Since the beginning of the twentieth century, terrestrial ecosystems have experienced an accelerated decline in nitrogen availability. In a new study, a group of researchers has demonstrated the existence of this evolution while detailing its causes and consequences. The results were published in the journal Science on April 15.
A large body of study has focused on the ins and outs of excess nitrogen in terrestrial and aquatic ecosystems. We find, for example, this scenario around agricultural areas with crops enriched with reactive nitrogen. When these inputs escape to lakes, rivers or coasts, they can induce eutrophication of the environment, the proliferation of algae and the development of dead zones.
However, a group of researchers recently discovered that the planetary environment is also under stress from a nitrogen deficit. Indeed, for many non-agricultural terrestrial ecosystems, observations echo a rapid drop in nitrogen availability since the beginning of the twentieth century. As the curve below shows, the downtrend is clearly unfolding at an increasingly rapid pace.
Decline in nitrogen availability: what causes and what consequences?
Since nitrogen is a building block of plant proteins, any decrease in its availability in the environment will affect the growth of insects and mammals that feed on it. The impact is in fact the opposite of that of fertilization. Plants are less nutritious, insects and animals grow and reproduce less quickly and eventually, all or part of the ecosystem tends to operate in slow motion.
At the origin of this nutritional decline, the researchers place the increase in the quantity of carbon dioxide (CO2) in the air and the general rise in temperatures. As air richer in CO2 tends to favor plant growth, the demand for nitrogen is higher than what the environment is able to offer, causing a drop in its concentration in plants and soils. The same goes for a warmer and more humid environment.
“Strong evidence of declining nitrogen availability in many places and settings is another important reason to rapidly reduce our reliance on fossil fuels,” said Andrew Elmore, one of the study’s co-authors. “Management responses that could increase nitrogen availability over large areas are likely to be controversial, but are clearly an important area for study.”