Dissolved humic material -- Part IV: Light-independent fuel for the aquatic food web

摘要

Dissolved organic carbon (DOC) and dissolved humic material (DHM) are sources of energy and nutrients. For instance, it well known that DHM may be utilized via co-metabolism. However, evidence is increasing that microbial utilization is not only mediated by those exoenzymes that cleave side chains, but also by enyzmes that attack the humic backbone itself, such as phenoloxidases and phenolperoxidases. Furthermore, enzymes of the transformation systems appear to be involved in the degradation of humic substances as well. In general, high molecular weight substances, freshly released from organisms, seem to be highly bioavailable and biodegradable, leaving smaller and less bioavailable molecules behind. Despite their obvious molecular heterogeneity,a quantitative structure effect relationship between DOC/DHM and microbial growth can be established in which oxygen-rich structures inhibit microbial growth while nitrogen-rich structures support it. Higher organisms and consortia are also able to utilize DOC and DHM. For instance, several reports show that autotrophic growth can be enhanced if bacteria and DHM are present in the water. Most astonishing, zooplankton meet more than 50 percent of their carbon requiremerits through consumption of detritus, in addition to the uptake of bacteria as a source of food and energy.