Effect of Temperature on Extracellular Polymeric Substance Production (EPS) by Diatoms

有必要确定海洋中有机物的命运，以了解海洋食物网，生物地球化学循环和气候变化。硅藻每年固定大约四分之一的全球净初级生产量，其中很大一部分作为胞外聚合物（EPS）排出。EPS通过影响聚集体的形成，对远洋生态系统产生深远影响。硅藻和其他颗粒有机碳（POC）作为聚集体迅速下沉，影响生物碳泵，而生物碳泵在海洋中的碳固存中起着关键作用。拟议的研究将测试中心假设：温度升高会影响硅藻释放EPS，EPS充当胶水，增加聚集。研究者先前的工作表明，温度升高会影响中肋骨条藻的聚集。 四个具体的假设将进行测试：H1：硅藻产生更多的EPS随着温度的升高。H2：随着温度的升高，硅藻产生更透明的外聚合物颗粒（TEP）。H3：硅藻细胞表面碳水化合物的数量或组成随温度而变化。H4：硅藻培养物和天然浮游生物的聚集随温度增加而增加。实验室实验（第1 - 2年）将使用三种模型硅藻物种进行，这些硅藻物种在连续培养中以受控的生长速率和限定的限制（氮或光）生长。培养温度将以小的增量逐步升高或降低，以确定温度变化对EPS产生、聚集和细胞内和细胞外池中碳分配的影响。在第三年将进行类似的实验，使用天然浮游生物种群从沿海网站，硅藻贡献了显着比例的生物量。更广泛的影响：拟议的研究将增加我们的生态和生理学的一个主要群体的初级生产者在地球上的理解。EPS是硅藻生物学的一个核心方面，尽管EPS生产的生理学，功能和更广泛的生态系统影响仍然未知。这项研究将确定温度，光照限制和营养限制如何影响海洋中溶解，凝胶和颗粒相之间的生产分配。测量浮游生物粘性（α）在不同条件下将是重要的模型在海洋中的聚集过程，因为α是一个重要的（和可变的）凝结模型。确定碳如何在海洋、大气和岩石圈之间循环是理解地质和人类时间尺度上气候变化的关键。这是一个重大的社会问题，因为大气中的二氧化碳浓度正在稳步上升，与上个世纪全球平均气温上升0.6摄氏度相关。该研究将解决海洋表层变暖、硅藻生态生理学和生物碳泵之间的潜在反馈。研究生将接受该项目的支持，并接受微生物生态学和生物地球化学方面的培训。来自德克萨斯A M大学校园的本科生将有机会获得海洋学研究经验。这些学生将通过开展个人研究项目成为研究的积极合作伙伴。研究结果将主要通过同行评审的出版物和科学会议上的演讲传播，学生在传播过程的各个阶段发挥积极作用。

It is necessary to determine the fate of organic matter in the ocean to understand marine food webs, biogeochemical cycles, and climate change. Diatoms fix approximately a quarter of the net global primary production each year, and a significant proportion of this production is excreted as extracellular polymeric substances (EPS). EPS have a profound impact on pelagic ecosystems by affecting the formation of aggregates. Diatoms and other particulate organic carbon (POC) sink rapidly as aggregates, affecting the biological carbon pump, which plays a pivotal role in the sequestration of carbon in the ocean. The proposed research will test the central hypothesis: Temperature increase affects diatom release of EPS, which act as a glue, increasing aggregation. Previous work by the investigator showed that increased temperatures affected the aggregation of Skeletonema costatum. Four specific hypotheses will be tested: H1: Diatoms produce more EPS with increasing temperature. H2: Diatoms produce more transparent exopolymer particles (TEP) with increasing temperature. H3: The quantity or composition of cell-surface carbohydrates in diatoms changes with temperature. H4: Aggregation of diatom cultures and natural plankton increases with temperature. Laboratory experiments (years 1 - 2) will be conducted with three model diatom species grown at controlled growth rates and defined limitation (nitrogen or light) in continuous culture. Culture temperature will be stepped up or down in small increments to determine the effect of the temperature change on EPS production, aggregation, and partitioning of carbon in intra- and extracellular pools. Similar experiments in year 3 will be carried out using natural plankton populations from a coastal site where diatoms contribute a significant proportion to the biomass.Broader Impacts: The proposed research will increase our understanding of the ecology and physiology of one of the dominant groups of primary producers on Earth. EPS are a central aspect of diatom biology, though the physiology, function and broader ecosystem impacts of EPS production remain unknown. This research will determine how temperature, light limitation, and nutrient limitation affect the partitioning of production between dissolved, gel, and particulate phases in the ocean. Measurements of plankton stickiness (alpha) under different conditions will be important to model aggregation processes in the ocean as alpha is an important (and variable) term in coagulation models. Determining how carbon is cycled between the ocean, atmosphere and lithosphere is key to understanding climate change on both geological and human time scales. This is a major societal issue as atmospheric CO2 concentrations are steadily increasing, correlating with a 0.6C rise in global average temperature during the last century. This research will address potential feedbacks between warming of the surface ocean, diatom ecophysiology and the biological carbon pump.A graduate student will be supported by this program and receive training in microbial ecology and biogeochemistry. Undergraduates from across the Texas A&M University campus will be offered an opportunity for hands on research experience in oceanography. These students will become active partners in the research by conducting individual research projects. Results from the research will primarily be disseminated through peer-reviewed publications and presentations at scientific meetings, with students playing an active role at all stages in the dissemination process.