Uptake of Other Monomers and LMW Compounds Organic Acids

Other compounds that we should consider are those derived from ligno-cellulose. Production of LMW components during oxidation of lignin, a biopolymer found only in terrestrial plants, may be quite high in fresh-waters where the input of ligno-cellulose and other allochthonous DOM is substantial (see Chapter 2). But we know little about LMW byproducts from ligno-cellulose degradation (Benner and Hodson, 1985 Moran and Hodson, 1989). 

A focus on compounds found only in cellular macromolecules would overlook labile LMW compounds produced by photochemical reactions. Although many organic compounds produced by photochemistry can also be produced by biotic processes, the contribution of photochemically-derived organic compounds to the DOM flux may be much larger than indicated by the occurrence of these compounds in cellular macromolecules or metabolic processes. Technically, most organic compounds produced by photochemical 

TABLE IV Summary of Studies Comparing Uptake of Organic Acids to Bacterial Production 

Compound Location Percentage of Bacterial Production Comments Reference 

Pyruvate East US coast and Sargasso 2-4 Bacterial production estimated indirectly Kieber et al. (1989) 

---