From Science Matters

By Ron Clutz

From the Advanced Science Research Center, GC/CUNY Earth Has Too Much Nitrogen – and Too Little Nitrogen – at the Same Time.  Excerpts in italics with my bolds

Multi-institutional research team finds declining
nitrogen availability in a nitrogen-rich world.

Since the mid-20th century, research and discussion have focused on the negative effects of excess nitrogen on terrestrial and aquatic ecosystems. However, new evidence indicates that the world is now experiencing a dual trajectory in nitrogen availability. Following years of attention to surplus nitrogen in the environment, our evolving understanding has led to new concerns about nitrogen insufficiency in areas of the world that do not receive significant inputs of nitrogen from human activities. In a new review paper, “Evidence, Causes, and Consequences of Declining Nitrogen Availability in Terrestrial Ecosystems,” in the journal Science, a multi-institutional team of researchers describes the causes of declining nitrogen availability and how it affects ecosystem function.

Over the last century, humans have more than doubled the global supply of reactive nitrogen through industrial and agricultural activities. This nitrogen becomes concentrated in streams, inland lakes, and coastal bodies of water, sometimes resulting in eutrophication, low-oxygen dead zones, and harmful algal blooms. These negative impacts of excess nitrogen have led scientists to study nitrogen as a pollutant. However, rising carbon dioxide and other global changes have increased demand for nitrogen by plants and microbes, and the research team’s newly published paper demonstrates that nitrogen availability is declining in many regions of the world, with important consequences for plant growth.

[Note the Nitrogen Deposition graph in the top diagram. It peaked in the 1980s, yet in 2023 it is being used to force farmers off their land in the Netherlands,Canada, Ireland and other nations to come]

Nitrogen is an essential element for plants and the animals that eat them. Gardens, forests, and fisheries are all more productive when they are fertilized with nitrogen. If plant nitrogen becomes less available, trees grow more slowly and their leaves are less nutritious to insects, potentially reducing growth and reproduction, not only of insects, but also the birds and bats that feed on them.

“When nitrogen is less available, every living thing holds on to the element for longer, slowing the flow of nitrogen from one organism to another through the food chain. This is why we can say that the nitrogen cycle is seizing up,” said Andrew Elmore, senior author on the paper, and a professor of landscape ecology at the University of Maryland Center for Environmental Science and at the National Socio-Environmental Synthesis Center.

On top of increasing atmospheric carbon dioxide, rising global temperatures also affect plant and microbial processes associated with nitrogen supply and demand. Warming often improves conditions for growth, which can result in longer growing seasons, leading plant nitrogen demand to exceed the supply available in soils. Disturbances, including wildfires, can also remove nitrogen from systems and reduce availability over time.

Our evolving understanding of the Earth system has led to new concerns about N insufficiency after years of attention to surplus N in the environment. An integrated suite of responses will be needed to simultaneously manage both of these problems. Given the potential implications of declining N availability for food webs, carbon sequestration, and other ecosystem functions and services, it is important that research, management, and policy actions be taken before the consequences of declining N availability become more severe. It can be difficult to create a shared understanding of the N cycle and the many effects of N on ecosystem health and human well-being. The combination of excess N and declining N availability, in which outcomes vary widely across landscapes, adds to this challenge. Developing dialogues among diverse stakeholders—scientists, ecosystem managers, and others—will be necessary for alleviating and adapting to declining N availability in an N-rich world.