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

固氮原核生物毛霉菌是一种广泛分布于所有温暖海洋的蓝藻，是海洋浮游固氮的主要已知来源。最近的工作证明，这些蓝藻的固氮水平高于历史报道，但这些水平仍然不足以满足海洋站点地球化学预算所需的输入。对磷的需求来支持固氮是这个问题研究得较少的一个方面。尽管两个海洋时间序列站(BATS和HOTS)的无机磷浓度都很低(纳摩尔范围)，但几乎没有证据表明毛霉菌中的磷是有限的。毛霉菌可以利用有机磷，但浓度也很低，对毛霉菌利用这些池的情况知之甚少。一种可能的磷来源是迁移到中线以下的池中。在公海的几种非鞭毛真核生物中记录了垂直迁徙，以提供获取地下氮源的途径。众所周知，毛霉菌具有调节浮力的作用，并具有实现磷迁移的上升/下降速率。然而，从生理和组成数据来看，是否存在迁移的证据是相互矛盾的。本项目的目的是研究毛霉的特性。以确定是否真的发生了迁移。确定这一点的组成和速率测量包括呼吸速率、碳水化合物、蛋白质、聚磷酸盐、CHN、颗粒P、毛发浮力和通过PAM荧光法获得的荧光产量。基于真核生物垂直迁移的模型，如果磷的补充发生在深处，这些测量应该在向上和向下的细胞之间有可预测的和显著的差异。该项目将利用之前在澳大利亚资助的Trichodesmium邮轮和墨西哥湾的一艘邮轮来比较不同的人口。该项目不是特定于现场的，而是在评估一种对BATS和HETS站点都有重大影响的行为。在项目结束时，毛霉菌的迁移能力将得到证实或驳斥。这将使人们能够直接评估磷的垂直迁移在支持海洋固氮方面的作用，并将在理解这一重要属的生态学方面取得重大进展。

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.