Pollution

Nitrogen levels on a decline in ‘nitrogen-rich world’, plants and animals may face consequences: Study

Tropical and boreal forests may be particularly vulnerable

 
By Rohini Krishnamurthy
Published: Monday 18 April 2022

An imbalance in nitrogen availability has been reported across the globe, with some places having an excess and others a shortage of the element, according to a new report. 

This has been hurting aquatic and terrestrial life that feed on it and after several years, the new analysis published in Science has quantified the problem. 

“There is both too much nitrogen and too little nitrogen on Earth at the same time,” Rachel Mason, lead author of the paper and a former postdoctoral scholar at the National Socio-environmental Synthesis Center, said.

Without nitrogen, an essential nutrient, plants grow slowly and produce smaller flowers and fruits. Their leaves turn yellowish and are less nutritious to insects, birds and animals.

The issue of declining nitrogen availability is not new. “It has been on the scientific radar for a long time,” Mason told Down To Earth. 

However, the evidence was scattered across scientific communities, she added. So, a team of researchers from multiple institutions pieced the evidence together to get a complete picture. They also looked at questions such as the reasons causing the decline and the consequences.

Nitrogen availability has been shrinking in grasslands in central North America for a hundred years, the review noted. Cattle grazing these areas have had less protein in their diets over time, it added.

Many forests in North America and Europe have also suffered from nutritional declines for several decades or longer due to the same reason, the researchers said in the study.

Tropical and boreal forests may be particularly vulnerable, Mason added.

Plants grow quickly when exposed to high carbon dioxide (CO2) concentrations. Thus, their demand for nitrogen also goes up, the experts wrote in the review.

High CO2 levels dilute plant nitrogen, triggering a cascade of effects that lower the availability of nitrogen. Other factors contributing to nitrogen decline include warming and disturbances, including wildfire, they said.

Declining nitrogen availability can be linked to insect apocalypse, Mason said. Plants with low nitrogen levels can encourage swarming in some species of locusts, she added.

Further, low nitrogen availability could limit plants’ ability to capture CO2 from the atmosphere, the review warned. 

“The strong indications of declining nitrogen availability in many places and contexts are another important reason to rapidly reduce our reliance on fossil fuels,” Andrew Elmore, professor of landscape ecology at the University of Maryland Center for Environmental Science and the National Socio-environmental Synthesis Center, said.

Sprinkling nitrogen fertilisers in regions facing a shortage of nitrogen supply may not be the answer. “We don't have a good track record of adding nitrogen in the right place, at the right time, in the right amount,” Mason said.

Human production of nitrogen is now five times higher than it was 60 years, according to a 2017 study.

When excessive nitrogen accumulates in the streams, inland lakes and coastal bodies of water, it could sometimes result in eutrophication, leading to harmful algal blooms, dead zones and fish kills, according to the National Oceanic and Atmospheric Administration. 

In humans, high levels of nitrogen in the groundwater are linked to intestinal cancers and miscarriages and can be fatal for infants, researchers cautioned.

The experts called for more support for research in the area as they have yet to completely understand it. “It's a difficult philosophical as well as a scientific and policy problem,” Mason said.

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