrosotalea were increasingly labelled by (13) CO2 following irrigation. However, no obvious effects of land-use changes on nitrification rates or metabolic activity of AOA and AOB could be observed under dry conditions. We provide evidence that water addition had more important roles than nitrogen fertilization in influencing the autotrophic nitrification in dryland ecosystems, and AOA are increasingly involved in ammonia oxidation when dry soils become wetted.
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Penrith South DC, NSW, 2751, Australia; State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China.
authors.forename: Hang-Wei
authors.initials: HW
authors.lastname: Hu
authors.forename: Catriona A
authors.initials: CA
authors.lastname: Macdonald
authors.forename: Pankaj
authors.initials: P
authors.lastname: Trivedi
authors.forename: Bronwyn
authors.initials: B
authors.lastname: Holmes
authors.forename: Levente
authors.initials: L
authors.lastname: Bodrossy
authors.forename: Ji-Zheng
authors.initials: JZ
authors.lastname: He
authors.forename: Brajesh K
authors.initials: BK
authors.lastname: Singh
mesh_terms: D057914:Agricultural Irrigation; D000641:Ammonia / Q000378:metabolism*; D001105:Archaea / Q000235:genetics / Q000378:metabolism; D001419:Bacteria / Q000235:genetics / Q000378:metabolism; D017753:Ecosystem; D005308:Fertilizers; D065948:Grassland; D058465:Nitrification; D009584:Nitrogen / Q000378:metabolism*; D058458:Nitrogen Cycle; D010084:Oxidation-Reduction; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D014197:Trees / Q000382:microbiology; D014867:Water / Q000378:metabolism
chemical_list: D005308:Fertilizers; D012987:Soil; D014867:Water; D000641:Ammonia; D009584:Nitrogen