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碎屑的主要成分。在盐沼和红树林沼泽等沿海湿地环境中，它是一种数量上重要的有机物质储藏库，尽管具有很高的耐火性。因此，它是海洋食物网的主要碳和能源来源，尽管在后生动物可以利用这种丰富的有机聚合物中的碳之前，需要通过微生物将其转化为颗粒和溶解的降解产物或微生物生物量。由于木质纤维素被自然的海洋微生物群降解，总降解产物的很大一部分(高达20%-50%)被释放到大量溶解有机碳(DOC)中。重要的是，多达一半的这种木质纤维素衍生的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，起源于维管植物为主的水生系统的腐殖质在成分上不同于起源于浮游生物为主的远洋系统的腐殖质。腐殖质传统上被认为是对微生物转化的高度抵抗，因此，隐含地，不是推动浮游细菌二次生产的重要碳和/或能源。这一假设尚未在海洋生态系统中受到直接的实验挑战，尽管有证据表明，在某些系统中，以腐殖质成分DOC为代价的浮游细菌的生产在营养动力学上可能是重要的，而且有效性可能与腐殖质的来源(和化学组成)有关。该项目涉及现场和实验室研究，以提高我们对维管植物木质纤维素溶出腐殖质形成的了解，并确定LC衍生和天然海洋腐殖质在支持浮游细菌生产方面的重要性。

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.