Dead or alive: Seagrasses continue to release methane after their die-
off
Methane is formed and released from seagrass meadows, even decades after
the plants died off.

Date:
February 14, 2022
Source:
Max Planck Institute for Marine Microbiology
Summary:
Seagrass meadows play an important role in the marine carbon cycle
and our climate. On the one hand, they sequester carbon dioxide
from the atmosphere and store it underground, on the other hand,
they emit the potent greenhouse gas methane. Researchers have now
investigated what controls methane production and release from
seagrass meadows.



FULL STORY ========================================================================== Seagrasses cover shallow coastal regions of temperate and tropical seas worldwide. Seagrass meadows form the basis of an essential ecosystem that
is home to numerous animals, including endangered species of sea turtles, seahorses, and fishes. They also protect the coasts from erosion and
sequester millions of tons of carbon dioxide from the atmosphere every
year. But seagrass meadows also emit greenhouse gases, especially methane, which has a much stronger effect on our climate than carbon dioxide.


========================================================================== Where does the methane come from? Sina Schorn and her colleagues from the
Max Planck Institute for Marine Microbiology and Hydra Marine Sciences
first investigated what the methane in the seagrass meadows is formed
from. Seagrasses, like many terrestrial plants, form large peat deposits
under the sediment surface. Terrestrial peats are known to release large amounts of methane from the decomposition of the organic material. Thus,
the researchers expected that the mechanisms behind methane production
are similar in seagrass meadows. However: The opposite was the case.

"Here we experienced our first surprise," explains Schorn, the lead
author of the study.

"In seagrass sediments, methane is formed solely from one class of
organic compounds," Schorn says. "These so-called methylated compounds
are produced by the seagrass plant itself. Specialized microorganisms,
the methanogenic archaea, then convert these compounds into methane." The compounds include, amongst others, betaine: a compound that helps
seagrasses cope with changes in seawater salinity. As methanogenic archaea
can use these compounds directly, methane production in seagrass meadows
is highly efficient and robust against environmental stresses.

And something else is different in seagrass meadows than on land: The
release of methane into the water column is very fast. First of all,
the plant tissue acts as a straw, helping the gas to escape from the
seabed into the water.

Because seagrasses only grow in shallow water, pelagic microorganisms
have little opportunity to consume the methane before it ends up in
the atmosphere.

Additionally, the seawater flowing through the sands on which these
seagrasses grow, quickly 'washes out' methane from the sediment.

Also dead seagrass meadows are sources of methane As part of their study,
the Bremen researchers sampled a dead seagrass meadow.

"Here we encountered another surprise," reports Jana Milucka,
senior author of the study and head of the Greenhouse Gases Research
Group at the Max Planck Institute for Marine Microbiology. "The
rates of methane production were similar to those in the intact
seagrass meadow." Obviously, methane is still formed in dead seagrass sediments. "We believe that the reason behind this continuing methane production is that methylated compounds persist in the plant tissue for
a very long time," Milucka says. They could even be detected in plant
tissue that had died more than two decades ago.



========================================================================== Methane emissions partially offset the blue carbon effect "Currently, we
are seeing a die-off of seagrass meadows worldwide which has a devastating effect on the coastal ecosystems. Our results caution that whereas upon
the death of the plant carbon dioxide from the atmosphere will no longer
be sequestered and stored in the sediment as 'blue carbon', methane may
still continue to be released," Milucka explains.

The work reinforces the importance of seagrass meadows for our climate and highlights the need to better understand and conserve these ecosystems.

Seagrass meadows are nearshore habitats, and coastal regions are most dramatically affected by anthropogenic changes. "We need to understand
how the seagrass meadow ecosystem functions in order to determine the
impact of the ongoing global change on it," Schorn emphasizes.

Next, the researchers at the Max Planck Institute for Marine Microbiology
plan to extend their measurements to other regions and other seagrass
species. They also plan to study the microorganisms involved in methane production in greater detail, as they are surprisingly diverse and
largely understudied.

Terms Methane is a chemical compound with the molecular formula CH4. It
is the simplest hydrocarbon and a potent greenhouse gas.

Methanogenesisis the formation of methane by microorganisms
calledmethanogens.

Methanogensare microorganisms (archaea) that produce methane in the
absence of oxygen.

========================================================================== Story Source: Materials provided by Max_Planck_Institute_for_Marine_Microbiology. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Sina Schorn, Soeren Ahmerkamp, Emma Bullock, Miriam Weber, Christian
Lott, Manuel Liebeke, Gaute Lavik, Marcel M. M. Kuypers, Jon
S. Graf, Jana Milucka. Diverse methylotrophic methanogenic archaea
cause high methane emissions from seagrass meadows. Proceedings of
the National Academy of Sciences, 2022; 119 (9): e2106628119 DOI:
10.1073/ pnas.2106628119 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220214154854.htm

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