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Activity and diversity of a phylogenetically novel acid-tolerant nitrate reducer communities in an N2O-emitting fen

Katharina Palmer1, Harold Drake, Marcus Horn
1 Lehrstuhl für Ökologische Mikrobiologie, Universität Bayreuth

O 1.7 in Funktion von Ökosystemen

02.04.2009, 12:00-12:15, H8

Wetlands are sources of the greenhouse gas N2O. The nitrate reducers (i.e. denitrifies and dissimilatory nitrate reducers) potentially linked to the emission of N2O by a regional acidic fen (pH 4.2-5.5) were evaluated. Total cell counts and MPN-counts of denitrifiers from 0-10 cm and 30-40 cm fen depths approximated 1011 cells per gram dry weight and 108 cells per gram dry weight, respectively. The analysis of narG (coding for the dissimilatory nitrate reductase of nitrate reducers) and nosZ (coding for the N2O reductase of denitrifiers) indicated a highly diverse and hitherto unknown nitrate reducer community. narG and nosZ were grouped into 16 and 18 presumably species level OTUs, respectively, and formed distinct phylogenetic clusters. tRFLP analyses of narG and nosZ revealed minor differences in community composition of nitrate reducers and denitrifiers in different soil depths (0-40 cm). The highest nitrate reducer and denitrifier diversity as well as the estimated species richness were found in the upper soil layers (0-20 cm). Fen soil produced and consumed N2O in unsupplemented anoxic microcosms. Supplemental nitrate stimulated complete denitrification. Denitrification rates decreased with depth. Despite similar MPN values obtained for each soil depth, Vmax values for different depths ranged from 1 to 24 nmol N2O per hour and gram dry weight. Denitrification occurred at 2-60 °C and at pH 2.0-6.5 with highest rates at in situ pHs (i.e., at pH 4-5). N2O approximated 40% of total produced N gases at in situ pH. Formate, acetate, and ethanol enhanced denitrification. Nitrate reducers capable of N2O-production were isolated from the fen. N2O was consumed by soils in anoxic microcosms supplemented with N2O ranging from sub-atmospheric concentrations to 0.2% (v/v). The collective data indicate that (i) a novel highly diverse denitrifier community capable of complete denitrification and consumption of atmospheric N2O at in situ pH occurs in acidic fens and (ii) novel, acid-tolerant nitrate reducers might contribute to N2O emission.

Letzte Änderung 08.03.2009