Nitrogen is essential for plant growth—but too much of it can cause considerable damage. How forests regulate the nutrient depends not only on the trees, but also on the more inconspicuous plants in the lower layers—as a recent study by scientists at Friedrich Schiller University Jena shows. It shows that the plants in the herb and moss layer of a forest play a decisive role in how much nitrogen remains in the ecosystem and how much seeps into the lower layers of soil or water. The researchers report on their findings in the journal ?Plant and Soil?.

Moss as a particularly good filter

For their research, an interdisciplinary team from the University of Jena’s collaborative research centres ?AquaDiva? collected data for three different types of forest in the so-called Saale-Elster Sandstone Plate Observatory south of Jena. They installed sensors at 93 measuring points in beech, spruce and pine forests to record which and how many nutrients flow through the top soil layer over the course of a year. They discovered that where the vegetation on the ground is particularly dense, very little nitrogen was able to enter the soil.

Mosses in particular proved to be especially good filters that kept the nitrogen in the ecosystem and prevented it from seeping into the groundwater, for example. ?With our work, we have now been able to show that herbaceous plants and mosses in particular play a central role in the nutrient balance of the forest?, explains Till Deilmann from the University of Jena. ?They help to keep nitrogen in the system and are therefore involved in ensuring that soils are not burdened by excessive nitrogen input.?

The experts also investigated the role played by so-called functional traits of herbaceous plants—i.e. properties that indicate how they interact with their environment. They found, for example, that fast-growing plant species take up nitrogen more quickly, but also release it more quickly.

Look down more often