Not Amazon, Earth also has a larger lung in the ocean but few people know it

Living on the surface of the earth, we humans often think of tropical rainforests as the green lungs of the planet . In hundreds of millions of years, the rainforest has constantly absorb large amounts of carbon dioxide (CO ₂ ) from the atmosphere and produce oxygen to support life for the animals.

To be fair, however, it turns out that the Earth is still breathing with larger lungs in the ocean, an ecosystem few of us know about: The seagrass meadows.

Seagrass field.

Seagrass is not seaweed, nor algae or coral. They are plants and used to live on land. Seagrasses belong to the group of monocotyledonous plants. They have roots, leaves, flowers, and even flowers that can be pollinated underwater.

This plant once had a common ancestor with terrestrial grasses, but about 100 million years ago, seagrasses found their way down and grew on the ocean floor. Here, they keep the tradition of photosynthesis, exchanging CO ₂ and oxygen as usual.

Each square meter of seagrass can produce 10 liters of oxygen per day through photosynthesis. And they also absorb carbon 35 times faster than rainforests. Seagrass ecosystems are among the largest carbon sinks on the planet. Despite covering only 0.1% of the sea floor, this species is storing 11% of the carbon found in the ocean floor.

Even scientists are surprised by the carbon sequestration capacity of seagrass

Seagrasses have roots, leaves, flowers, and even flowers that can be pollinated underwater.

But, what helped seagrass defeat the rainforest in its quest to purify CO ₂ for the Earth? It turns out that hidden under the seagrass meadows is still a hidden hero. Without the presence of this creature, seagrasses will wither and lose almost all of their ability to capture carbon.

In a new study in the journal Nature, scientists discovered in the roots of the seagrass Neptune (Posidonia oceanica) a bacterium called Celerinatantimonas neptuna. This bacterium turned nitrogen into a nutrient that seagrasses need for photosynthesis.

That process is called nitrogen fixation or nitrogen fixation . The bacterium C. neptuna seems to have followed the seagrasses as they migrated from the land back into the ocean about 100 million years ago. And the close friendship between these two species turned out to have helped the Earth become greener than ever.

During the migration to the seabed

We know that all terrestrial plants actually evolved from a group of green algae about 450 million years ago. As algae in the sea, they have no roots, no flowers and get nutrients through water permeation rather than from roots that penetrate the seabed.

Coming out of the water, new plants begin to equip themselves with specific reproductive and metabolic mechanisms such as roots, stems, leaves, flowers and seeds. Like algae, plants also photosynthesize, but they do not use the pigment phycobilin, but only chlorophyll and carotenoids.

Terrestrial plants are clearly a much more evolved form than marine algae. Algae may be unicellular, filamentous, and live a life floating in the ocean, but plants are not, they must be multicellular, with complex bodies and roots firmly anchored to the ground. .

But about 70-100 million years ago, there was a group of plants living around the mangrove swamps, suddenly wanting to give up the atmosphere and migrate back to the ocean floor. They colonize shallow water areas to further capture sunlight and photosynthesize.

Terrestrial plants are clearly a much more evolved form than marine algae.

Gradually, this plant species has reached a depth of 60 meters, proliferating and developing into more than 60 species of 5 different subfamilies. They cover vast areas of sea, possibly up to 4,500 square kilometers, forming fields under the shelves of all continents except Antarctica.

At this point, needless to say, you probably already know we're talking about seagrasses and their admirable migrations. But what we haven't talked about is that the success of seagrasses in re-invading the oceans is also attributed to their symbiotic species, nitrogen-fixing bacteria.

Seagrasses need protein, but where do they get it?

Proteins or nitrogenous substances are an essential ingredient for all life processes, both in animals and plants. In our human body, nitrogen is the building block of DNA, protein and each amino acid, nucleotide.

In plants, nitrogen is an indispensable component to make chlorophyll, the compound that is helping them photosynthesize, take in CO ₂ , sequester carbon and release oxygen. Lack of nitrogen or lack of nitrogen, plants will become stunted, unable to produce leaves. Lack of chlorophyll causes leaves to turn yellow and photosynthesis will be affected.

This should have happened to seagrasses as they made their way from the ground to the ocean floor. That's because unlike algae that can take nitrogen from water and convert nitrogen into ammonia or nitrate for use on their own, seagrasses are descendants of plants, so they are required to take nitrogen from the soil, through the process of fixation. proteins made by bacteria .

In plants, nitrogen is an indispensable component to make chlorophyll.

Even the atmosphere is filled with nitrogen, but plants can't take it up to live. They need bacteria to convert nitrogen into forms of compounds that the roots take up, such as ammonia or nitrate, for the plants to use. This conversion process is called nitrogen fixation . But the sad news is that the bottom of the sea doesn't contain as many nitrogen-fixing bacteria as efficiently as on land.

This suggests that something else must have converted and provided nitrogen for the seagrass to grow. Wiebke Mohr, an ocean biologist from the Max Planck Institute in Bremen, Germany was curious about this question.

In one of his studies, he and his colleagues collected Neptune seagrass (Posidonia oceanica) in the Mediterranean and the sediments around it. After bringing them back to the lab, they'll stain the specimens with different dyes, highlighting each species of bacteria present.

The results revealed the presence of a completely new strain of bacteria in the roots of the seagrass. Mohr and his colleagues named the bacterium Celerinatantimonas neptuna, and they noticed that C. neptuna is often abundant in seagrass roots during the summer, when nitrogen is most scarce. It seems that these are the bacteria that help seagrass fix nitrogen.

The bacterium Celerinatantimonas neptuna seems to help seagrass fix nitrogen.

"Previously other scientists thought that the so-called fixed nitrogen that seagrasses use came from bacteria that live around their roots on the seafloor. But now, we have shown that this is a much closer relationship: 

Nitrogen-fixing bacteria live just inside the roots of seagrasses, not outside and in the soil. This is the first time that such an intimate symbiosis has been demonstrated in seagrasses," said Mohr.

Two companions

On land, we have legumes that also harbor nitrogen-fixing bacteria right inside their roots, where they form nodules. But this type of symbiotic relationship has never been observed in any marine plant species.

Now, Mohr and his colleagues have shown that Mediterranean seagrasses also carry a nitrogen-fixing bacterium, C. neptuna, in their roots. But because the bacterium's relatives are found in all parts of the world, Mohr thinks similar symbiotic relationships may also occur with other seagrass species, in other seas.

The bacterium C. neptuna greatly benefits from a symbiosis with seagrasses. They need energy to function, because converting nitrogen into ammonia or nitrite takes a lot of energy. The seagrass provided a home, and also the sugar molecules, to feed the bacteria.

In return, C. neptuna will fix nitrogen for them. After obtaining nitrogen from the roots, seagrasses will quickly bring this element up to feed their leaves and enhance photosynthesis. "This transfer is very rapid, with about 20% of the new fixed nitrogen assimilated into the leaf biomass within 24 hours, " said Mohr and the new study authors.

Staining the specimens with different dyes, the scientists found bacteria that help seagrass fix nitrogen.

This symbiotic system has been running smoothly for hundreds of millions of years, and it is clear that C. neptuna plays a decisive role in the seagrass migration from the ground into the ocean. But where the bacteria came from is still unclear.

While Mohr found genetic evidence that the ancestors of C. neptuna were symbiotic with seaweed, a rootless species, he also found that the bacteria's closest living relatives were symbiotic. born with salty marsh grass.

Therefore, there are two theories, one is that C. neptuna abandoned seaweed to follow sea grass. Or this friendship was formed earlier, when the seagrasses were still in the mangrove swamps, they befriended C. neptuna and then carried their friend into the ocean.

Why do we need to protect this friendship and ecosystem?

Regardless of how and when seagrasses got C. neptuna's help, their combination today not only writes a success story for the friendship itself, but for a whole ecosystems in the ocean and on the land surface.

Seagrass beds are shelters and rich sources of food for many marine species. The foliage of seagrasses is a hiding place, incubation and habitat for small invertebrates such as shrimp, crabs, small fishes, juveniles and even larger fish.

Seagrass beds are shelters and rich sources of food for many marine species.

Seagrass is also the food of many marine species, including endangered species such as manatees, green turtles, and sea snakes. Every day, an adult manatee can consume about 28 to 40 kg of seagrass, an adult sea turtle consumes about 2 kg. If the seagrass disappears, these animals will have nothing to eat.

Not only having an important role for the ocean, seagrass is also a huge reservoir of CO2 for the atmosphere. Just like land plants, seagrasses absorb CO2 from the air and release oxygen during their life.

As the seagrass dies and decomposes on the seafloor, the previously absorbed CO2 is buried in the ocean's sediments. Currently, seagrass populations are helping us to store about 27.4 million tons of CO2 in about 600,000 square kilometers of the continental shelf.

It is a pity that we are destroying sea grasslands at an even faster rate than tropical rainforests. According to statistics, 18% of seagrass areas worldwide have disappeared in the past few decades alone. The number is equivalent to an area of ​​over 30,000 square kilometers.

WWF Seagrass Conservation Project: Sow 1 million seeds, plant 1 million hopes.

Every hour, the world will lose an area of ​​seagrass equivalent to 2 football fields. This happens mainly due to human activities that contaminate the seabed with solid waste, heavy metals, floating residues or oil spills.

In addition, fishing activities that use mines, chemicals, and bottom trawling can also destroy the seabed grass. Since seagrasses usually live in shallow water, reclamation activities, construction of structures such as roads, houses, harbors and even aquaculture will also affect the ecology of the seagrass fields outside. below.

Given the extent of this ecosystem's important contribution to the health of the planet, it's time to raise awareness among citizens, organizations and governments about them, seagrasses and micro-organisms. symbiotic bacteria in the roots.

And studies like that of Mohr and colleagues are helping to accelerate that process. The more we understand about seagrasses and the factors that help them thrive, the better we can take steps to preserve and restore this important ecosystem.