Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Model shows long-held constant in ocean nutrient ratio may vary as ecological conditions change

13.05.2004


New research shows that what was once considered a universal constant in oceanography could actually vary in the future – depending on the ecological scenarios that affect competition for resources among microscopic marine plants, which play a role in global climate.


Microscopic image shows clumped cells of blue-green algae, a type of phytoplankton that lives in marine and freshwater environments. Phytoplankton are a rich food source for fish, and they affect global climate by using atmospheric carbon dioxide, a greenhouse gas.
Photo by Hans Paerl, Courtesy University of North Carolina’s Endeavors Magazine.



The future of these plants, called phytoplankton, is important because they exist at the base of the marine food web and represent a large source of food for fish. Also, they affect global climate by using atmospheric carbon dioxide, a greenhouse gas.

Phytoplankton depend upon nitrogen and phosphorus to grow and, ultimately, replenish the supply of these nutrients in the ocean. Since the 1930s, scientists have known that the average nitrogen-to-phosphorus (N:P) nutrient ratio of phytoplankton closely mirrors the N:P ratio in the ocean – 15:1 for the plants and 16:1 for the water. Scientists accepted this as a constant called the Redfield ratio, named after the late Harvard University scientist Alfred Redfield.


But researchers at the Georgia Institute of Technology and Princeton University designed a mathematical model based on phytoplankton physiology. It shows a broad range of N:P ratios are possible depending on the conditions under which species grow and compete. This research – part of a larger biocomplexity research project led by Professor Simon A. Levin at Princeton -- is published in the May 13 edition of the journal Nature.

"The take-home message is that this finding reinforces what some researchers have been saying lately – that N:P is not so fixed," said lead author Christopher Klausmeier, a Georgia Tech assistant professor of biology and former postdoctoral fellow at Princeton. Other authors are Elena Litchman, also of Georgia Tech, and Tanguy Daufresne and Levin of Princeton.

"This shows the range of ratios within which we could expect the ocean to change in the future," Klausmeier said. "Right now we have 16:1, but 500 years from now, if we have a different mix of growth conditions, then it might change the overall N:P needs of the phytoplankton community and the ocean."

Under two extreme conditions – one with few resources because of increased competition and the other with abundant nutrients – researchers determined the optimal strategies that phytoplankton use to allocate the cellular machinery – namely ribosomes and chloroplasts -- for nutrient uptake. Ribosomes assemble two proteins that take up nitrogen and phosphorus. Chloroplasts gather energy from the sun.

"When competing to the very end, then the optimal strategy has a lot of resource acquisition machinery, but not much assembly machinery," Klausmeier explained. "In that case, there aren’t many ribosomes, and therefore not much phosphorus. So if you have a small amount of phosphorus, you have a high N:P ratio. This strategy is best for competition to equilibrium.

"In the other scenario, where nutrients are very available, you have a lot of ribosomes. Then you have a lot of phosphorus and therefore, a low N:P ratio. This is optimal under exponential growth conditions," Klausmeier added.

Given these optimal strategies, researchers were able to determine the N:P needs of species competing at the extremes. "These two scenarios set the endpoints of what happens in reality," Klausmeier explained. "In the real world, it’s a mix of conditions."

From a literature review earlier in the study, they found that N:P ratios among different species vary from 7:1 to 43:1 – with one oddity requiring a 133:1 ratio. Results from modeling the optimal strategies mirror this range of ratios, Klausmeier said, in contrast with the long-accepted constant ratio of N:P in the ocean.

"The 16:1 Redfield ratio has been used too dogmatically by some scientists," Klausmeier said. "It has been treated as an optimum ratio, but that’s not what Redfield intended. He has been misunderstood and oversimplified. This ratio is an average that is subject to change."

As is the case in many other ecological studies, researchers in this study had to confront the natural variability found in nature.

"This is a very ecological story," Klausmeier noted. "One thing that frustrates ecology and makes it tough is that there’s a lot of natural variability. We want to explain the variability, not just the average number. So this problem turned out to be more complicated because of the variability."

Klausmeier’s findings have broader implications, as well, because of the roles phytoplankton play in the ocean ecosystem and across the globe.

"Phytoplankton do half of the planet’s primary production," Klausmeier explained. "They capture energy from the sun and have a big role in biogeochemical cycles -- how elements cycle through the biosphere. Phytoplankton have a main role in the carbon cycle. They need carbon dioxide to grow, so they suck it out of the atmosphere, controlling its presence there. And that ties into global climate."

Klausmeier believes his study contributes to a better understanding of global biogeochemical cycles. "It’s important for us to understand global climate and how it might change in the future," he added. "And ocean life, such as phytoplankton, is a big player in climate."


###
This study was funded by grants from the National Science Foundation and the Andrew Mellon Foundation for Levin’s biocomplexity project. Biocomplexity refers to studies of ecological and evolutionary systems as a whole.

Georgia Tech Research News and Research Horizons magazine, along with high-resolution JPEG images, can be found on the Web at http://www.gtresearchnews.gatech.edu.

Media Contacts:
1. Jane M. Sanders, 404-894-2214, or E-mail: jane.sanders@edi.gatech.edu.
2. John Toon, 404-894-6986, or E-mail: john.toon@edi.gatech.edu.

For technical information, contact:
1. Christopher Klausmeier, Georgia Tech, 404-385-4241 or E-mail: Christopher.klausmeier@biology.gatech.edu.
2. Simon A. Levin, Princeton University, 609-258-6880 or E-mail: slevin@eno.princeton.edu.

Jane Sanders | Georgia Tech
Further information:
http://www.gtresearchnews.gatech.edu/newsrelease/nutrient.htm

More articles from Ecology, The Environment and Conservation:

nachricht Dune ecosystem modelling
23.06.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

nachricht Understanding animal social networks can aid wildlife conservation
23.06.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>