Award: OCE-1332912

The activities of plant-like cells called phytoplankton in the surface ocean serve as the basis for the marine food web, and they also serve an important role in the Earth?s climate by consuming the greenhouse gas carbon dioxide through photosynthesis. Like plants, phytoplankton need resources like nitrogen and phosphorus to grow. Nitrogen and phosphorus are thought to limit the growth of phytoplankton in many ocean regions, and studying these resources, and how they are cycled, is critical to understanding phytoplankton and their crucial role in ocean food webs and carbon cycling. This project focused on the phytoplankton genus Trichodesmium, which lives in colonies with its own attached bacteria in a community called the microbiome. Trichodesmium serves a crucial role in low nitrogen ecosystems by converting nitrogen gas into forms of nitrogen that are bioavailable to other phytoplankton, a process called nitrogen fixation. Through a series of field observations and experiments that leveraged new methods we determined that Trichodesmium is able to both make and use many forms of phosphorus, and that this phosphorus is likely exchanged with the microbiome. These findings are changing our view of how phosphorus is cycled in the ocean. We took advantage of the fact that communication molecules can be produced and taken up in the microbiome, but not by Trichodesmium, to selectively change the activity of the microbiome alone and evaluate the Trichodesmium response. Using this approach, we learned for the first time that the microbiome could change the rate of Trichodesmium nitrogen fixation. This means that communication between microscopic cells in the ocean can change the activities of phytoplankton and their crucial role in marine food webs and the carbon cycle. Last Modified: 11/30/2018 Submitted by: Sonya Dyhrman