Relationships between the Chemical Composition and Bioreactivity of Dissolved Organic Matter

RELATIONSHIPS BETWEEN THE CHEMICAL COMPOSITION AND BIOREACTIVITY OF DISSOLVED ORGANIC MATTER 

Even though substrate quality (i.e., chemical composition) is widely believed to be an important factor influencing microbial utilization of DOM, there are relatively few studies relating the composition and bioavailability of DOM. Sensitive assays for the measurement of the relative activities of various extracellular enzymes can provide an indication of the chemical composition of the bioreactive components of DOM (Sinsabaugh and Findlay, 1995 Findlay et al., 1998). The enzymatic potential of bacterial populations appears to respond fairly rapidly to seasonal changes in DOM composition in the Hudson River system. These observations clearly indicate that the chemical composition of DOM influences the microbial processing of DOM. 

Sun et al. (1997) used the H C, 0 C, and N C of DOM from the Ogeechee River system to derive an empirical equation for prediction of bacterial production on DOM. These authors found that bacterial production was positively correlated with H C and N C ratios and negatively correlated with the 0 C ratio. They also indicated that aliphatic components of river DOM were the primary C source supporting bacterial growth. 

The bioreactive fraction of particulate organic matter (POM) in 13 major rivers was characterized based on hydrolyzable neutral sugar and amino acid yields (Ittekot, 1988), and the relationship between the yields of 

Several recent studies investigated the bioavailability of DOM and total hydrolyzable neutral sugars and amino acids in lake (Weiss and Simon, 1999), creek (Volk et al., 1997 Gremm and Kaplan, 1998), and marine (Amon et al., 2001) waters. The DOM in the lake and marine environments was predominantly derived from plankton, whereas the DOM in the creek was predominantly derived from soils and decaying plant litter. Although limited in number, these systems represent a diverse array of aquatic environments. Each of these studies determined the percentages of DOC that were 

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