Drought, invertebrates, and carbon: the vicious cycle affecting soil and climate

Drought limits the action of invertebrates and their ability to store organic carbon in soil, according to research from Switzerland. A finding with obvious implications for climate change

by Matteo Cavallito

 

Drought limits the action of invertebrates with negative consequences for soil balance according to a recent research by the Swiss Federal Institute for Forest, Snow and Landscape Research. The study, published in the journal Global Change Biology, focuses in particular on the actions of earthworms, which, in excessively dry soils, act like other species sharing the ecosystem and use to go deeper searching for a more favorable environment.

In doing so, the specimens deprive the topmost layer of their notoriously precious services, which include decomposing dead leaves, releasing nutrients and capturing carbon. These actions contribute to maintaining soil fertility and countering climate change.

Soil fauna is highly sensitive to drought.

Conducted in the Finges forest in the canton of Valais, the study involved 17 years of analysis and measurements. The researchers explored different areas of soil, noting, for example, that there were many more earthworms in the areas that had been watered the most than in the driest areas. This had also been confirmed for other smaller organisms such as springtails and woodlice. Two species that play a key role in the decomposition of foliar litter.

“Our study shows that soil fauna is highly sensitive to natural drought, which leads to a reduced carbon transfer from organic layers to the mineral soil,” says the research. “In the longer term, this potentially affects soil organic carbon storage and, therefore, soil fauna plays a key but so far largely overlooked role in shaping soil organic carbon responses to drought.”

An important discovery for climate

The finding highlights the role of species that populate soil and on the role they play in carbon management and fertility protection. Invertebrates, the authors note, would be more sensitive to the effects of drought than other relevant players such as fungi and microorganisms that contribute to soil balance.

The implications are obvious. Indeed, invertebrates are crucial players in the process that leads to the storage of carbon in humus. If the amount trapped in the soil is reduced, emissions increase, thus contributing to climate change. Which, again, makes droughts more frequent.

“Soil humus forms over hundreds to thousands of years,” said Frank Hagedorn, Head of Biogeochemistry at the Swiss Institute and lead author of the research. “We didn’t expect to be able to see differences in the levels of carbon stored after just ten years.”

Europe experienced three “unprecedented” summer drought waves

During the 21st century, researchers recall, Europe experienced three “unprecedented” summer drought waves in 2003, 2015, and 2018. Extreme events that “severely affected the productivity and functioning of European forests and limited the metabolic activity of plants and soil biota.” A figure that is now back in the spotlight on Desertification and Drought Day celebrated by the UN on June 17.

The issue, after all, does not go unnoticed in the Continent where, according to the European Environment Agency, Portugal has suffered the greatest impact so far. Between 2000 and 2016, in fact, the country experienced a water deficit on 13.2 percent of its territory. Portugal is followed by Hungary (9 percent of the national soil) which has been affected by drought effects just like southern Balkans (Kosovo, Serbia and Albania), Iberian Peninsula (in the south) as well as parts of France and Germany. The consequences were most evident in terms of degradation of arable land and loss of pasture productivity.