SGER: Vertical Migration in Trichodesmium as a Mechanism for Phosphorus Acquisition

固氮原核生物Trichodesmium是一种在所有温暖海洋中广泛分布的蓝藻，是海洋浮游固氮的主要已知来源。最近的研究表明，这些蓝藻的固氮水平比以往报道的要高，但这些水平仍然不足以满足海洋地点地球化学预算所需的投入。对磷的需求来支持固氮是这个问题的一个未充分研究的方面。尽管两个海洋时间序列站（BATS和HOTS）的无机磷浓度很低（纳摩尔范围），但几乎没有证据表明Trichodesmium中磷的限制。木霉菌可以利用有机磷，但浓度也很低，而且人们对木霉菌利用这些池的情况知之甚少。一个可能的磷源是迁移到营养线下的水池。一些无鞭毛的真核生物在公海中进行了垂直迁移，以获取地下氮源。众所周知，木霉可以调节浮力，并具有上升/下降速率来完成磷的迁移。然而，关于迁移是否发生，从生理和成分数据两方面都有相互矛盾的证据。该项目的目的是检查该地区木霉菌的特征，以确定是否确实发生了迁移。测定其组成和速率的方法包括呼吸速率、碳水化合物、蛋白质、多磷酸盐、CHN、颗粒P、毛状体浮力和通过PAM荧光法测定的荧光量。基于垂直迁移的真核生物模型，如果p -补给发生在深度，这些措施应该在上升和下降的细胞之间有可预测的显著差异。该项目将利用之前在澳大利亚资助的一艘Trichodesmium游轮和墨西哥湾的一艘游轮来比较不同的种群。该项目不是针对具体地点的，而是评估一种对BATS和HOTS站都有重大影响的行为。在项目结束时，将证实或驳斥木霉菌的迁移能力。这将允许直接评估垂直迁移对P获取在支持海洋固氮中的作用，并将是理解这一重要属的生态学的重大进展。

The nitrogen-fixing prokaryote Trichodesmium is a widely distributed cyanobacteria in all warm oceans and is the dominant known source of planktonic nitrogen fixation in the ocean. Recent work has documented higher levels of nitrogen fixation by these cyanobacteria than historically reported, but these levels are still inadequate to meet the inputs required by geochemical budgets at oceanic sites.The requirement for phosphorus to support nitrogen fixation is an understudied aspect of this problem. There is little evidence of phosphorus limitation in Trichodesmium despite low inorganic phosphorus concentrations (nanomolar range) at both oceanic time series stations (BATS and HOTS). Trichodesmium can use organic phosphorus, but concentrations are low as well and little is known about Trichodesmium's use of these pools.One possible phosphorus source is migration to pools beneath the nutricline. Vertical migration has been documented in several non-flagellated eukaryotes in the open sea to provide access to subsurface nitrogen sources. Trichodesmium is known to buoyancy regulate and has the ascent/descent rates to accomplish such a migration for phosphorus. However, there is contradictory evidence as to whether migration occurs from both in physiological and compositional data.The objective of this project is to examine the characteristics of Trichodesmium spp. in the field to determine if migration is actually occurring. Composition and rate measures to determine this include respiration rates, carbohydrate, protein, polyphosphate, CHN, particulate P, trichome buoyancy, and fluorescence yield via PAM fluorometry. Based on models of vertically migrating eukaryotes, these measures should vary predictably and significantly between ascending and descending cells if P-replenishment is occurring at depth. The program will utilize a Trichodesmium cruise previously funded off of Australia, and 1 cruise in the Gulf of Mexico to compare different populations. The project is not site specific, but rather is evaluating a behavior that has significant implications at both the BATS and HOTS stations.At the conclusion of the project, the migration capacity of Trichodesmium will be confirmed or refuted. This will permit direct assessment of the role of vertical migration for P acquisition in supporting nitrogen fixation in the ocean and will be a significant advance in understanding the ecology of this important genus.