Microbes making tree methane in ghost forests are in the soils

Date:
February 2, 2022
Source:
North Carolina State University
Summary:
Researchers wanted to know if different communities of microbes
are making methane gas inside the soils or in the dead trees, which
are also known as snags. They found that although the methane gas
is generated in the soils, the trees act like filtering straws as
the gas rises through the wood.



FULL STORY ==========================================================================
A new study from North Carolina State University shows that methane, a
potent greenhouse gas, is largely generated in the soils below standing
dead trees in so-called ghost forests, or coastal forests that are being
killed off by rising sea levels.


==========================================================================
This escaping methane gas, known colloquially as ghost
forest tree "farts," is actually generated by different tiny
microorganisms. Researchers wanted to know if different communities of
microbes are making methane gas inside the soils or in the dead trees,
which are also known as snags. They found that although the methane
gas is generated in the soils, the trees act like filtering straws as
the gas rises through the wood. Microbes in the wood further chemically
alter and consume the gas as it rises.

"We're tracing where the methane is originally coming from, and
what we're finding is that it's coming from the soils, and as it
moves through the tree, it's changing as well," said Marcelo Ardo'n,
associate professor of forestry and environmental resources at North
Carolina State University. "The methane is being processed as it moves
through those snags." As a visual sign of climate change, ghost forests
are expected to become more common along the coast in the Southeast due
to rising sea levels. In a previous study, Ardo'n and colleagues found
that snags are important to calculating greenhouse gas emissions from
ghost forests, and ignoring them could discount some of the emissions
generated in a transitioning forest. In their new study, the researchers
wanted to understand the methane's source.

To answer that question, the researchers analyzed methane gas samples
from standing dead trees in ghost forests across five sites on the Albemarle-Pamlico Peninsula on the North Carolina coast. They measured concentrations of the gas inside the trees, in the soils and in the water
in the soil. They also tracked chemical signatures left by the microbes
that produce and use methane gas.

Methane is made of two elements -- hydrogen and carbon -- and each of
these elements can have a different molecular weight from other atoms of
the same type depending on the number of neutrons in their nuclei. Those variations in the elements are called isotopes, and since they're not radioactive, they're called stable isotopes. Researchers analyzed the
amounts and types of stable isotopes of each element to help them track methane.

"The stable isotope signature is like a fingerprint you can follow," said
the study's first author Melinda Martinez, a former graduate student
at NC State, and now a postdoctoral scholar at the U.S. Geological
Survey. "In our previous work, we saw that methane was coming out of the
trees. Where is it coming from? Is it coming from the soil, produced
by microbes, or within the tree itself as it decomposes?" They found
methane concentrations generally decreased the higher they got from the
ground in the dead trees. They also saw evidence of a change in ratios
between lighter and heavier isotopes in both carbon and hydrogen from
the water in the ground to the soils to the snags.

Lastly, they took samples from the trees and placed them in vials to
see if they were producing any methane when isolated in an oxygen-free environment, or if any methane was used in an oxygen-rich vial. They
found very little methane was produced or consumed in the vials.

"Only five out of 100 vial samples produced any significant results,
which provides further evidence that the methane being emitted from
standing dead trees originated in the soil," Martinez said.

The findings just address one greenhouse gas, but researchers say it's important because understanding methane fluxes are significant for understanding the environmental impact of the forest-to-ghost forest transition. Methane has a higher warming potential than carbon dioxide, researchers said.

"It's important to be able to understand how methane is moving through
the ecosystem," Martinez said. "These ghost forest regions are temporary ecosystems; they will become marshes. But even during the transient state,
we want to know how ghost forests produce and move this greenhouse gas."
The study, "Identifying Sources and Oxidation of Methane in Standing
Dead Trees in Freshwater Forested Wetlands," was published online
in Frontiers in Environmental Science on Feb. 1, 2022. In addition to
Ardo'n and Martinez, the other author was Mary J. Carmichael. The study
was funded by the National Science Foundation (DEB1713502) and by the
North Carolina Sea Grant/Space Grant Fellowship (2019).

========================================================================== Story Source: Materials provided
by North_Carolina_State_University. Original written by Laura
Oleniacz. Note: Content may be edited for style and length.


========================================================================== Journal References:
1. Melinda Martinez, Marcelo Ardo'n, Mary Jane Carmichael. Identifying
Sources and Oxidation of Methane in Standing Dead Trees in
Freshwater Forested Wetlands. Frontiers in Environmental Science,
2022; 9 DOI: 10.3389/fenvs.2021.737379
2. Melinda Martinez, Marcelo Ardo'n. Drivers of greenhouse gas
emissions
from standing dead trees in ghost forests. Biogeochemistry, 2021;
154 (3): 471 DOI: 10.1007/s10533-021-00797-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220202124322.htm

--- up 8 weeks, 4 days, 7 hours, 13 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)