Nitrification and growth of autotrophic nitrifying bacteria and Thaumarchaeota in the coastal North Sea

[摘要] Nitrification and the associated growth of autotrophic nitrifiers, as wellas the contributions of bacteria and Thaumarchaeota to total autotrophicC-fixation by nitrifiers were investigated in the Dutch coastal North Seafrom October 2007 to March 2008. Rates of nitrification were determined byincubation of water samples with ¹⁵N-ammonium and growth of autotrophicnitrifiers was measured by incubation with ¹³C-DIC (dissolved inorganic carbon) in the presenceand absence of nitrification inhibitors (nitrapyrin and chlorate) incombination with compound-specific stable isotope (¹³C) analysis ofbacterial and Thaumarchaeotal lipid biomarkers. Net nitrification duringthe sampling period was evident from the concentration dynamics of ammonium,nitrite and nitrate. Measured nitrification rates were high (41–221 nmol N L⁻¹ h⁻¹). Ammonium assimilation was always substantially lowerthan nitrification – with nitrification on average contributing 89%(range 73–97%) to total ammonium consumption.

¹³C-DIC fixation into bacterial and Thaumarchaeotal lipids was stronglyreduced by the nitrification inhibitors (27–95 %). The inhibitor-sensitive¹³C-PLFA (phospholipid-derived fatty acid) pool was dominated by the common PLFAs 16:0, 16:1ω7cand 18:1ω7c throughout the whole sampling period and occasionallyalso included the polyunsaturated fatty acids 18:2ω6c and18:3ω3. ¹³C-DIC fixation activity of the nitrifying bacteriawas much higher than that of the nitrifying Thaumarchaeota throughout thewhole sampling period, even during the peak in Thaumarchaeotal abundance andactivity. This suggests that the contribution of autotrophic Thaumarchaeotato nitrification during winter in the coastal North Sea may have beensmaller than expected from their gene abundance (16S rRNA and amoA(ammoniamonooxygenase)). These results emphasize the importance of direct measurements of the actualactivity of bacteria and Thaumarchaeota, rather than abundance measurementsonly, in order to elucidate their biogeochemical importance. The ratiobetween rates of nitrification versus DIC fixation by bacterial nitrifierswas higher or even much higher than typical values for autotrophicnitrifiers, indicating that little DIC was fixed relative to the amount ofenergy that was generated by nitrification.

[学科分类] 地球化学与岩石