title: Genetic and environmental controls on nitrous oxide accumulation in lakes.
abstract: We studied potential links between environmental factors, nitrous oxide (N2O) accumulation, and genetic indicators of nitrite and N2O reducing bacteria in 12 boreal lakes. Denitrifying bacteria were investigated by quantifying genes encoding nitrite and N2O reductases (nirS/nirK and nosZ, respectively, including the two phylogenetically distinct clades nosZI and nosZII) in lake sediments. Summertime N2O accumulation and hypolimnetic nitrate concentrations were positively correlated both at the inter-lake scale and within a depth transect of an individual lake (Lake Vanajavesi). The variability in the individual nirS, nirK, nosZI, and nosZII gene abundances was high (up to tenfold) among the lakes, which allowed us to study the expected links between the ecosystem's nir-vs-nos gene inventories and N2O accumulation. Inter-lake variation in N2O accumulation was indeed connected to the relative abundance of nitrite versus N2O reductase genes, i.e. the (nirS+nirK)/nosZI gene ratio. In addition, the ratios of (nirS+nirK)/nosZI at the inter-lake scale and (nirS+nirK)/nosZI+II within Lake Vanajavesi correlated positively with nitrate availability. The results suggest that ambient nitrate concentration can be an important modulator of the N2O accumulation in lake ecosystems, either directly by increasing the overall rate of denitrification or indirectly by controlling the balance of nitrite versus N2O reductase carrying organisms.
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä, 40014, Jyväskylä, Finland.
authors.forename: Jatta
authors.initials: J
authors.lastname: Saarenheimo
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä, 40014, Jyväskylä, Finland.
authors.forename: Antti J
authors.initials: AJ
authors.lastname: Rissanen
authors.affiliation: Lammi Biological Station, University of Helsinki, 16900, Lammi, Finland.
authors.forename: Lauri
authors.initials: L
authors.lastname: Arvola
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä, 40014, Jyväskylä, Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Nykänen
authors.affiliation: Department for Environmental Science, University of Basel, CH-4058, Basel, Switzerland.
authors.forename: Moritz F
authors.initials: MF
authors.lastname: Lehmann
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä, 40014, Jyväskylä, Finland.
authors.forename: Marja
authors.initials: M
authors.lastname: Tiirola
mesh_terms: D001419:Bacteria / Q000145:classification / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D058440:Denitrification; D017753:Ecosystem; D015964:Gene Expression Regulation, Bacterial; D060106:Lakes / Q000737:chemistry* / Q000382:microbiology; D009572:Nitrite Reductases / Q000235:genetics*; D009609:Nitrous Oxide / Q000737:chemistry*; D010088:Oxidoreductases / Q000235:genetics*; D012621:Seasons; D014871:Water Microbiology
chemical_list: D001426:Bacterial Proteins; D010088:Oxidoreductases; D009572:Nitrite Reductases; C022763:nitrous oxide reductase; D009609:Nitrous Oxide