Land-use legacy effects shape microbial contribution to N2O production in three tropical forests

A Critical Review on Nitrous Oxide Production by Ammonia-Oxidizing Archaea

“…Despite the inconclusive optimal pH of archaeal functional enzymes, acidic conditions are believed to favor AOA over AOB regarding to the abundance and ammonia oxidizing activity. , Therefore, acidification could boost AOA-driven N 2 O yields subsequently. This was echoed by the findings that AOA cultivated from acidic soils had higher N 2 O production rates than those of their bacterial analogues. , …”

“…Mounting evidence have verified the involvement of ammonia-oxidizing archaea (AOA) in N 2 O production. , Multiple studies showed that AOA might compete over AOB and became the important N 2 O-producer under specific environmental conditions, particularly such as low-fertility, oxygen-limited and acidic conditions. − The mechanisms for N 2 O production by AOA are still not fully understood. By far, several AOA-driven N 2 O production pathways have been proposed as follows: (1) akin to AOB, the archaeal ammonia monooxygenase (AMO) catalyzes the aerobic oxidation of NH 3 to NH 2 OH, followed by the conversion to N 2 O by putative enzymes in AOA; ,, (2) with HNO working as the intermediate of AMO, N 2 O might be formed by an archaeal putative enzyme such as nitroxyl oxidoreductase (NXOR); , (3) by the aid of nitrite reductase (NIR), NO is produced and may serve as an electron delivery mechanism to assist the activation of AMO and the associated NH 2 OH output for N 2 O production; , (4) through putative nitrifier denitrification pathway, AOA utilize nitrite and nitric oxide as the alternative electron acceptors to produce N 2 O; − and (5) abiotic reactions, in which N 2 O is produced with one N source from NH 4 + and the other one from NO 2 – or NH 2 OH. ,,, Some of the archaeal N 2 O production pathways still need further investigation, since no conclusive homologue or substitute of the key enzymes [e.g., hydroxylamine dehydrogenase (HAO) and nitric reductase (NOR)] involved in N 2 O formation has been found. , …”

“…AOA are widespread and abundant in marine environments. , The estimated contribution of N 2 O production by AOA in marine ecosystems varied widely, accounting for 6.20–33.60% of total oceanic N 2 O production depending on specific conditions. ,, As for aerobic soil, N 2 O production was mainly associated with ammonia oxidation . AOA frequently outnumbered AOB regarding abundance and ammonia oxidizing activity in soil with low ammonia availability and relatively good ventilation conditions. ,, However, the primacy of AOA in producing N 2 O under oligotrophic conditions is not evidenced widely. Despite that insignificant AOA-originated contribution to N 2 O were reported by some researchers, high amount of archaeal N 2 O production were still validated in some studies. ,, For example, up to 40–60% of edaphic N 2 O were sourced from AOA in unfertilized soil. ,,, Also of note is that around 10% of N 2 O were driven by AOA in nitrogen amended soil, where AOB exceeded AOA regarding abundance .…”

“…AOA frequently outnumbered AOB regarding abundance and ammonia oxidizing activity in soil with low ammonia availability and relatively good ventilation conditions. ,, However, the primacy of AOA in producing N 2 O under oligotrophic conditions is not evidenced widely. Despite that insignificant AOA-originated contribution to N 2 O were reported by some researchers, high amount of archaeal N 2 O production were still validated in some studies. ,, For example, up to 40–60% of edaphic N 2 O were sourced from AOA in unfertilized soil. ,,, Also of note is that around 10% of N 2 O were driven by AOA in nitrogen amended soil, where AOB exceeded AOA regarding abundance . In terms of wastewater treatment system (WWTS), the involvement of AOA in N 2 O production by AOA is highly possible due to the wide existence of AOA .…”

“…4 AOA frequently outnumbered AOB regarding abundance and ammonia oxidizing activity in soil with low ammonia availability and relatively good ventilation conditions. 9,10,20 However, the primacy of AOA in producing N 2 O under oligotrophic conditions is not evidenced widely. Despite that insignificant AOA-originated contribution to N 2 O were reported by some researchers, 8 high amount of archaeal N 2 O production were still validated in some studies.…”