Scientists dis­covered vast amounts of sug­ar un­der­neath seagrass mead­ows

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Seagrasses- marine plants- are one of the most ef­fi­cient global sinks of car­bon di­ox­ide on Earth. They stores al­most twice as much car­bon as forests on land and 35 times as fast.

Recently, scientists from the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy in Bre­men, Ger­many, found that seagrasses re­lease massive amounts of sugar into their soils, called rhizo­sphere. They release more than 1 million tons of sucrose- at least 80 times higher than pre­vi­ously meas­ured in mar­ine en­vir­on­ments.

Study authors noted, “Such high concentrations of sugar are surprising.”

Manuel Liebeke, head of the Re­search Group Meta­bolic In­ter­ac­tions at the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy said, “To put this into per­spect­ive: We es­tim­ate that world­wide there are between 0.6 and 1.3 mil­lion tons of sugar, mainly in the form of sucrose, in the seagrass rhizo­sphere. That is roughly com­par­able to the amount of sugar in 32 bil­lion cans of coke!”

Nicole Du­bilier, Dir­ector at the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy ex­plains, “Seagrasses pro­duce sugar dur­ing pho­to­syn­thesis. Un­der av­er­age light con­di­tions, these plants use most of the sug­ars they pro­duce for their meta­bol­ism and growth. But un­der high light con­di­tions, for ex­ample at mid­day or dur­ing the sum­mer, the plants pro­duce more sugar than they can use or store. Then they re­lease the ex­cess sucrose into their rhizo­sphere. Think of it as an over­flow valve.”

Microbes are sugar lovers: they consume any free sugars in their environment. But, they do not consume sucrose. Why?

To figure this out, scientists conducted experiments in which they added hen­olics isol­ated from seagrass to the mi­croor­gan­isms in the seagrass rhizo­sphere. In­deed, much less sucrose was con­sumed com­pared to when no phen­olics were present.

First, au­thor Mag­gie So­gin, who led the re­search off the Italian is­land of Elba and at the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy said, “What we real­ized is that seagrass, like many other plants, re­lease phen­olic com­pounds to their sed­i­ments. Red wine, cof­fee, and fruits are full of phen­olics, and many people take them as health sup­ple­ments. What is less well known is that phen­olics are an­ti­mi­cro­bi­als and in­hibit the meta­bol­ism of most mi­croor­gan­isms.”

Surprisingly, despite the difficult conditions, a small group of mi­cro­bial spe­cial­ists can thrive on sucrose. So­gin spec­u­lates that these sucrose spe­cial­ists can not only digest sucrose and degrade phenolics but also provide benefits to the seagrass by producing nu­tri­ents it requires to develop, such as nitrogen.

Sogin said, “Such be­ne­fi­cial re­la­tion­ships between plants and rhizo­sphere mi­croor­gan­isms are well known in land plants, but we are only just be­gin­ning to un­der­stand the in­tim­ate and in­tric­ate in­ter­ac­tions of seagrasses with mi­croor­gan­isms in the mar­ine rhizo­sphere.”

Liebeke said, “Look­ing at how much blue car­bon – that is car­bon cap­tured by the world’s ocean and coastal eco­sys­tems – is lost when seagrass com­munit­ies are decim­ated, our re­search clearly shows: It is not only the seagrass it­self but also the large amounts of sucrose un­der­neath live seagrasses that would res­ult in a loss of stored car­bon. Our cal­cu­la­tions show that if the sucrose in the seagrass rhizo­sphere was de­graded by mi­crobes, at least 1,54 mil­lion tons of car­bon di­ox­ide would be re­leased into the at­mo­sphere world­wide.”

So­gin said“That’s roughly equi­val­ent to the amount of car­bon di­ox­ide emit­ted by 330,000 cars in a year. Seagrasses are rap­idly de­clin­ing in all oceans, and an­nual losses are es­tim­ated to be as high as 7% at some sites,­ com­par­able to the loss of coral reefs and trop­ical rain­forests. Up to a third of the world’s seagrass might have been lost. We do not know as much about seagrass as we do about land-based hab­it­ats. Our study con­trib­utes to our un­der­stand­ing of one of the most crit­ical coastal hab­it­ats on our planet and high­lights how im­port­ant it is to pre­serve these blue car­bon eco­sys­tems.”

Journal Reference:

  1. E. Mag­gie So­gin, Dolma Michel­lod, Har­ald Gruber-Vodicka et al. Sug­ars dom­in­ate the seagrass rhizo­sphere. Nature Eco­logy & Evol­u­tion (2022). DOI: 10.1038/s41559-022-01740-z

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