Production of oceanic nitrous oxide by ammonia-oxidizing archaea

[摘要] The recent finding that microbial ammonia oxidation in the ocean isperformed by archaea to a greater extent than by bacteria has drasticallychanged the view on oceanic nitrification. The numerical dominance ofarchaeal ammonia-oxidizers (AOA) over their bacterial counterparts (AOB) inlarge parts of the ocean leads to the hypothesis that AOA rather than AOBcould be the key organisms for the oceanic production of the stronggreenhouse gas nitrous oxide (N₂O) that occurs as a by-product ofnitrification. Very recently, enrichment cultures of marineammonia-oxidizing archaea have been reported to produce N₂O.

Here, we demonstrate that archaeal ammonia monooxygenase genes (amoA) weredetectable throughout the water column of the eastern tropical NorthAtlantic (ETNA) and eastern tropical South Pacific (ETSP) Oceans.Particularly in the ETNA, comparable patterns of abundance and expression ofarchaeal amoA genes and N₂O co-occurred in the oxygen minimum, whereas theabundances of bacterial amoA genes were negligible. Moreover, selectiveinhibition of archaea in seawater incubations from the ETNA decreased theN₂O production significantly. In studies with the only cultivatedmarine archaeal ammonia-oxidizer Nitrosopumilus maritimus SCM1, we provide the first direct evidencefor N₂O production in a pure culture of AOA, excluding the involvementof other microorganisms as possibly present in enrichments. N. maritimus showed highN₂O production rates under low oxygen concentrations comparable toconcentrations existing in the oxycline of the ETNA, whereas the N₂Oproduction from two AOB cultures was comparably low under similarconditions. Based on our findings, we hypothesize that the production ofN₂O in tropical ocean areas results mainly from archaeal nitrificationand will be affected by the predicted decrease in dissolved oxygen in theocean.

[学科分类] 地球化学与岩石