Microbial utilization resulting in early diagenesis of salt-marsh humic acids

Abstract

We have shown earlier that fresh and dead tissues of Spartina alterniflora, a plant species dominating Atlantic and Gulf coast salt-marshes, contain humic substances that may be released into sea water and sediment and that resemble sedimentary humic acids. In this study we found that the salt-marsh sediment-related microflora is capable of employing these humic substances under aerobic or semi-anaerobic conditions both as a supplemental source of nutrients and as the sole sources of carbon and nitrogen. Depending on cultivation conditions and type of humic substances, between 27 and 100% of the added humic acids were used. Humic acids recovered from aerobic cultures exhibited elemental and structural changes that are characteristic of diagenetic transformations of sedimentary humic substances, i.e. increase in carbon content, C:H and C:N ratios, optical density and infra-red absorption typical for aromatics. A decrease was found in oxygen content and infra-red absorption associated with proteinaceous and carbohydrate-like components of these substances. Under semi-anaerobic conditions different changes in elemental and structural characteristics of humic acids were observed.