Arctic soil is running out of nitrogen due to warming, its emissions are skyrocketing

Rising temperatures due to global warming are causing Arctic soil to lose nitrogen, an essential nutrient for plants. Lacking this food, they grow less and therefore have less capacity to absorb and retain CO2, according to a study led by the Center for Ecological Research and Forestry Applications (CREAF) and the Autonomous University of Barcelona.

The opposite of what was thought

Half of the planet's carbon remains stored in the frozen soils of the Arctic and Subarctic, which cover regions such as Greenland, Canada, Alaska, Scandinavia, and Iceland. Until now, what was known was that with warmer temperatures, the microorganisms living in this ecosystem are more active, consume more carbon, and emit it in the form of CO2 into the atmosphere.

However, the new study, published in Global Change Biology, reveals previously unforeseen consequences: heat also causes soils to become depleted of nitrogen, an essential nutrient for plants.

Without enough nitrogen, vegetation grows less than expected and is unable to absorb as much CO2 or offset emissions generated from the soil, causing the overall balance to increase irreversibly and unexpectedly .

Specifically, for every additional degree of temperature, between 1.7% and 2.6% of nitrogen is lost from the soil, which leads to a proportional loss of carbon in the form of CO2 to the atmosphere.

Ten years of experimentation in Iceland

The discovery was made thanks to a ten-year experiment in Iceland, a "natural laboratory" where, thanks to geothermal activity, ground temperature increases of between 0.5 and 40°C above ambient are achieved, and where it is possible to observe live what happens when the ground at high latitudes warms.

"We already knew that climate change is releasing more CO2 from Arctic soils, but we believed that some of these emissions were offset by plant growth, which increases slightly with warming.

However, the study shows the opposite: nitrogen is lost, soil fertility decreases, and as a result, Arctic ecosystems cannot offset these microbial CO2 emissions,” according to the researcher who led the study, Sara Marañón.

Decoupling between supply and demand

Under normal conditions, microorganisms are most active in spring and summer, consuming nitrogen and transforming it into ammonium and nitrates, compounds that plants use for food.

However, with rising temperatures, this process is becoming desynchronized: microorganisms are already "wide awake" in winter, when plants are still dormant due to lack of light and do not need this nutrient input, which causes "a decoupling between supply and demand."

The result: the transformed nitrogen is unused and lost. Some can seep into groundwater in the form of nitrates and contaminate aquatic systems, while another portion can be released as nitrous oxide, a greenhouse gas nearly 300 times more potent than CO2.

Furthermore, the soil's capacity to store nitrogen decreases at higher temperatures, due, among other reasons, to the fact that heat reduces the number and size of microorganisms, as well as the number of fine roots, natural stores of nitrogen, which means that fewer and fewer reserves are available.

According to the same source, the greatest nitrogen leaks occur during the thaw, because this is the period when this "natural store" of nitrogen is most abundant and plants have not yet grown to absorb it. EFEverde