Biphasic Behavior of Anammox Regulated by Nitrite and Nitrate in an Estuarine Sediment
2005
Trimmer, Mark | Nicholls, Joanna C. | Morley, Nicholas | Davies, Christian A. | Aldridge, John
The production of N₂ gas via anammox was investigated in sediment slurries at in situ NO₂⁻ concentrations in the presence and absence of NO₃⁻. With single enrichment above 10 [micro]M ¹⁴NO₂⁻ or ¹⁴NO₃⁻ and ¹⁵NH₄⁺, anammox activity was always linear (P < 0.05), in agreement with previous findings. In contrast, anammox exhibited a range of activity below 10 [micro]M NO₂⁻ or NO₃⁻, including an elevated response at lower concentrations. With 100 [micro]M NO₃⁻, no significant transient accumulation of NO₂⁻ could be measured, and the starting concentration of NO₂⁻ could therefore be regulated. With dual enrichment (1 to 20 [micro]M NO₂⁻ plus 100 [micro]M NO₃⁻), there was a pronounced nonlinear response in anammox activity. Maximal activity occurred between 2 and 5 [micro]M NO₂⁻, but the amplitude of this peak varied across the study (November 2003 to June 2004). Anammox accounted for as much as 82% of the NO₂⁻ added at 1 [micro]M in November 2003 but only for 15% in May 2004 and for 26 and 5% of the NO₂⁻ added at 5 [micro]M for these two months, respectively. Decreasing the concentration of NO₃⁻ but holding NO₂⁻ at 5 [micro]M decreased the significance of anammox as a sink for NO₂⁻. The behavior of anammox was explored by use of a simple anammox-denitrification model, and the concept of a biphasic system for anammox in estuarine sediments is proposed. Overall, anammox is likely to be regulated by the availability of NO₃⁻ and NO₂⁻ and the relative size or activity of the anammox population.
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