Conservation

Rare and native plant species are more likely than abundant or invasive species to be lost from an ecosystem when nitrogen is made more available. Nitrogen increases plant growth, but appears to give a competitive edge to some plants, and a disadvantage to plants that are not adapted to take advantage of more nutrition. This is the conclusion of a wide-ranging nitrogen fertilization experiment by Katherine Suding and her colleagues at UC Irvine. The study was published in PNAS.

Nitrogen in soil comes from nitrogen fixation by certain plants and microorganisms, by lightning-fixation in rainfall, and from manmade sources. The most important manmade sources include fertilizer and acid rain. While fertilizer is not applied intentionally to natural ecosystems, it can arrive in the wind from agricultural sources. Acid rain contains sulfuric and nitric acids from industrial pollution, and is adding considerable amounts of nitrogen to natural ecosystems.

The ecological consequences of nitrogen addition are made clear by this study. Increased nitrogen from anthropogenic sources will reduce biodiversity, eliminate rare species and favor aggressive, fast-growing species including invasives.

As landscaping in urban areas moves toward native plants, it is important to recognize that excess nitrogen fertilization will promote the growth of weeds and non-natives, which have been selected to do well in high-nitrogen environments.