Nitrogen (N) in inorganic form is the main source for plant and microbial growth. Thus, gross nitrogen mineralization, a microbial process converting organic nitrogen to inorganic nitrogen, is pivotal for plant productivity. As forests are the largest terrestrial ecosystems on Earth, it is important to figure out the variation in gross nitrogen mineralization of forest soils at a large scale and the influencing factors. 

In view of this, in a recently published study on Applied Soil Ecology, researchers led by Prof. WANG Peng from the Institute of Applied Ecology of the Chinese Academy of Sciences established a 3,800-km forest transect in eastern China, along which they collected 100 soil samples, and investigated potential gross nitrogen mineralization using the N-isotope labelling approach and microbial respiration using an improved dynamic carbon dioxide trapping method. 

They found that potential gross nitrogen mineralization linearly decreased with potential evapotranspiration, and had a positively non-linear relationship with microbial respiration.

The structural equation modelling revealed that microbial substrate availability was the predominant factor influencing the variation in potential gross nitrogen mineralization along the forest transect. The extent to which potential gross nitrogen mineralization was explained by microbial respiration was comparable to that by total interactions between climate, soil and microbial variables.  

Their findings provide an important avenue for parameterizing and coupling soil N cycle models into Earth system models. 

They highlight that more attention should be paid to microbial carbon availability as indicated by microbial respiration for its role in modulating gross nitrogen mineralization of forest soils at a large scale. 

This study was supported by the National Key R & D Program of China and the National Natural Science Foundation of China. 

Non-linear relationship between potential gross nitrogen mineralization and microbial respiration. (Image by WANG Peng)