Iceland, a window into the future of Arctic soil in an increasingly warm world

The Icelandic town of Hveragerði has around 3,000 inhabitants and is surrounded by a landscape dotted with fumaroles of smoke and steam emanating from the earth. One of the things that makes this region special is that an earthquake in 2008 caused the appearance of natural geothermal gradients . These gradients heat the soil at different intensities – between 0.5°C and 40°C above ambient temperature – and turn it into a real laboratory to study live how soil warming will affect the planet's cold ecosystems. It is in this unique environment where, since 2015, CREAF researcher and professor at the Autonomous University of Barcelona, Sara Marañón, has been leading the SOCRATES project . The research results are not limited to Iceland, but are a window into the future of what can happen on a global level if we continue to 'add degrees'.

"One of our challenges is to understand what exactly happens in these first years of warming on land, what we know as the 'destabilization cascade': a 'domino effect' that affects microorganisms, roots and vegetation before the ecosystem manages to stabilize again," explains Marañón.

In this sense, one of the findings of the project reveals that in the first years of soil warming the ecosystem undergoes a super-reaction : the metabolism of microorganisms accelerates, carbon is released into the atmosphere and the composition of the soil changes. However, in the long term, it reaches a new equilibrium in which abrupt changes are no longer observed: the species of living beings are different or have adapted and, although there is a lower concentration of carbon, nitrogen and organic matter in the soil, the ecosystem has reached a new steady state. "The problem is that, even if it stabilizes, in the process, old atmospheric carbon that had been stored for centuries is irreversibly released, among other consequences," warns Marañón.

Another result that the team recently published is that 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 global balance of greenhouse gases to increase in an irreversible and unexpected way.

Among the reasons, they point out that the natural nitrogen cycle is out of balance: due to the heat, microorganisms are activated in winter, when plants do not yet need it, and the nutrient is lost. Another reason is that heat “thins” microbial biomass and, therefore, they are able to retain less nitrogen. As a result, some of this nitrogen can leak into groundwater in the form of nitrates and can contaminate aquatic systems. Another part can be released as nitrous oxide, a greenhouse gas almost 300 times more potent than CO₂ .

Every summer, a multidisciplinary and international team travels to Iceland to collect samples and conduct live experiments. At this time, you can see the team transplanting soil cylinders to warmer areas and extracting those they placed in previous years. When the cylinders are extracted, the procedure is exhaustive: the University of Iceland separates the samples into fractions – green vegetation, dry vegetation, roots and soil – and, from Reykjavik, the samples travel to Barcelona, where Sara Marañón coordinates several experiments in the laboratory. For example, measuring soil respiration and CO₂ emissions ; the size of microbial biomass and the respiration of microorganisms; also the nitrogen transformations - processes such as ammonification and nitrification - that mark soil fertility, among other things. "These tests seek to test one of the central hypotheses of the project: that with warming, the demand for carbon by microorganisms increases, while the capacity to retain nitrogen decreases," says the researcher.

But that's not all, other partners are adding more pieces to the puzzle. For example, a team from the University of Antwerp (Belgium) is focusing on changes in the composition of microbial communities in soils subjected to high temperatures. Their task is particularly delicate: in order not to lose information, the samples must be frozen immediately in the field. To do this, they use special backpacks with liquid nitrogen , where the samples are stored in small tubes that remain intact until their analysis in the laboratory. Another team from the University of Tartu (Estonia) is focusing on studying roots . To do this, they use an ingenious method: they install vertical meshes, similar to mosquito netting, which allow them to follow the growth of the roots as they pass through the fabric. This system offers a precise view of how plants respond to temperature changes in the subsoil.

“These results help us predict what may happen in Arctic ecosystems if temperatures continue to rise and detect the first signs of destabilization,” concludes Marañón.

The SOCRATES project is led by CREAF and also involves the University of Barcelona, the University of Vienna in Austria and the Agricultural University of Iceland. In addition, the project operates in collaboration with the ForHot Consortium, which was initiated by a group of scientists from various international entities, convinced that Iceland is the best European laboratory for studying global warming on land.