Seagrass excretes sugars to their rhizosphere making them the sweet spots in the sea [article]

Emilia Margaret Sogin, Dolma Michellod, Harald Gruber-Vodicka, Patric Bourceau, Benedikt Geier, Dimitri Meier, Michael Seidel, Philipp Hach, Gabriele Procaccini, Nicole Dubilier, Manuel Liebeke
2019 bioRxiv   pre-print
Seagrasses are one of the most efficient natural sinks of carbon dioxide on Earth. Despite covering less than 0.1 % of coastal regions, they have the capacity to bury up to 10 % of marine organic matter and can bury the same amount of carbon 35 times faster than tropical rainforests. On land, the soils ability to sequestrate carbon is intimately linked to microbial metabolism. Despite the growing attention to the link between plant production, microbial communities, and the carbon cycle in
more » ... strial ecosystems, these processes remain enigmatic in the sea. Here, we show that seagrasses excrete organic sugars, namely in the form of sucrose, into their rhizospheres. Surprisingly, the microbial communities living underneath meadows do not fully use this sugar stock in their metabolism. Instead, sucrose piles up in the sediments to mM concentrations underneath multiple types of seagrass meadows. Sediment incubation experiments show that microbial communities living underneath a meadow use sucrose at low metabolic rates. Our metagenomic analyses revealed that the distinct community of microorganisms occurring underneath meadows is limited in their ability to degrade simple sugars, which allows these compounds to persist in the environment over relatively long periods of time. Our findings reveal how seagrasses form blue carbon stocks despite the relatively small area they occupy. Unfortunately, anthropogenic disturbances are threatening the long-term persistence of seagrass meadows. Given that these sediments contain a large stock of sugars that heterotopic bacteria can degrade, it is even more important to protect these ecosystems from degradation.
doi:10.1101/797522 fatcat:loeil25ambevjl4wzlvm7inw3y