Mexican mangroves have been sequestering carbon for 5,000 years

Researchers have discovered a new reason for the protection of mangrove forests: for the past 5,000 years, they have quietly kept carbon out of the Earth’s atmosphere.

Mangroves thrive in conditions that most plants cannot tolerate, such as salty coastal waters. Some species have air-conducting vertical roots that act as tubes for underwater swimming during the tides, giving the appearance of trees floating on stilts.

A research team led by the University of California, Riverside and the University of California, San Diego set out to understand how marine mangroves off the coast of La Paz, Mexico, take in and release elements like nitrogen and carbon, processes called biogeochemical cycles.

Since these processes are largely controlled by microbes, the team also wanted to know what bacteria and fungi thrive there.

The team expected the carbon to be found in a layer of peat beneath the forest, but they didn’t expect the carbon to be 5,000 years old. This result, along with a description of the microbes they discovered, has now been published in a journal Marine Ecology Progress.

“The special thing about these mangrove spots is not that they are the fastest carbon storagebut they stored carbon for so long,” said Emma Aronson, a UCR environmental microbiologist and senior co-author of the study. “It’s an order of magnitude more carbon storage than most other ecosystems in the region.”

The peat beneath the mangroves is a combination of submerged sediments and partially decomposed organic substances. In some areas sampled for this study, the peat layer extended approximately 10 feet below the coastal water line.

Little oxygen reaches the deepest layer of peat, which is probably why the team didn’t find the fungi living there; fungi are commonly found in almost every environment on Earth. However, oxygen is essential for most fungi that specialize in breaking down carbon compounds. The team may explore the absence of fungi further in future studies of mangrove peat.

More than 1,100 species of bacteria live under the mangroves, which consume and secrete various chemical elements. Many of them function in extreme conditions with little or no oxygen. However, these bacteria are not efficient at breaking down carbon.

The deeper you go into peat soils, the fewer microorganisms you will find. Not much can break down the carbon down there, either peat by itself, for that matter,” said Mia Maltz, a microbial ecologist and author of the UCR study. “Because it’s been around for so long, it’s not easy to make more of it or replicate the microbial communities in it.”

There are other ecosystems on Earth that are known to have similar or even older carbon. Arctic or Antarctic permafrost, where the ice has not yet melted, allowing gases to be released, are examples. Potentially, another mangrove forests too. Now the researchers are conducting reconnaissance mangroves research sites in Hawaii, Florida, and the Yucatan Peninsula in Mexico.

“These places protect the carbon that’s been there for millennia. If they’re disturbed, it’s going to cause carbon emissions that we won’t be able to recover from anytime soon,” said Matthew Costa, a coastal ecologist at the University of California, San Diego and first author of the paper. .

Carbon dioxide increases greenhouse effect which causes the planet to heat up. Costa believes that one way to prevent this problem from getting worse is to leave the mangroves alone.

“If we allow these forests to continue to function, they can conserve carbon they’re gone from our atmosphere, essentially forever,” Costa said. “These mangroves play an important role in mitigating the effects of climate change.”