Stabilization of N‐Compounds in Soil and Organic Matter Rich Sediments: What Is the Difference?

Abstract

Mast of the organic nitro gen in soils and sediments ultirnately derives from living organisms where it is mainly present as peptides and amina acids. These biomolecules are considered to have a biologically labile chemical structure and are expected to be quickly mineralized during early stages of organic matter stabilizatioD. In spite of this, nitrogen is still found in aged soils, I~cent and even fossilized sediments. To elucidate the nature ofthis recalcitrant Ditrogen and the processes tbat are involved in its [onnatiaD, salid-state 15N nuclear magnetic resonance (NMR) spectroscopy was recently introduced into geosciences and applied to various environments differing in tbe origin of tbeir organic matter precursors as well as in chemical and pbysical conditions of tbe environment. Results obtained witb this approach indicate tbat survival of peptide-like structures is a ubiquitous phenomenon, altbougb tbe mecbanisms for their stabilization may differ in different ecological systems. However, a conspicuous change in organic nitrogen composition is observed in fossilized sediments and for organic matter fonned by vegetation tires. Cyclization and rearrangement of peptide structures result in tbe fonnation of heteroaromatic N during fossilization, which was not detected for recent sediments and soils. From this, it may be concluded tbat such compounds are only formed in environments in which abiotic transfonnation of biogenic precursors dominates over biotic degradation.

The C:N:P:S stoichiometry of soil organic matter

“…Protein is a likely major source of the nitrogen in NRSOM. It is well-known that a high proportion of the N in material isolated from soils by alkaline extraction is derived from proteins (Stevenson 1986;Schulten and Schnitzer 1998;Knicker 2004Knicker , 2011, and a significant role for proteinaceous material in the formation of stable SOM has been advanced by a number of authors (Amelung 2003;Rumpel et al 2004;Kleber et al 2007;Rillig et al 2007;Knicker 2011). Our illustrative three-component mixture of NRSOM (Fig.…”

How relevant is recalcitrance for the stabilization of organic matter in soils?

“…There is some evidence that microbially and faunally derived compounds such as murein, chitin, certain lipids, and socalled melanins accumulate in soils (Guggenberger et al, 1994;Marseille et al, 1999;Kiem and Kögel-Knabner, 2003;Knicker, 2004). Even carbohydrates and certain peptides produced by soil microorganisms seem to be more resistant to microbial degradation, since they make up a substantial part of the stable subsoil DOC (Guggenberger et al, 1994) and can persist in soils for several decades (Gleixner et al, 1999).…”

Optical characteristic of humic acids from lake sediments by excitation-emission matrix fluorescence with PARAFAC model

“…Tryptophan, which is responsible for most of the proteins and shows the maxima in the same spectral region, seems to be the most likely source of this emission (Baker and Genty 1999). The presence of C2 and C4 fluorophores is often exhibited in dissolved OM (Stedmon et al 2003), especially in HS fractions with higher nitrogen contribution (Knicker 2004;Sierra et al 2005). In the KH extracted from lobelia lakes, the relative concentration of tyrosine-like components of C2 was generally higher than the C4 components of tryptophan Kraska and Piotrowicz (2000) c CQ = 4C/(4C + H-3N-2O)-internal oxidation factor according to Kumada (1987) derivatives.…”