Marine Humic Substances: Formation Via Vascular Plant Degradation and Biological Availability

木质纤维素是潮间带维管植物及其产生的碎屑的主要成分。在沿海湿地环境，如盐沼和红树林沼泽中，它是一个数量上重要的有机物储存，尽管高度难处理。因此，它是海洋食物网碳和能量的主要来源，虽然在后生动物利用这种丰富的有机聚合物中的碳之前，需要微生物介导的转化为颗粒和溶解的降解产物或微生物生物量。随着天然海洋微生物种群对木质纤维素的降解，降解产物的很大一部分（高达20-50%）被释放到溶解有机碳（DOC）的大块池中。重要的是，多达一半的木质纤维素衍生的DOC （LC-DOC）符合“腐殖质”材料的操作定义。最近的地球化学研究表明，源自维管植物为主的水生系统的腐殖质与源自浮游生物为主的远洋系统的腐殖质在成分上是不同的。腐殖质传统上被认为对微生物转化具有高度的抗性，因此，隐含地，不是促进浮游细菌次生生产的重要碳和/或能量来源。这一假设尚未在海洋生态系统中受到实验的直接挑战，尽管有证据表明，在某些系统中，以牺牲DOC的腐殖质成分为代价的浮游细菌的产生可能对滋养动力学具有重要意义，而且可得性可能与腐殖质物质的来源（和化学成分）有关。该项目包括实地和实验室研究，以提高我们对维管植物木质纤维素中溶解腐殖质物质形成的理解，并确定lc衍生和天然海洋腐殖质在支持浮游细菌生产中的重要性。

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.