title: Carbon amendment and soil depth affect the distribution and abundance of denitrifiers in agricultural soils.
abstract: The nitrite reductase (nirS and nirK) and nitrous oxide reductase-encoding (nosZ) genes of denitrifying populations present in an agricultural grassland soil were quantified using real-time polymerase chain reaction (PCR) assays. Samples from three separate pedological depths at the chosen site were investigated: horizon A (0-10 cm), horizon B (45-55 cm), and horizon C (120-130 cm). The effect of carbon addition (treatment 1, control; treatment 2, glucose-C; treatment 3, dissolved organic carbon (DOC)) on denitrifier gene abundance and N2O and N2 fluxes was determined. In general, denitrifier abundance correlated well with flux measurements; nirS was positively correlated with N2O, and nosZ was positively correlated with N2 (P < 0.03). Denitrifier gene copy concentrations per gram of soil (GCC) varied in response to carbon type amendment (P < 0.01). Denitrifier GCCs were high (ca. 10(7)) and the bac:nirK, bac:nirS, bac:nir (T) , and bac:nosZ ratios were low (ca. 10(-1)/10) in horizon A in all three respective treatments. Glucose-C amendment favored partial denitrification, resulting in higher nir abundance and higher N2O fluxes compared to the control. DOC amendment, by contrast, resulted in relatively higher nosZ abundance and N2 emissions, thus favoring complete denitrification. We also noted soil depth directly affected bacterial, archaeal, and denitrifier abundance, possibly due to changes in soil carbon availability with depth.
authors.affiliation: Microbial Ecology Laboratory, Microbiology, School of Natural Sciences & Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland.
authors.forename: M
authors.initials: M
authors.lastname: Barrett
authors.affiliation: Crops, Environment and Land-Use Department, Teagasc, Johnstown Castle, Co., Wexford, Ireland.
authors.forename: M I
authors.initials: MI
authors.lastname: Khalil
authors.affiliation: Crops, Environment and Land-Use Department, Teagasc, Johnstown Castle, Co., Wexford, Ireland.
authors.forename: M M R
authors.initials: MM
authors.lastname: Jahangir
authors.affiliation: School of Civil & Environmental Engineering Nanyang Technological University, Singapore, 639798, Singapore.
authors.forename: C
authors.initials: C
authors.lastname: Lee
authors.affiliation: Rothamsted Research, North Wyke, Okehampton, Devon, EX20 2SB, UK.
authors.forename: L M
authors.initials: LM
authors.lastname: Cardenas
authors.affiliation: Microbial EcoEngineering Laboratory, Microbiology, School of Natural Sciences & Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland.|Environmental Engineering Laboratory, School of Engineering, University of Glasgow, Rankine Building, Oakfield Avenue, Glasgow, G12 8LT, UK.
authors.forename: G
authors.initials: G
authors.lastname: Collins
authors.affiliation: Crops, Environment and Land-Use Department, Teagasc, Johnstown Castle, Co., Wexford, Ireland.
authors.forename: K G
authors.initials: KG
authors.lastname: Richards
authors.affiliation: Microbial Ecology Laboratory, Microbiology, School of Natural Sciences & Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland. vincent.oflaherty@nuigalway.ie.
authors.forename: V
authors.initials: V
authors.lastname: O'Flaherty
mesh_terms: D000383:Agriculture; D001419:Bacteria / Q000187:drug effects / Q000235:genetics; D002244:Carbon / Q000494:pharmacology*; D058440:Denitrification; D065948:Grassland; D009572:Nitrite Reductases / Q000235:genetics; D009584:Nitrogen / Q000032:analysis; D009609:Nitrous Oxide / Q000032:analysis; D010088:Oxidoreductases / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology
chemical_list: D012987:Soil; D002244:Carbon; D010088:Oxidoreductases; D009572:Nitrite Reductases; C022763:nitrous oxide reductase; D009609:Nitrous Oxide; D009584:Nitrogen
keywords: Denitrification; N2O/N2 emissions; Subsoil; nirK; nirS; nosZ