Nitrogen’s Mixed Blessing: A Tale of Two Prairies

Anthropogenic tinkering has flooded global ecosystems with reactive nitrogen, effectively turning the planet into an unintended fertilisation experiment. A recent five-year study in the US Central Plains has illuminated precisely how this chemical windfall affects grasslands, revealing a stark divide dictated by local climate.

Researchers applied varying levels of nitrogen to two distinct environments: the parched semi-arid shortgrass steppe and the moister mesic tallgrass prairie. The results offer a fascinating paradox. In the thirsty shortgrass steppe, the extra nitrogen failed to boost overall productivity; the plants simply lack the water to capitalise on the nutrient buffet. However, the community composition shifted significantly once nitrogen inputs hit a critical threshold of 5 g m-2.

Conversely, the verdant tallgrass prairie behaved like a glutton. Productivity surged at the same 5 g m-2 threshold before plateauing, yet the actual lineup of plant species remained largely unchanged. While both ecosystems suffered a drop in species richness—a worrying trend for biodiversity—the study underscores a vital nuance: an ecosystem’s growth and its botanical makeup can respond to pollution in entirely separate ways. It appears that while nitrogen pulls the strings, water sets the stage.