(ORDO NEWS) — Unlike algae, sea grasses are flowering plants that have mastered the seas relatively recently. Now their communities are stretched along the coasts, have a great influence on the climate and, as it turned out, also release enormous amounts of sucrose into the sea soil.
The flora of the seas is represented not only by ancient and primitive algae, but also by the so-called sea grasses.
These are flowering plants that have recently – by evolutionary standards – mastered the aquatic environment, namely the coastal strip of the seas, where they form dense thickets – sea meadows.
Seagrasses belong to four families: Posidoniaceae ( Posidoniaceae ), Eelgrasses ( Zosteraceae ), Waterflowers ( Hydrocharitaceae ), and Cymodoceaceae ( Cymodoceaceae ).
The ecosystems formed by these plants mean a lot for the climate, as they store carbon very efficiently. One square kilometer of sea grasslands holds twice as much carbon as the same area on land covered by forests. In addition, seagrass stockpiles this key element 35 times faster.
It was the sea meadows that attracted the attention of researchers from the Max Planck Institute for Marine Microbiology (Germany), who devoted a new article to them in Nature Ecology & Evolution.
Scientists have found that seagrass thickets release a lot of sugars, mainly sucrose, the same one that we add to coffee.
Recall that sugars are one of the classes of organic (containing carbon chains) substances that living organisms actively use, including for energy storage.
It accumulates in the so-called seagrass rhizosphere – in fact, in the soil surrounding the roots of plants. There, the concentration of sucrose is 80 times higher than the maximum previously described in marine ecosystems.
“Let’s look at the prospects: according to our data, the seagrass rhizosphere contains from 0.6 to 1.3 million tons of sugars, mainly sucrose,” said Manuel Liebeke of the Max Planck Institute for Marine Microbiology. “That’s about the same amount of sugar as 32 billion cans of cola.”
Actually, it’s rather strange. As a rule, organic substances are immediately used by bacteria and other microorganisms. Just like humans, microbes love sugar and consume it as soon as possible. What stops them in this case?
“We had to spend a lot of time on this issue,” said Maggie Sogin, who led this writing team . “We realized that sea grasses, like many other plants, release phenolic compounds into the soil.
In experiments, we added phenols isolated from sea grasses to microorganisms living in their rhizosphere, and made sure that the rate of consumption of sucrose in this case is much less than in a medium without phenols.
As a result, the sugar that no one got is buried under sea meadows, and the carbon contained in it is excluded from the global circulation of this element.
The question arises: why do underwater plants produce sugar in such huge quantities, and then still release it outside? The fact is that if sea meadows are under very intense lighting and photosynthesis in them is too active, then plants synthesize more sugar than they can use. They get rid of the excess by simply throwing it into the environment.
At the same time, some specialized microorganisms have learned to grow in the rhizosphere of marine meadows, despite phenolic compounds. Such microbes are able to destroy both sugars and phenols, and at the same time release substances valuable for plants, including nitrogen.
Such mutually beneficial relationships between plants and microorganisms in their rhizosphere have been studied in detail on land, but studies of such a symbiosis in sea grasses are just beginning.
The unexpected new result underscores the importance of marine grasslands for climate stability and the global carbon cycle.
Now the area of thickets of sea grasses is sharply reduced – in some places up to 7% per year. The authors’ predictions are alarming: according to their estimates, the complete loss of sea grasslands would lead to the release of 1.54 million tons of carbon dioxide into the atmosphere – the same amount emitted by 330,000 cars a year.
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