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

要了解海洋食物网、生物地球化学循环和气候变化，有必要确定海洋中有机物的命运。硅藻每年固定全球净初级生产量的大约四分之一，其中很大一部分被排泄为胞外聚合物(EPS)。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)以聚集体的形式迅速下沉，影响生物碳泵，生物碳泵在海洋碳的固定中起着关键作用。这项拟议的研究将检验中心假设：温度升高影响EPS的硅藻释放，硅藻起到粘合剂的作用，增加聚集。研究人员之前的工作表明，温度升高会影响中肋骨条藻的聚集。将检验四个具体的假设：H1：随着温度的升高，硅藻产生更多的EPS。H2：随着温度的升高，硅藻产生更透明的胞外聚合物颗粒(TEP)。H3：硅藻中细胞表面碳水化合物的数量或组成随温度变化。H4：硅藻培养物和天然浮游生物的聚集度随着温度的升高而增加。实验室实验(1-2年)将用三种模式硅藻进行，这些硅藻在连续培养中以受控的生长速度和确定的限制(氮或光)生长。培养温度将以小幅度提高或降低，以确定温度变化对胞内和胞外池中EPS的产生、聚集和分配的影响。类似的实验将在第三年进行，使用的是沿海地区的自然浮游生物种群，那里的硅藻对生物量有很大的贡献。广泛的影响：拟议的研究将增加我们对地球上主要初级生产者之一的生态学和生理学的理解。EPS是硅藻生物学的一个中心方面，尽管EPS生产的生理、功能和更广泛的生态系统影响尚不清楚。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。不同条件下浮游生物粘性(α)的测量对于模拟海洋中的聚集过程将是重要的，因为α是凝聚模型中的一个重要(和可变的)项。确定碳在海洋、大气和岩石圈之间的循环方式，是在地质和人类时间尺度上理解气候变化的关键。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，这与上个世纪全球平均气温上升了0.6摄氏度有关。这项研究将解决表层海洋变暖、硅藻生态生理学和生物碳泵之间的潜在反馈。一名研究生将得到该计划的支持，并接受微生物生态学和生物地球化学方面的培训。来自德克萨斯农工大学校园的本科生将有机会亲身体验海洋学研究。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议的出版物和在科学会议上的陈述进行传播，学生在传播过程的所有阶段都将发挥积极作用。

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.