Phys.org October 17, 2022
Diazotrophs are widespread microorganisms that alleviate nitrogen limitation in 60% of our oceans, thereby regulating marine productivity. Yet, the group-specific contribution of diazotrophs to organic matter export has not been quantified. An international team of researchers (France, Israel, Spain) examined the fate of five groups of globally distributed diazotrophs by using an original combination of mesopelagic particle sampling devices across the subtropical South Pacific Ocean. They demonstrated that cyanobacterial and non-cyanobacterial diazotrophs are exported down to 1000 m depth. Phycoerythrin-containing UCYN-B and UCYN-C-like cells were recurrently found embedded in large organic aggregates or organized into clusters of tens to hundreds of cells linked by an extracellular matrix, presumably facilitating their export. They show that, when diazotrophs are found in the euphotic zone, they are also systematically present in mesopelagic waters, suggesting their transport to the deep ocean. They concluded that diazotrophs are a significant part of the carbon sequestered in the deep ocean and, therefore, they need to be accounted in regional and global estimates of export…read more. Open Access TECHNICAL ARTICLEÂ
Quantification of diazotrophs in sediment traps. Credit: The ISME Journal (2022)Â