Resistant N as a Component of Soil Organic Matter in Ecosystems.

Nitrogen is involved in the stability of organic matter complexes in soil.  Nitrogen is required by soil organisms for producing N-containing compounds such as enzymes and nucleic acids.  Following release or microbial death these compounds are rapidly decomposed. However, soil organic matter (SOM) requires N for some of the complex interactions such as those with minerals that result in resistant compounds. Research has demonstrated that excess N inhibits the enzymes that degrade lignin and aromatics. As we are currently seeing great increases in N as a result of anthropogenic N additions there is great need to understand the role of N in C storage.  To date the amount of N associated with rSON pools and its role in lability vs. recalcitrance has not been adequately addressed.  The amount of C in rSON compared to N (RC/RN ratio) can be quite high in the surface but those relationships change as we move deeper in soils where the older rSON exists.  Our research investigates the N content of resistant materials across the profile for native and afforested soils in MI. The amount of resistant C and N was evaluated after soils were refluxed with 6 M hydrochloric acid for 16 hours and the composition evaluated using pyrolysis –molecular beam, mass spectrometry. Across the soils sampled N increases as a component of SOM compared to C as one moved down the profile with a C:N ratio decreasing from 37:1 in the A horizon of the afforested soils to 5:1 in the C horizon.  Comparisons across land use types as related to total and resistant N should provide insight to the amount of N that is stabilized and its value as a predictor of SOM stability.