Seagrasses provide a vital habitat in shallow coastal seas. They also remove large amounts of CO2 from the atmosphere. Up to now, researchers have assumed that the plants take up nitrogen necessary for growth primarily from the seawater and sediment. However, in many regions where seagrasses thrive little nitrogen is available. Researchers of the Max Planck Institute for Marine Microbiology show that seagrass in the Mediterranean Sea lives in symbiosis with bacteria that reside in their roots and provide the much needed nitrogen. Such symbioses were previously only known from land plants.