| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | July 18, 2014 |
| Latest Amendment Date: | September 12, 2016 |
| Award Number: | 1434914 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Henrietta Edmonds
hedmonds@nsf.gov (703)292-7427 OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2014 |
| End Date: | August 31, 2017 (Estimated) |
| Total Intended Award Amount: | $234,419.00 |
| Total Awarded Amount to Date: | $234,419.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
615 W 131ST ST NEW YORK NY US 10027-7922 (212)854-6851 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
61 Route 9W Palisades NY US 10964-8000 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
BIOLOGICAL OCEANOGRAPHY, Chemical Oceanography |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Phosphorus is a key element for life, often present in low amounts in the vast central regions of the ocean and sometimes reaching limiting concentrations for biological productivity. Microbial uptake of dissolved phosphorus is an important lever in controlling both microbial production and the fate and cycling of marine phosphorus. This project will investigate the hypothesis that in oligotrophic environments, microbial cellular turnover of phosphorus occurs more rapidly than cellular biomass turnover, leading to a significant return of phosphorus to the dissolved pool. This rapid return of phosphorus could resupply the pool of bioavailable phosphorus, impacting microbial dynamics and fueling significant recycling of phosphorus in the surface ocean. In particular, this research will use field samples to determine the rates of cellular phosphorus and biomass turnover in the dominant groups of very small algae and bacteria inhabiting the phosphorus-depleted, surface waters of the Sargasso Sea (the region of the central North Atlantic Ocean near Bermuda). The project will be co-directed by two early-career women scientists. Their educational efforts will include training of an undergraduate student assistant as well as public educational outreach to K-12 students.
A primary objective in the study of biogeochemical cycles is linking chemical fluxes to the activity of organisms. This work will make fundamental contributions to the understanding of the biogeochemical cycling of phosphorus by linking phosphorus fluxes in the surface ocean to the activity of specific groups of microbes, and providing a mechanistic framework for the factors that control these fluxes. A significant, novel product of this research will be the determination of cellular phosphorus turnover rates relative to biomass turnover rates for individual picoplankton groups in the open ocean. To build a mechanistic understanding of the processes controlling these rates, this project will also determine the variation in picoplankton allocation of phosphorus into intracellular biochemicals. Field measurements will be augmented with experiments on axenic cultures, representative of the cell-sorted groups from the Sargasso Sea, to conduct more detailed biochemical analyses. The research team will utilize a unique suite of tools to make novel measurements from environmental samples: flow cytometry and fluorescence activated cell sorting will be combined with radioisotope labeling and biochemical analyses to quantify cell-specific phosphorus fluxes and characterize the chemical speciation of these fluxes. The significance of a high ratio of cellular phosphorus turnover rate to biomass turnover rate would be two-fold: (1) the amount of phosphorus in microbial biomass would underestimate the total phosphorus demand necessary to support microbial growth, and (2) significant recycling of dissolved phosphorus may occur in the surface ocean through microbial uptake and rapid return to the dissolved pool. By measuring these rates in field samples, the team expects to answer crucial questions about the relative impact of different microbial groups on surface ocean phosphorus fluxes and the cellular dynamics that drive these fluxes.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Phosphorus is an element that is essential for all life, and is an important nutrient for the growth of the organisms that are at the base of the food chain in the ocean: marine microbes, both phytoplankton and bacteria. In many areas of the ocean, phosphorus is found at extremely low concentrations, such that the abundance and activity of microbes may be controlled by the availability of this scarce resource. Large areas of the ocean with particularly low concentrations of phosphorus include the Sargasso Sea, in the western North Atlantic ocean, and the Gulf of Mexico (away from the coasts).
In these low phosphorus marine environments, the phytoplankton community is dominated by very small cells, from the group cyanobacteria, and non-photosynthetic bacteria—even smaller than the phytoplankton—which are the most abundant microbes of all. In these area, the concentrations of dissolved inorganic phosphorus are so low that any available nutrients are taken up extremely rapidly, with the turnover rate of dissolved phosphorus (or the renewal rate of the available nutrients) as rapid as just an hour or two. In these phosphorus-depleted environments, we hypothesized that the phytoplankton and bacteria would employ different strategies for acquiring and using this scarce resource, and that these strategies may shed light on the factors controlling their abundance and activity in low-nutrient environments.
To investigate this hypothesis, we conducted field experiments in the Sargasso Sea and in the Gulf of Mexico to quantify: 1) the rate of phosphorus uptake by different microbial groups, from different sources of dissolved phosphorus, 2) how quickly the microbes recycle this phosphorus within their cells, and 3) the strategies of different microbial groups for how they use this scarce resource within their cells. We found that the small, non-photosynthetic bacteria are responsible for the majority of phosphorus uptake, both dissolved inorganic and organic forms of phosphorus, though for an individual cell the bacteria rely less heavily on organic phosphorus than the phytoplankton. Additionally, these bacteria recycle the phosphorus within their cells more rapidly than the phytoplankton, and may be responsible for helping fuel the very rapid turnover of the dissolved phosphorus pool by consuming phosphorus, transforming it in their cells, and rapidly returning it to the dissolved pool. We quantified the distribution of phosphorus within these microbial cells to see how the microbes allocate their phosphorus between critical biochemicals including lipids, which make up the membrane of cells, DNA (deoxyribonucleic acid), which encodes genetic information in cells, and polyphosphate, which is a phosphorus storage compound and may be used as an energy reserve. We found that the phosphorus-rich, non-photosynthetic bacteria allocate more of their cellular phosphorus into lipids compared to the phytoplankton, and that one type of phytoplankton allocates more of their cellular phosphorus to polyphosphate compared to the other microbial groups. In summary, we demonstrated that bacteria are playing a distinctly different, and dominant, role in phosphorus cycling compared to phytoplankton in these low nutrient environments.
During the course of this project, the two early-career scientists leading the project worked closely with two undergraduate students, providing training and mentorship in scientific research. One of the students participated in the 9-day field experiments at sea aboard the research vessel the R/V Atlantic Explorer, gaining extensive hands-on experience with ship-based research. Both students presented the results of their research at a national conference, and one of them is leading the preparation of a paper for publication in a peer-reviewed scientific journal. To reach a younger, broader audience, we also created a workshop for middle school students. Working with the non-profit writing workshop 826NYC, over the course of four evenings, a group of middle school students explored the world of marine microbes and created five unique board games based on the marine microbial plots.
Last Modified: 09/29/2017
Modified by: Solange Duhamel
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