Microbial Food Webs in Marine Sediments: Spatial Motives Link Bacterivory and Biogeochemistry

*9618135爱泼斯坦这个项目解决了沉积物微食性动物和具有特殊生物地球化学重要性的细菌之间的营养关系。这表明，原生和微型后生动物食草动物平衡了沉积物中化学和光营养物质的产生，从而成为硫、氮和碳(可能还有锰和铁)还原和氧化形式的动力学中的重要参与者。这一想法得到了先前工作、试点数据和文献信息的支持。所有这些数据都表明了以下想法。1.主要的沉积物微生物(鞭毛虫、纤毛虫、线虫等)集中在特定的沉淀层中，位于氧化/缺氧界面及其下方。2.大多数硫化物、氨和甲烷氧化的化学富营养化细菌以及厌氧光合作用细菌正是集中在这一沉积层中。3.在这一特殊的层中，表现出对细菌的放牧压力增加，微型食草动物似乎每天清除高达50%的细菌常备。基于上述证据，提出了以下假设。原生后生动物和微型后生动物放牧控制了特定沉积层中的细菌动态，这些沉积层位于氧气/缺氧界面及其正下方。这一假设将通过比较沉积物鞭毛虫、纤毛虫、线虫和其他微食性动物的细菌率与已确定的沉淀层中的细菌现存量和细菌产量来验证。这将通过古典、现代和新颖的方法相结合来实现。季节性将通过在两个不同的季节进行实验来检验，这两个季节之前被证明在微生物食物网结构中相互对比。在每个季节的时间点，实验将考虑到放牧活动的每日动态和潜在食菌者的垂直迁徙。在之前的NSF支持下，这里使用的许多关键技术都得到了实质性的改进，并收集了支持证据。模式社区(优良的潮间带沙，波斯顿港)已经研究了几年，特别适合于计划中的研究。这项工作是首次将空间动机引入沉积物微生物食物网的研究。这项研究的目标是那些在沉积物生物地球化学、营养循环和沉积物-水交换中特别重要的功能类型的细菌。因此，研究这些细菌动态的机制的意义超出了其对详细描述海底微生物食物网络结构的内在价值，并且在更大的生态背景下具有重要意义。***

*** 9618135 Epstein This project addresses trophic relations between sediment micrograzers and bacteria of particular biogeochemical importance. It is suggested that proto- and micrometazoan grazers balance production of sediment chemo- and photolithotrophs and thus become important players in the dynamics of reduced and oxidized forms of sulfur, nitrogen, and carbon, and possibly Mn and Fe. This idea is supported by the results of previously work, pilot data, and literature information. All these data suggest the following ideas. 1. Major sediment microbacterivores (flagellates, ciliates, nematodes, and others) are concentrated in a specific sediment layer, at and immediately below oxic/anoxic interface. 2. It is exactly in this sediment layer that most sulfide, ammonium, and methane oxidizing chemolithotrophs, as well as anaerobic photosynthesizers, are known to concentrate. 3. In this particular layer, which exhibits increased grazing pressure over bacteria, micrograzers appear to remove daily up to 50% of bacterial standing stock. Based on the above evidence, the following hypothesis is advanced. Proto- and micrometazoan grazing controls bacterial dynamics in a specific sediment layer at and immediately below the oxic/anoxic interface. The hypothesis will be tested by comparing the rates of bacterivory by sediment flagellates, ciliates, nematodes, and other micrograzers, with bacterial standing stock and bacterial production in the identified sediment layer. This will be done by a combination of classical, modern, and novel approaches. Seasonality will be examined by conducting the experiments in two different seasons, which were previously shown to contrast with each other in the microbial food web structure. At each seasonal time point, experiments will account for daily dynamics in grazing activity and vertical migrations of prospective bacterivores. Many key techniques to b e used here have been substantially improved, and supporting evidence collected, under prior NSF support. The model community (fine intertidal sands, Boston Harbor) has been under study for several years and is uniquely suited for the planned research. This work is one of the first to introduce spatial motives into studies of sediment microbial food webs. The target of this research are those functional types of bacteria that are particularly important in sediment biogeochemistry, nutrient recycling, and sediment-water exchange. The significance of studying mechanisms governing these bacteria dynamics goes therefore beyond its intrinsic value for detailing benthic microbial food web structure, and is important in a much larger ecological context. ***