Illustration of the study. Credit: Oregon State University
Oregon State University microbiology researchers have provided new insight into the mechanism of carbon cycling in oceans. They used a novel approach for tracking which microbes consume different types of organic carbon from common phytoplankton species.
Ryan Mueller, an associate professor at OSU's Department of Microbiology, and the lead of the research, stated that the research is an important step in forecasting how much carbon dioxide will be released into the atmosphere and how much will remain in the oceans as greenhouse gas carbon dioxide.
Today's findings were published in Proceedings of the National Academy of Sciences.
"Our research has shown that different species of microbes inhabit the ocean. They are very specific and predictable in what food sources they prefer to consume," stated Brandon Kieft (a recent Oregon State Ph.D. grad) who is currently a postdoctoral researcher at University of British Columbia. "As the oceanic environment continues to change at a rapid rate, the availability for food sources for microbes may also change. This will ultimately favor certain types of microbes over others."
Phytoplankton is a microscopic organism at the bottom of the ocean's food chains and an important component of a vital biological carbon pump. They float in the upper ocean where sunlight can reach them easily.
Because they make their own food, the tiny autotrophic plants have a significant effect on carbon dioxide levels in the atmosphere. They absorb it during photosynthesis. It is a natural sink, and one of the main ways that CO 2, the most prevalent greenhouse gas, is removed from the atmosphere. Since the dawn of industrialization, atmospheric carbon dioxide has increased by 40%, which contributes heavily to the planet's warming.
Mueller stated that Mueller is currently studying the heterotrophic microbes that consume organic material produced by primary producers, the Microbial phytoplankton. Both groups are microbes. The former consume organic carbon as food, while the latter 'fixes' their organic carbon. Our work is primarily focused upon understanding how consumers interact with microbes.
The ocean's surface stores almost as much carbon dioxide as the atmosphere. The ocean pulls in atmospheric CO2. Phytoplankton converts it into sugars and other compounds that can be used for energy.
Fixed carbon is what makes up the diet for heterotrophic microbes as well as higher organisms in the marine food web, such as fish and mammal. These organisms eventually convert the carbon back into atmospheric CO 2 via respiration or add to the carbon stock at bottom of the ocean after they die.
The main method by which fixed dissolved organic carbon from phytoplankton can be returned to the atmosphere in the form of CO2 is through the collective respiratory activity among heterotrophic microbe consumers
Mueller, Kieft, and their collaborators at the Oak Ridge, Lawrence Livermore national labs and the universities in Tennessee, Washington, and Oklahoma used stable-isotope labeling for carbon tracking as it made its way to the organic matter produced and consumed by the phytoplankton.
These isotopes were used by the scientists to determine which organisms were consuming diatoms and which cyanobacteria. Cyanobacteria are two types of phytoplankton which together produce most of the ocean's carbon fixed carbon. Researchers could also determine when consumption was occurring. For example, sometimes phytoplankton cells would produce substances called lysates in their death phase and exudates in their growth phase.
Kieft stated that "our findings have important implications for understanding marine microbes as well as photosynthetic alga function together to influence global carbon cycling" and how the oceanic food web might respond to environmental change. This will allow us to predict how much carbon we will see in the atmosphere, and how much we will find in marine sediments over many centuries.
Learn more Fishes produce approximately 1.65 billion tonnes of carbon each year through their feces, and other matter.
More information: Phytoplankton exudates support distinct microbial consortia, Proceedings of the National Academy of Sciences (2021). www.pnas.org/content/118/41/e2101178118 Journal information: Proceedings of the National Academy of Sciences Phytoplankton exudates and lysates support distinct microbial consortia with specialized metabolic and ecophysiological traits,(2021). DOI: 10.1073/pnas.2101178118