Uncoupled Solubilization of Marine Aggregates and its Biogeochemical Significance

下沉的有机集合体的异化是调节从海洋表面到海洋深处的碳通量的一个中心问题。附着细菌在颗粒分解中的作用尚不清楚。聚集体上常见的高浓度(108-109毫升-1)缓慢生长的细菌产生强烈的胞外水解酶活性，迅速溶解颗粒结合氨基酸(0.2-2.1d周转时间)，但允许大多数水解物释放到海水中。这种“非耦合增溶”，特别是如果它普遍适用于聚集体的碳库，可能会对碳的向下流动产生深远的影响。利用收集的海洋积雪和实验室制作的14C标记的植物碎屑聚集体，研究将1)量化DOC释放(通过高温催化氧化测量)和POC周转率，以及它们如何随聚集物上的定殖率和酶活性的变化而变化。2)表征释放的DOC的分子尺寸分布(分子筛)、是否含有胶体和亚微米颗粒(通过透射电子显微镜)，以及其中一些是否不易被细菌利用(或具有较长的周转时间)；3)测试聚集体上的酶作用是否会导致C、N和P的不同增溶。这项工作将在4次巡航期间在圣巴巴拉拉霍亚附近水域和南加州海湾的几个离岸站收集的聚集体上进行。这项拟议的研究将有助于理解附着细菌在POC DOC转变中的作用，从而有助于理解海洋中的碳循环。

Dissimilation of sinking organic aggregates is a central issue in the regulation of carbon fluxes from the ocean's surface into its depths. The role of attached bacteria in particle decomposition has been unclear. High concentrations (108-109 ml-1) of slowly growing bacteria commonly found on aggregates create intense ectohydrolase activities which rapidly solubilize (0.2-2.1 d turnover time) particulate combined amino acids but allow most hydrolysate to be released into seawater. This "uncoupled solubilization", particularly if it applies generally to aggregate's carbon pool, could have profound implications for downward flux of carbon. Using SCUBA collected marine snow and laboratory-made 14C labeled phytodetritus aggregates studies will 1) quantify DOC release (measured by high temperature catalytic oxidation) and POC turnover rates and how they vary with variation in colonization and enzyme activities on aggregates. 2) characterize the released DOC in terms of molecular size distribution (with molecular sieves), whether it contains colloids and sub-micron particles (by transmission electron microscopy), and whether some of it is refractory to bacterial utilization (or has long turnover time); 3) test whether enzyme action on aggregates causes differential solubilization of C, N and P. This work will be done on aggregates collected in waters off La Jolla, Santa Barbara, and at several offshore stations in Southern California Bight during 4 cruises. The proposed study will contribute to an understanding of the role of attached bacteria in POC DOC transition and hence in carbon cycling in the ocean.