all of the biochemical physiology experienment were based on few strains such as Paracoccus denitrifican, but how about the contribution of these strains in natural environment? is that typical enough for a ecological question?

also I have readed the paper named "A bet-hedging strategy for denitrifying bacteria curtails their release of N2O" , same question, since there is such mechanism in denitrifying bacteria, why is the soil still a strong source of N2O emission? Is this strain can represent the majority of the population in nature?

Denitrification is typically higher in anoxic environments because facultative microbes will preferentially use oxygen as a terminal electron acceptor instead of NO3, until oxygen becomes depleted. Incomplete denitrification leads to release of N2O, as well as nitrification.

Exactly,it also appears to what Dr J.Guinnip explained. Denitrification thus, usually starts to occur during the just occurrence of anoxic condition when there are sufficient nitrate concentration and if the habitat becomes suitable by the development of high density of denitrifying bacterial community, then nitrite as well as nitrous oxides are also subjected to denitrification depending on the other environmental conditions. Hence, DO content might hinder this processes to a larger extent.

Very good question...

Denitrification is just reverse of nitrification..in case of nitrogen, oxidation processes occured in the presence of oxygen so as to convert NH4+ to NO2- and then to NO3-...

Here in each step, oxygen atom is added...

While in case of denitrification, reduction of NO3- to NO2- and then to N2O and then to N2 and so on...here oxygen atom is subtracting from each step...

Denitrification usually occurs under water logging conditions where all the macro as well as micro pores of the soil is being filled with the water, resulting in complete anoxia and some time temporary hypoxia...denitrification is carried out by anaerobic microorganisms which generally do not require oxygen or may survive well under water stagnated conditions...for their growth and respiration, they used to receive the oxygen from nitrogen compounds like NO3-, NO2 and so on...that's why oxygen is replenished by microorganisms...

That's why there is direct relationship between oxygen and denitrification...

but I think nitrogen compounds like NO3-, NO2 and so on play as electron acceptor rather than receive the oxygen from them

Dai Xiaofeng Mam..

Yes...nitrogen compounds like NO3 or NO2 plays as electron acceptor because of variation in redox potential (ability of accepting or releasing electrons via oxidation and reduction reactions).. oxygen available in these compounds are utilized by microorganisms like pseudomonas etc...

Denitrification is reduction process in which nitrate form of nitrogen can be converted into nitrous oxide, nitric oxide and elemental nitrogen. From these both nitrous oxide and elemental nitrogen can escape into atmosphere as gases. This denitrification occur in waterlogged condition thats is why we should apply nitrate containing fertilizers at oxidized zone to prevent denitrification process. In similar way nitrification is oxidation process which needs oxygen for conversion of ammonical ion into nitrate ion. That's why we should apply ammonical fertilizers at oxidized zone. (Denitrification and Nitrification depends on redox potential too. If the redox potential is less than + 250 mV then denitrification takes place and in similar way if the redox potential is > + 250 mV nitrification will occur)

In my opinion, not all denitrifiers can complete the denitrifying processes as well as use the N2O as the electron acceptors, so the oxygen plays a role in the reducing process, like influencing the microbiology that can use it as electron acceptors as well as the N2O formation, hope this might give some insights into your question.