Environmental controls on the activity of ammonia oxidizing archaea and bacteria in temperate forest soils

Background/Question/Methods

Ammonia oxidation is the rate-limiting step of nitrification, a critical process, which controls inorganic nitrogen mobility in soils.  Ammonia oxidation is performed by two major groups of chemoautotrohpic microorganisms: ammonia oxidizing bacteria (AOB) and recently discovered ammonia oxidizing archaea (AOA).  Though AOA greatly outnumber AOB in most temperate soil environments, little is known about the in situ activity of these groups.  Using quantitative polymerase chain reaction, we assessed the growth of these organisms by change in gene copy number during the course of field nitrification incubations.  Using this dynamic approach, we sought to understand whether AOA or AOB are responsible for ammonia oxidation in temperate forest soils at Coweeta LTER.  

Results/Conclusions

We have identified significant growth of AOB during the course of field incubations at all but one of our sampling sites, indicating that AOB may be responsible for a large amount of nitrification in this system despite their low abundance in Coweeta soils.  Ongoing work will determine which edaphic variables control the activity of these groups, leading to a better understanding of niche-differentiation between these phylogenetically-disparate members of the functional group of ammonia oxidizing microorganisms.