DECOMPOSITION OF ALIPHATIC AMINES AND AMINO ACIDS IN ANOXIC SALT MARSH SEDIMENT

Abstract

Rates and pathways of decomposition of three aliphatic amines (monomethyl, dimethyl, and trimethyl amine) and three amino acids (alanine, glutamic acid, and lysine) were investigated in anoxic salt marsh sediments dominated by input from the saltmarsh cordgrass, Spartina alterniflora. Radiolabeled amines and amino acids added to sediments were either adsorbed or metabolized within 10-20 hours of addition. The proportion of added label that remained unmetabolized in the sediment solid phase was higher for amino acids than for amines. This is due to either the more reversible nature of amine than amino acid adsorption, or to a higher microbial incorporation to respiration ratio for the amines. Remineralization rate constants determined from model calculations are in the order MMA =< DMA > TMA and ALA > GLU > LYS, consistent with the adsorption behavior of these compounds. Remineralization rate constants for the amino acids were 6-10 times higher than for the amines. Experiments using specific inhibitors and labeled substrates demonstrated that the decomposition of amines was mediated by methanogens, sulfate reducers, and other microbial groups, while amino acid remineralization occurred mainly through sulfate reduction. Methanogenesis was the primary pathway for consumption of TMA produced fromSpartina -amended sediments.