Palmer, K; Horn, MA: Denitrification Activity of a Remarkably Diverse Fen Denitrifier Community in Finnish Lapland Is N-Oxide Limited, PLoS ONE, 10(4), e0123123 (2015), doi:10.1371/journal.pone.0123123
Peatlands cover more than 30% of the Finnish land area and impact N2Ofluxes. Denitrifiers release N2Oas an intermediate or end product. In situ N2Oemissions of a near pH neutral pristine fen soil in Finnish Lapland were marginal during gas chamber measurements. However, nitrate and ammonium fertilization significantly stimulated in situ N2Oemissions. Stimulation with nitrate was stronger than with ammonium. N2Owas produced and subse- quently consumed in gas chambers. In unsupplemented anoxic microcosms, fen soil pro- duced N2Oonly when acetylene was added to block nitrous oxide reductase, suggesting complete denitrification. Nitrate and nitrite stimulated denitrification in fen soil, and maximal reaction velocities (vmax) of nitrate or nitrite dependent denitrification where 18 and 52 nmol N2Oh-1 gDW -1, respectively. N2Owas below 30% of total produced N gases in fen soil when concentrations of nitrate and nitrite were<500 μM. vmax for N2Oconsumption was up to 36 nmol N2Oh-1 gDW -1. Denitrifier diversity was assessed by analyses of narG, nirK/nirS, and nosZ (encoding nitrate-, nitrite-, and nitrous oxide reductases, respectively) by barcod- ed amplicon pyrosequencing. Analyses of ~14,000 quality filtered sequences indicated up to 25 species-level operational taxonomic units (OTUs), and up to 359 OTUs at 97% se- quence similarity, suggesting diverse denitrifiers. Phylogenetic analyses revealed clusters distantly related to publicly available sequences, suggesting hitherto unknown denitrifiers. Representatives of species-level OTUs were affiliated with sequences of unknown soil bac- teria and Actinobacterial, Alpha-, Beta-, Gamma-, and Delta-Proteobacterial sequences. Comparison of the 4 gene markers at 97% similarity indicated a higher diversity of narG than for the other gene markers based on Shannon indices and observed number of OTUs. The collective data indicate (i) a high denitrification and N2Oconsumption potential, and (ii) a highly diverse, nitrate limited denitrifier community associated with potential N2Ofluxes in a pH-neutral fen soil.
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