Scientists Found a Nitrogen-Fixing Seagrass

By Brian Owens.

The meadows of luscious green seagrass that dot coastal regions around the world are gaining recognition as important marine habitats and carbon sinks, but there is still a lot we don’t know about how these marine plants live. For example, scientists have assumed that seagrasses, like many other marine plants, take up important nutrients like nitrogen directly from the surrounding seawater and sediment. But a new study shows that seagrasses actually use a technique to acquire nitrogen that is prevalent among beans, peas, and other legumes on land, but is exceedingly rare in the ocean: they have a symbiotic relationship with nitrogen-fixing bacteria.

In the Mediterranean Sea, Neptune seagrass grows in vast meadows. Yet nutrients, says Wiebke Mohr, a marine microbiologist at the Max Planck Institute for Marine Microbiology in Bremen, Germany, are virtually absent in the water. “We knew it must have a different source of nutrients,” she says.

Mohr and her colleagues knew that nitrogen-fixing bacteria—bacteria that convert nitrogen gas into ammonia, a form of the element that plants can use—would be involved in some way, either living on the surface of the plants’ roots or in the surrounding sediment.