The Detritus Nitrogen Problem: New Observations and Perspectives from Organic Geochemistry

Studies of the decompositional chemistry of 5 types of estuarine macrophyte detritus were undertaken to examine relations among detrital nitrogen, protein, and other decompositional products. Protein and nitrogen contents of the detritus correlated poorly. Although the total mass of protein in all detritus decreased after 150 d of aging, there was a net increase in the mass of detrital nitrogen in some vascular plant detritus. During decomposition, detritus becomes richer in reactive phenolic and carbohydrate groups which may form condensation products with amino acids, yielding precursors to complex nitrogenous humic geopolymers. The existence of a significant positive relation between nitrogen accumulation and the production of humic substances suggests that much of the nitrogen accumulated during detritus decomposition is non-labile humic nitrogen rather than living microbial protein. The process of nitrogen enrichment often observed in detritus studies is consistent wlth the chemical behavior of nitrogen during humification. Biological availability of this humic nitrogen probably depends upon the extent to which proteinoid subunits are retained in the humic macromolecular structure.