Important weapon in the fight against climate change also appears to produce enormous amounts of sugar

Worldwide, there is a million tons of sucrose hidden under sea grasses – enough for 32 billion cans of Coke!

Seagrasses form lush green pastures in many coastal areas around the world. And they are also vital. For example, these grasses not only provide good water quality and shelter a number of animals, they also store a lot of carbon, making them an important weapon in the fight against climate change. However, a new study proves that we didn’t know everything about these essential plants yet. Because scientists have now discovered that seagrasses produce enormous amounts of sugar.

Researchers have stumbled upon sweet spots in the sea. Because in the new study, they found that seagrasses contain enormous amounts of sugar, largely in the form of sucrose.

Coke

The sugar concentrations in the soil enclosing the roots of seagrass — known as the rhizosphere — are at least 80 times higher than in other marine environments, the team reveals. “To put this in perspective, we estimate that there are between 0.6 and 1.3 million tons of sugar, mainly in the form of sucrose, in the seagrass rhizosphere worldwide,” explains researcher Manuel Liebeke. “That’s roughly equivalent to the amount of sugar in 32 billion cans of Coke!”

Photosynthesis

Why do seagrasses dump so much sugar? “Seagrasses produce sugar during photosynthesis,” explains researcher Nicole Dubilier. “Under average light conditions, these plants use most of the sugars they produce for their own metabolism and growth. But under high light conditions, for example in the afternoon or in summer, the plants produce more sugar than they use or store. Then they release the excess sucrose into their rhizosphere.”

Micro organisms

It is surprising that this mountain of sugar then remains. Normally, micro-organisms quickly consume any free sugars in their environment. Microbes love sugar: it is easy to digest and it is packed with energy. So the question is, why isn’t all the sucrose hiding under lush seagrasses consumed by the large community of microorganisms that reside in the rhizosphere?

phenols

“It took us a long time to answer that question,” said researcher Maggie Sogin. “What we eventually realized is that seagrass – like many other plants – secrete and release phenolic compounds into their sediments.” Phenols may sound familiar to you. For example, red wine, coffee and fruit are full of phenols and many people also take them as dietary supplements. What is less well known is that phenols are antimicrobials and inhibit the metabolism of most microorganisms. “In our experiments, we isolated phenols from seagrass and added them to the microorganisms in the rhizosphere of seagrass,” explains Sogin. “And indeed: much less sucrose was consumed compared to when phenols were not present.”

carbon dioxide

It’s a good thing that these microbes leave the sugar for what it is. “Our calculations show that if the sucrose found were broken down by microbes, this would release at least 1.54 million tons of carbon dioxide into the atmosphere worldwide,” says Manuel Liebeke. “That’s roughly equivalent to the amount of carbon dioxide that 330,000 cars emit in a year.”

Heavy weather

Despite the important role seagrasses play in our fight against climate change, these plants are in dire straits. For example, seagrass beds are even among the most threatened habitats on earth. Seagrasses are declining at an alarming rate in all oceans; annual losses are estimated at seven percent in some places, comparable to the loss of coral reefs and tropical rainforests. A third of all the seagrass on Earth may have already been lost.

According to the researchers, we should do more to save these vital plants and secure the future of seagrass. “Our study highlights the importance of preserving these carbon sinks,” concludes Sogin.