What does drought have to do with sequestering CO2 in the soil?
Drought also impacts the CO2 cycle in forest ecosystems
(Sustainabilityenvironment.com) – Drought decreases the ability of soils to seize CO2. How? Slowing down the activity of earthworms, a hidden but fundamental element to transform organic matter into nutrients and, in the process, to fix CO2 in the soil. This was established by a long-term study conducted by the Swiss Federal Institute for Forest, Snow and Landscape Research in the canton of Valais.
For 19 years, researchers at the Swiss Institute have been working on a number of pine wood particles that are particularly exposed to water shortages. While part of the soil is regularly irrigated, the remaining portion is left in natural conditions without any intervention. In this way, the study investigates the effects on the carbon cycle, the rate of decomposition of forest litter, and also manages to clarify the role of the organisms that mediate it – such as earthworms.
Result? Many more earthworms were found in irrigated plots than in non-irrigated ones. But not only them. The same result applies to smaller organisms, such as Collembolas and cochineals, all of which are fundamental for the decomposition of the layer of organic materials deposited on the soil surface. “If forest soils become too dry, this inhibits activity and the amount of organisms in the soil and forests can absorb less carbon in the long term,” explains study director Frank Hagedorn.
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What happens to earthworms and other litter organisms? The drought causes them to hide deeper, to chase the moisture of the soil, but in doing so they no longer work at the decomposition of the litter. Or the lack of water triggers their quenching, a process of self-defense with which these organisms protect themselves from excessive heat and unfavorable conditions by limiting their activity.
One process, that of the impoverishment of the soils because of the scarcity of water, that happens in extremely fast times. “Soil humus forms over hundreds or thousands of years. We didn’t expect to see differences in the levels of carbon stored after only ten years,” the scientist concludes.