| NSF Org: |
OPP Office of Polar Programs (OPP) |
| Recipient: |
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| Initial Amendment Date: | May 31, 2017 |
| Latest Amendment Date: | May 31, 2017 |
| Award Number: | 1643345 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Karla Heidelberg
OPP Office of Polar Programs (OPP) GEO Directorate for Geosciences |
| Start Date: | October 1, 2017 |
| End Date: | September 30, 2020 (Estimated) |
| Total Intended Award Amount: | $164,510.00 |
| Total Awarded Amount to Date: | $164,510.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
2425 CAMPUS RD SINCLAIR RM 1 HONOLULU HI US 96822-2247 (808)956-7800 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1680 East-West Road Honolulu HI US 96822-2303 |
| 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): | ANT Organisms & Ecosystems |
| 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): | 47.078 |
ABSTRACT
Part 1: Nitrification is the conversion of ammonium to nitrate by a two-step process involving two different guilds of microorganisms: ammonia- and nitrite-oxidizers. The process is central to the global nitrogen cycle, affecting everything from retention of fertilizer on croplands to removal of excess nitrogen from coastal waters before it can cause blooms of harmful algae. It also produces nitrous oxide, an ozone-destroying, greenhouse gas. The energy derived from both steps of nitrification is used to convert inorganic carbon into microbial biomass. The biomass produced contributes to the overall food web production of the Southern Ocean and may be a particularly important subsidy during winter when low light levels restrict the other major source of biomass, primary production by single-celled plants. This project addresses three fundamental questions about the biology and geochemistry of polar oceans, with a focus on the process of nitrification. The first question the project will address concerns the contribution of chemoautotrophy (based on nitrification) to the overall supply of organic carbon to the food web of the Southern Ocean. Previous measurements indicate that it contributes about 9% to the Antarctic food web on an annual basis, but those measurements did not include the additional production associated with nitrite oxidation. The second question to be addressed is related to the first and concerns the coupling between the steps of the process. The third seeks to determine the significance of the contribution of other sources of nitrogen, (specifically organic nitrogen and urea released by other organisms) to nitrification because these contributions may not be assessed by standard protocols. Measurements made by others suggest that urea in particular might be as important as ammonium to nitrification in polar regions.
This project will result in training a postdoctoral researcher and provide undergraduate students opportunities to gain hand-on experience with research on microbial geochemistry. The Palmer LTER (PAL) activities have focused largely on the interaction between ocean climate and the marine food web affecting top predators. Relatively little effort has been devoted to studying processes related to the microbial geochemistry of nitrogen cycling as part of the Palmer Long Term Ecological Research (LTER) program, yet these are a major themes at other sites. This work will contribute substantially to understanding an important aspect of nitrogen cycling and bacterioplankton production in the PAL-LTER study area. The team will be working synergistically and be participating fully in the education and outreach efforts of the Palmer LTER, including making highlights of the findings available for posting to their project web site and participating in any special efforts they have in the area of outreach.
Part 2: The proposed work will quantify oxidation rates of 15N supplied as ammonium, urea and nitrite, allowing us to estimate the contribution of urea-derived N and complete nitrification (ammonia to nitrate) to chemoautotrophy and bacterioplankton production in Antarctic coastal waters. The project will compare these estimates to direct measurements of the incorporation of 14C into organic matter the dark for an independent estimate of chemoautotrophy. The team aims to collect samples spanning the water column: from surface water (~10 m), winter water (50-100 m) and circumpolar deep water (>150 m); on a cruise surveying the continental shelf and slope west of the Antarctic Peninsula in the austral summer of 2018. Other samples will be taken to measure the concentrations of nitrate, nitrite, ammonia and urea, for qPCR analysis of the abundance of relevant microorganisms, and for studies of related processes. The project will rely on collaboration with the existing Palmer LTER to ensure that ancillary data (bacterioplankton abundance and production, chlorophyll, physical and chemical variables) will be available. The synergistic activities of this project along with the LTER activities will provide a unique opportunity to assess chemoautotrophy in context of the overall ecosystem?s dynamics- including both primary and secondary production processes.
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.
Overview. Chemoautotrophic production, the conversion of inorganic carbon to organic matter driven by energy from chemical reactions rather than by light, has been proposed to augment biomass production in polar regions, particularly during winter when water column photosynthesis is reduced by low light levels. The oxidation of ammonia to nitrite and then to nitrate, a process known as nitrification, is a major chemoautotrophic process known to take place in polar water columns, yet direct comparisons of the contribution of nitrification to chemoautotrophic production in polar waters have not been made. A major goal of this project was to generate a dataset from well-characterized waters that would allow direct comparison of these two processes.
We collected samples from 3 or 4 depths chosen to represent different communities of bacterioplankton: Antarctic Surface Water (ASW, 0-35 m); Winter Water (WW, 36-174 m); Circumpolar Deep Water (CDW, 175-1000 m); and slope water (Slope, >1000 m), at stations occupied on a cruise surveying the continental shelf and slope west of the Antarctic Peninsula during the austral summer of 2018 (LMG 18-01). Concurrent sampling by the Palmer Long-Term Ecological Research program (PAL-LTER) provided ancillary data on bacterioplankton abundance and production, chlorophyll and nutrient concentrations, and physical and chemical variables that allowed us to put our measurements in a broader context. We provided them with data unique to our project (ammonium, nitrite and urea concentrations, measurements of total chemoautotrophy and nitrification rates, abundance of specific groups of microorganisms).
Nitrification rates were determined by measuring the oxidation of 15N-labeled substrates. Nitrification rates were converted to carbon equivalents using factors derived from published work with pure cultures of ammonia- and nitrite- oxidizing archaea and bacteria. We also assessed the contribution of nitrogen (N) from urea and putrescine (1,4-diamino butane, a polyamine) to chemoautotrophy via nitrification. Total chemoautotrophic production was measured as the conversion of 14C-labeled dissolved inorganic carbon into organic matter during incubations of samples in the dark. The abundance of bacteria and ammonia- and nitrite-oxidizing organisms in plankton samples was measured by quantitative amplification by PCR of specific genes in DNA extracted from plankton samples.
Significant Findings. Oxidation rates of N supplied as ammonium, nitrite or urea were negligible in ASW and were greatest in the WW and CDW water masses. Distributions of nitrifying organisms (ammonia and nitrite oxidizers) followed a similar pattern, though nitrification rates were not tightly correlated with nitrifier abundance. Mean rates (nmol L-1 d-1) across all samples (186-232 independent rate measurements) were 10.3, 3.0, 5.9 and 6.6 for ammonia, urea, nitrite and putrescine N, respectively. Mean abundance estimates over the same set of samples (31-92 independent measurements) were 7300, 1900, 660, 11 and 550 x 103 gene copies L-1 for Thaumarchaeota 16S rRNA, Water Column type B amoA, Thaumarchaeota ureC, beta-Proteobacteria amoA, and nitrite oxidizing bacteria 16S rRNA genes, respectively.
Chemoautotrophic carbon fixation rates in a subset of 42 of samples from WW, CDW and Slope water masses averaged 1.9, 1.7 and 0.05 nmol C L-1 d-1. Our calculations indicate that ammonia oxidation supported 111% and 46%, oxidation of urea N supported 22% and 39%, while nitrite oxidation supported 51% and 24 % of the chemoautotrophic production in the WW and CDW water masses, respectively.
Despite indications from previous work, oxidation rates of putrescine N were not highly correlated with ammonia oxidation rates. We had hypothesized that the oxidation of putrescine N is mediated by reactive oxygen species (ROS) produced by Thaumarchaeota during ammonia oxidation. We tested this by assessing the ability of pure cultures of two strains of Nitrospumilaceae (NOT from the Antarctic) to grow on a variety of organic nitrogen compounds. Neither isolate was able to grow on any of the polyamines tested.
However, when cultures growing on unlabeled ammonia were supplied with 15N-labeled putrescine, 15NOx was produced, suggesting that the 15N supplied as putrescine was oxidized abiotically by ROS, or that Thaumarchaeota were oxidizing 15NH4 regenerated from PUT. Direct tests of abiotic, chemical oxidation of 15N-labeled putrescine by hydrogen peroxide or peroxynitrite, two ROS species known to be produced by Thaumarchaeota during growth on ammonia, were negative. These findings suggest that our field data resulted from regeneration of 15N from putrescine by heterotrophs, or that 15N from putrescine is oxidized by another ROS species, such as superoxide.
Broader Impacts. This project resulted in training of a postdoctoral researcher and providing undergraduate students with opportunities to gain hands-on experience with research on microbial geochemistry. One of these students was an African-American woman who has gone on to graduate school in Environmental Studies and Public Policy at the University of Oregon. The LTER program, in general, is interested in ecosystem processes and how these change through space and, especially, time. Our work has contributed substantially to understanding an important aspect of nitrogen cycling and bacterioplankton production in the PAL-LTER study area.
Last Modified: 11/05/2020
Modified by: Brian N Popp
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