Mexican mangroves have been capturing carbon for 5,000 years
Researchers have identified a new reason to protect mangrove forests: they have quietly kept carbon out of the earth’s atmosphere for the past 5,000 years.
Mangroves thrive in conditions that most plants cannot tolerate, such as salty coastal waters. Some species have air-conducting vertical roots that act like snorkels when the tides are high, giving the appearance of trees floating on stilts.
A research team led by the University of California (UC) Riverside and UC San Diego set out to understand how marine mangroves off La Paz, Mexico, absorb and release elements such as nitrogen and carbon, processes called biogeochemical cycles.
Since these processes are largely driven by microbes, the team also wanted to know what bacteria and fungi thrive in them.
The team expected carbon to be in the peat layer 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 identified, is now published in the journal Series on advances in marine ecology.
“What’s special about these mangrove sites is not that they’re the fastest at storing carbon, but that they’ve held on to carbon for so long,” said microbiologist Emma Aronson. environmentalist at UC Riverside and co-lead author of the study. “That’s orders of magnitude more carbon storage than most other ecosystems in the region.”
The peat underlying the mangroves is a combination of submerged sediments and partially decomposed organic matter. In some areas sampled for this study, the peat layer extended about 10 feet below the shoreline.
Little oxygen reaches the deepest peat layer, which probably explains why the team found no fungi living there; normally, fungi are found in almost every environment on Earth. However, oxygen is a requirement for most fungi that specialize in breaking down carbon compounds. The team could further explore the absence of fungi in future studies of mangrove peat.
There are over 1,100 types of bacteria living under mangroves that consume and excrete a variety of chemicals. Many of them operate in extreme environments 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 find. Not much can break down the carbon there, or peat itself, for that matter,” said Mia Maltz, UC Riverside microbial ecologist and study author. “Because it has persisted for so long, it’s not easy to make more of it or replicate the communities of microbes it contains.”
There are other ecosystems on Earth known to have similarly aged or even older carbon. Examples are arctic or antarctic permafrost, where the ice has not yet melted allowing gas to be released. Potentially other mangrove forests as well. Researchers are also exploring mangrove research sites in Hawaii, Florida and Mexico’s Yucatan Peninsula.
“These sites protect the carbon that has been there for millennia. Disturbing them would result in a carbon emission that we couldn’t fix any time soon,” said Matthew Costa, a UC San Diego coastal ecologist and the paper’s first author.
Carbon dioxide increases the greenhouse effect which causes global warming. Costa thinks one way to prevent this problem from getting worse is to not disturb the mangroves.
“If we let these forests continue to function, they can hold the carbon they have sequestered out of our atmosphere, essentially permanently,” Costa said. “These mangroves have an important role in mitigating climate change.”
– This press release originally appeared on the University of California – Riverside website