Material cycles: There is a lack of nitrogen in nature
Analyzes of annual rings and leaves prove the lack of nitrogen in nature
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Fields are over-fertilized and contain large amounts of nitrogen. But the element is missing in nature, plants can no longer grow well. The high levels of carbon dioxide in the atmosphere seem to have something to do with it.
Snitrogen is essential to life, just like oxygen, water or carbon. Without nitrogen there would be no cells, no life. Because the element is essential for building proteins.
But this vital substance now seems to be becoming scarce in nature. American scientists warn that the content of usable nitrogen has been falling in many ecosystems for decades. There are now numerous observations that the decline in the nitrogen usable by microorganisms and plants is associated with the increased proportion of carbon dioxide (CO2) in the air.
An increase in temperature and changing rainy seasons could also play a role. The team around Andrew Elmore from National Socio-Environmental Synthesis Center in Annapolis (USA) has its overview study Published in the journal Science in 2022.
The researchers evaluated 100 scientific studies on various natural ecosystems. Whether the bound nitrogen was measured in the soil, in the water of streams and rivers or in parts of plants: a downward trend can be seen everywhere in these ecosystems.
When plants receive less nitrogen, they grow slower and the leaves are less nutritious. This leads to reduced growth in some insects and their predators and in some cases to fewer offspring. Plant nitrogen affects the entire food chain.
Nitrogen is also a key component of fertilizers. Therefore, in connection with intensive agriculture, there are also many areas with an oversupply of nitrogen compounds, which leads to algal blooms in water bodies and a decrease in dissolved oxygen in the water.
Connections are not fully understood
“There is too much nitrogen and too little nitrogen on Earth at the same time,” says Rachel Mason of the National Socio-Environmental Synthesis Center, lead author of the study. This is because the availability of nitrogen-containing compounds for plants and animals is very unequally distributed depending on the area.
The declining trend in available nitrogen in ecosystems began at different times, depending on the series of studies: when analyzing various so-called isotopes of chemical elements in annual rings, American researchers found the beginning of the trend around 1930. Measurements in lake sediments and leaf samples showed that the Nitrogen depletion started as early as the early 20th century.
The higher the carbon dioxide content in the atmosphere, the lower the nitrogen content in plants. This connection is shown by very different studies, even if the exact mechanism is not known. The increased carbon dioxide content in the air could lead to increased plant growth. One consequence of this could be an increased need for nitrogen, which is then lacking in natural cycles, the researchers write. However, there is still no comprehensive model for recognizing large-scale trends in the availability of nitrogen for plants and microorganisms.
The researchers complain that the connection between the carbon and nitrogen cycle is not shown by about half of the scientific models of the earth system. If it were taken into account, model calculations in terrestrial ecosystems showed a decline in carbon dioxide uptake capacity in the recent past.
Because protein uptake is associated with growth and reproduction in herbivores, declining nitrogen concentrations in leaves may contribute to a widespread decline in insect populations and adversely affect the growth of grazing livestock and wild herbivorous mammals, Elmore and colleagues write. They call for an annual report that provides scientists, environmental managers and policymakers with the state of the nitrogen cycle based on up-to-date measurements and analysis.
This article was first published in April 2022.
