Microbial nitrification, denitrification and respiration in the leached cinnamon soil of the upper basin of Miyun Reservoir

Nitrification, denitrification and respiration are major processes affecting soil greenhouse gases (i.e., CO2 and N2O) emissions and soil nitrogen availability1–6. It has been proven that CO2 emission from microbial respiration in soils was in excess of any other terrestrial -atmospheric carbon transactions, which is thus considered as the primary natural source for CO2 emission7,8. The increase of soil CO2 emission had the potential of promoting atmospheric CO2 levels, which in turn would aggravate global warming 9–13. Recently, a series of studies have addressed microbial respiration under multiple tillage methods, hydraulic properties and vegetation covers8,14,15. A few researchers also found that microbial respiration was strongly influenced by soil nitrogen availability through multiple complex approaches, with both inhibition and promotion effects being observed16–19. Compared to CO2, nitrous oxide (N2O) was identified to be much more destructive to environment. It is well known that N2O has 265 times greater global warming potential than that of CO2, and may lead to ozone depletion in the stratosphere20. Researchers revealed that agricultural soil was also the major source of N2O emission, and almost all the processes that involving N2O production were biotic21,22. From a theoretical point of view, microbial nitri-fication and denitrification in soils, especially the simultaneous nitrification-denitrification processes under low oxygen conditions, were widely acknowledged to be the most crucial mechanism that was related to a significant amount of N2O emission22–24. Considerable studies have been launched to determine the factors that are influenc-ing soil N2O emission during nitrification and denitrification processes, including soil temperature, moisture,
carbon source, COD/NH+4 ratio and nitrite accumulation25–27.