Sweet spots in the sea: Mountains of sugar under seagrass meadows

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Lush meadows of the seagrass Posidonia oceanica in the Mediterranean. Scientists at the Max Planck Institute of Marine Microbiology predict that their findings are relevant for many marine environments with plants, including other seagrass species, mangroves and saltmarshes. Credit: HYDRA Marine Sciences GmbH

Seagrasses play an important role in the climate. They are one of the most efficient sinks of carbon dioxide on Earth. A team of scientists from the Max Planck Institute for Marine Microbiology now reports that seagrasses release large amounts of sugar, largely in the form of sucrose, into their soils—worldwide more than 1 million tons of sucrose, enough for 32 billion cans of coke. Such high concentrations of sugar are surprising. Normally, microorganisms quickly consume any free sugars in their environment. The scientists found that seagrasses excrete phenolic compounds, and these deter most microorganisms from degrading the sucrose. This ensures that the sucrose remains buried underneath the meadows and cannot be converted into CO2 and returned to the ocean and atmosphere. They now describe their discovery in the journal Nature Ecology & Evolution.

Seagrasses form lush green meadows in many around the world. These are one of the most efficient global sinks of dioxide on Earth: One square kilometer of seagrass stores almost twice as much carbon as forests on land, and can do so 35 times as fast. Now scientists from the Max Planck Institute for Marine Microbiology in Bremen, Germany, have discovered that seagrasses release massive amounts of sugar into their soils, the so-called . Sugar concentrations underneath the seagrass were at least 80 times higher than previously measured in marine environments.

“To put this into perspective: We estimate that worldwide there are between 0.6 and 1.3 million tons of sugar, mainly in the form of sucrose, in the seagrass rhizosphere,” explains Manuel Liebeke, head of the Research Group Metabolic Interactions at the Max Planck Institute for Marine Microbiology. “That is roughly comparable to the amount of sugar in 32 billion cans of Coke.”

Polyphenols keep microbes from eating the sugar

Microbes love sugar. It is easy to digest and full of energy. So why isn’t the sucrose consumed by the large community of microorganisms in the seagrass rhizosphere? “We spent a long time trying to figure this out,” says first author Maggie Sogin, who led the research off the Italian island of Elba and at the Max Planck Institute for Marine Microbiology. “What we realized is that seagrass, like many other plants, release to their sediments. Red wine, coffee and fruits are full of phenolics, and many people take them as health supplements. What is less well known is that phenolics are antimicrobials and inhibit the metabolism of most microorganisms.

“In our experiments, we added phenolics isolated from seagrass to the microorganisms in the seagrass rhizosphere—and indeed, much less sucrose was consumed compared to when no phenolics were present.”

Beautiful to look at, hard to sample: Measuring metabolites like sucrose and polyphenols in seawater is difficult. The scientists from the Max Planck Institute for Marine Microbiology in Bremen had to develop a special method to deal with the large amounts of salt in seawater that make measurements of metabolites so difficult. Credit: HYDRA Marine Sciences GmbH

Some specialists thrive on sugars in the seagrass rhizosphere

Why do seagrasses produce such large amounts of sugars, and then dump them into their rhizosphere? Nicole Dubilier, Director at the Max Planck Institute for Marine Microbiology explains: “Seagrasses produce sugar during photosynthesis. Under average light conditions, these plants use most of the sugars they produce for their own metabolism and growth. But under high light conditions, for example, at midday or during the summer, the plants produce more than they can use or store. Then they release the excess sucrose into their rhizosphere. Think of it as an overflow valve.”

Intriguingly, a small set of microbial specialists are able to thrive on the sucrose despite the challenging conditions. Sogin speculates that these sucrose specialists are not only able to digest sucrose and degrade phenolics, but might provide benefits for the seagrass by producing nutrients it needs to grow, such as nitrogen. “Such beneficial relationships between plants and rhizosphere microorganisms are well known in , but we are only just beginning to understand the intimate and intricate interactions of seagrasses with microorganisms in the marine rhizosphere,” she adds.

Manuel Liebeke and Nicole Dubilier in the lab. Credit: Achim Multhaupt

Endangered and critical habitats

Seagrass meadows are among the most threatened habitats on our planet. “Looking at how much blue carbon—that is carbon captured by the world’s ocean and coastal ecosystems—is lost when seagrass communities are decimated, our research clearly shows: It is not only the seagrass itself, but also the large amounts of sucrose underneath live seagrasses that would result in a loss of stored carbon. Our calculations show that if the in the seagrass rhizosphere was degraded by microbes, at least 1.54 million tons of carbon dioxide would be released into the atmosphere worldwide,” says Liebeke. “That’s roughly equivalent to the amount of carbon dioxide emitted by 330,000 cars in a year.”

Seagrasses are rapidly declining in all oceans, and annual losses are estimated to be as high as 7% at some sites, comparable to the loss of coral reefs and tropical rainforests. Up to a third of the world’s seagrass might have been already lost. “We do not know as much about seagrass as we do about land-based habitats,” Sogin emphasizes. “Our study contributes to our understanding of one of the most critical coastal habitats on our planet, and highlights how important it is to preserve these blue carbon ecosystems.”



More information:
Maggie Sogin, Sugars dominate the seagrass rhizosphere, Nature Ecology & Evolution (2022). DOI: 10.1038/s41559-022-01740-z. www.nature.com/articles/s41559-022-01740-z

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Sweet spots in the sea: Mountains of sugar under seagrass meadows (2022, May 2)
retrieved 3 May 2022
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Hexbyte Glen Cove Fermi spots a supernova's 'fizzled' gamma-ray burst thumbnail

Hexbyte Glen Cove Fermi spots a supernova’s ‘fizzled’ gamma-ray burst

Hexbyte Glen Cove

When the core of massive star collapses, it can form a black hole. Some of the surrounding matter escapes in the form of powerful jets that rush outward at almost the speed of light in opposite directions, as illustrated here. Normally jets from collapsing stars produce gamma rays for many seconds to minutes. Astronomers think the jets from GRB 200826A were shut down quickly, producing the shortest gamma-ray burst (magenta) from a collapsing star ever seen. Credit: NASA’s Goddard Space Flight Center/Chris Smith (KBRwyle)

On Aug. 26, 2020, NASA’s Fermi Gamma-ray Space Telescope detected a pulse of high-energy radiation that had been racing toward Earth for nearly half the present age of the universe. Lasting only about a second, it turned out to be one for the record books—the shortest gamma-ray burst (GRB) caused by the death of a massive star ever seen.

GRBs are the most powerful events in the universe, detectable across billions of light-years. Astronomers classify them as long or short based on whether the event lasts for more or less than two seconds. They observe long bursts in association with the demise of massive , while short bursts have been linked to a different scenario.

“We already knew some GRBs from massive stars could register as short GRBs, but we thought this was due to instrumental limitations,” said Bin-bin Zhang at Nanjing University in China and the University of Nevada, Las Vegas. “This burst is special because it is definitely a short-duration GRB, but its other properties point to its origin from a collapsing star. Now we know dying stars can produce , too.”






Astronomers combined data from NASA’s Fermi Gamma-ray Space Telescope, other space missions, and ground-based observatories to reveal the origin of GRB 200826A, a brief but powerful burst of radiation. It’s the shortest burst known to be powered by a collapsing star – and almost didn’t happen at all. Credit: NASA’s Goddard Space Flight Center

Named GRB 200826A, after the date it occurred, the burst is the subject of two papers published in Nature Astronomy on Monday, July 26. The first, led by Zhang, explores the gamma-ray data. The second, led by Tomás Ahumada, a doctoral student at the University of Maryland, College Park and NASA’s Goddard Space Flight Center in Greenbelt, Maryland, describes the GRB’s fading multiwavelength afterglow and the emerging light of the supernova explosion that followed.

“We think this event was effectively a fizzle, one that was close to not happening at all,” Ahumada said. “Even so, the burst emitted 14 million times the energy released by the entire Milky Way galaxy over the same amount of time, making it one of the most energetic short-duration GRBs ever seen.”

When a star much more massive than the Sun runs out of fuel, its core suddenly collapses and forms a black hole. As matter swirls toward the black hole, some of it escapes in the form of two powerful jets that rush outward at almost the speed of light in opposite directions. Astronomers only detect a GRB when one of these jets happens to point almost directly toward Earth.

Each jet drills through the star, producing a pulse of gamma rays—the highest-energy form of light—that can last up to minutes. Following the burst, the disrupted star then rapidly expands as a supernova.

Discovery image of the fading afterglow (center) of GRB 200826A. Credit: ZTF and T. Ahumada et al., 2021

Short GRBs, on the other hand, form when pairs of compact objects—such as neutron stars, which also form during stellar collapse—spiral inward over billions of years and collide. Fermi observations recently helped show that, in nearby galaxies, giant flares from isolated, supermagnetized neutron stars also masquerade as short GRBs.

GRB 200826A was a sharp blast of high-energy emission lasting just 0.65 second. After traveling for eons through the expanding universe, the signal had stretched out to about one second long when it was detected by Fermi’s Gamma-ray Burst Monitor. The event also appeared in instruments aboard NASA’s Wind mission, which orbits a point between Earth and the Sun located about 930,000 miles (1.5 million kilometers) away, and Mars Odyssey, which has been orbiting the Red Planet since 2001. ESA’s (the European Space Agency’s) INTEGRAL satellite observed the blast as well.

All of these missions participate in a GRB-locating system called the InterPlanetary Network (IPN), for which the Fermi project provides all U.S. funding. Because the burst reaches each detector at slightly different times, any pair of them can be used to help narrow down where in the sky it occurred. About 17 hours after the GRB, the IPN narrowed its location to a relatively small patch of the sky in the constellation Andromeda.

Using the National Science Foundation-funded Zwicky Transient Facility (ZTF) at Palomar Observatory, the team scanned the sky for changes in visible light that could be linked to the GRB’s fading afterglow.

“Conducting this search is akin to trying to find a needle in a haystack, but the IPN helps shrink the haystack,” said Shreya Anand, a graduate student at Caltech and a co-author on the afterglow paper. “Out of more than 28,000 ZTF alerts the first night, only one met all of our search criteria and also appeared within the sky region defined by the IPN.”

Within a day of the burst, NASA’s Neil Gehrels Swift Observatory discovered fading X-ray emission from this same location. A couple of days later, variable radio emission was detected by the National Radio Astronomy Observatory’s Karl Jansky Very Large Array in New Mexico. The team then began observing the afterglow with a variety of ground-based facilities.

Observing the faint galaxy associated with the burst using the Gran Telescopio Canarias, a 10.4-meter telescope at the Roque de los Muchachos Observatory on La Palma in Spain’s Canary Islands, the team showed that its light takes 6.6 billion years to reach us. That’s 48% of the universe’s current age of 13.8 billion years.

But to prove this short burst came from a collapsing star, the researchers also needed to catch the emerging supernova.

“If the burst was caused by a collapsing star, then once the afterglow fades away it should brighten again because of the underlying supernova explosion,” said Leo Singer, a Goddard astrophysicist and Ahumada’s research advisor. “But at these distances, you need a very big and very sensitive telescope to pick out the pinpoint of light from the supernova from the background glare of its host galaxy.”

To conduct the search, Singer was granted time on the 8.1-meter Gemini North telescope in Hawaii and the use of a sensitive instrument called the Gemini Multi-Object Spectrograph. The astronomers imaged the host galaxy in red and infrared light starting 28 days after the burst, repeating the search 45 and 80 days after the event. They detected a near-infrared source—the supernova—in the first set of observations that could not be seen in later ones.

The researchers suspect that this burst was powered by jets that barely emerged from the star before they shut down, instead of the more typical case where long-lasting jets break out of the star and travel considerable distances from it. If the black hole had fired off weaker jets, or if the star was much larger when it began its collapse, there might not have been a GRB at all.

The discovery helps resolve a long-standing puzzle. While long GRBs must be coupled to supernovae, astronomers detect far greater numbers of supernovae than they do long GRBs. This discrepancy persists even after accounting for the fact that GRB jets must tip nearly into our line of sight for astronomers to detect them at all.

The researchers conclude that collapsing stars producing short GRBs must be marginal cases whose light-speed jets teeter on the brink of success or failure, a conclusion consistent with the notion that most die without producing jets and GRBs at all. More broadly, this result clearly demonstrates that a burst’s duration alone does not uniquely indicate its origin.



More information:
B.-B. Zhang et al, A peculiarly short-duration gamma-ray burst from massive star core collapse, Nature Astronomy (2021). DOI: 10.1038/s41550-021-01395-z

Tomás Ahumada et al, Discovery and confirmation of the shortest gamma-ray burst from a collapsar, Nature Astronomy (2021). DOI: 10.1038/s41550-021-01428-7

Citation:
Fermi spots a supernova’s ‘fizzled’ gamma-ray burst (2021, July 26)
retrieved 27 July 2021
from https://phys.org/news/2021-07-fermi-supernova-fizzled-gamma-ray.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

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