Lignocellulose is a major component of intertidal vascular plants and resulting detritus. It is a quantitatively important, although highly refractory, store of organic matter in coastal wetland environments such as salt marshes and mangrove swamps. As such, it represents a major source of carbon and energy to marine food webs, although microbially mediated transformations to particulate and dissolved degradation products or microbial biomass are required before the carbon from this abundant organic polymer can be utilized by metazoans. As lignocellulose is degraded by natural marine microbial populations, a significant fraction (as high as 20-50%) of the total degradation products is released into the bulk pool of dissolved organic carbon (DOC). Importantly, up to half of this lignocellulose-derived DOC (LC-DOC) fits the operational definition of "humic" material. Recent geochemical studies have shown that humic material originating in vascular plant-dominated aquatic systems is compositionally distinct from humics originating in plankton-dominated pelagic systems. Humic material has traditionally been considered to be highly recalcitrant to microbial transformation and thus, implicitly, not to be a significant carbon and/or energy source fueling bacterioplankton secondary production. This assumption has not yet been directly challenged experimentally in marine ecosystems, although there is evidence that bacterioplankton production at the expense of the humic component of DOC can be trophodynamically important in some systems, and that availability may be related to the source (and chemical composition) of the humic substances. This project involves field and laboratory studies to improve our understanding of the formation of dissolved humic substances from vascular plant lignocelluloses and determine the importance of LC-derived and natural marine humics in the support of bacterioplankton production.
