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Spatial distribution of pores helps determine where carbon is stored in the soil

ScienceDaily
Spatial distribution of pores helps determine where carbon is stored in the soil

Date:
April 21, 2022
Source:
Helmholtz Centre for Environmental Research - UFZ
Summary:
Soils store more carbon than all the vegetation on the Earth's surface. However, there are still many unanswered questions about precisely which processes favor accumulation in the soil. Soil scientists have now developed a new method to show where and under what conditions carbon is stored f in the soil. It turns out, it is primarily the network of soil pores that controls the spatial distribution of carbon.
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Soils store more carbon than all the vegetation on the Earth's surface. However, there are still many unanswered questions about precisely which processes favour accumulation in the soil. Under the leadership of the Helmholtz Centre for Environmental Research (UFZ), a team of soil scientists have developed a new method to show where and under what conditions carbon is stored f in the soil. As they write in Nature Communications, it is primarily the network of soil pores that controls the spatial distribution of carbon.

In the public debate on climate protection, the importance of soil is often forgotten. However, soils store considerably more carbon globally than forests or the atmosphere. The long-term storage of carbon can be quite complex. On one hand, it depends on how much atmospheric carbon enters the soil through root growth, various mixing processes (e.g. soil cultivation or the activity of earthworms), and the seepage of dissolved organic compounds. On the other hand, it depends on whether the existing carbon in the soil can be stabilised or is decomposed by bacteria and fungi. Which process is more efficient -- storage or decomposition -- is determined primarily by the structure of the soil (e.g. the size of the network of pores that help transport air, water, and nutrients). "The carbon stored in plant residues and humus is not decomposed if bacteria or fungal hyphae are larger than the pores in the soil where it is stored," says Dr. Steffen Schlüter, UFZ soil physicist and lead author of the study. What's more: If the pores are permanently filled with water and thus without oxygen supply (e.g. in intact peat soils), bacteria find it more difficult to use the carbon. "One of the decisive factors for where carbon is stored in the soil is thus the spatial distribution of the pores," says Schlüter. It had previously not been possible to study the distribution pattern of the organic carbon within the millimetre and micrometre sized pores.

But the scientists at the UFZ have now managed to do this. With their new method, they can precisely localise the carbon in the soil. It is based on the staining of the organic compounds with osmium tetroxide, which sorbs onto the carbon-containing double bonds and is then visualised using X-ray computed tomography (CT). By scanning the soil sample before and after staining, the researchers can infer the distribution of the carbon from the differences in the images. Until now, this was possible only with the help of elaborate synchrotron CT methods. However, because there are only two particle accelerators of this kind in Germany, access is severely limited. In contrast, X-ray CT is more widespread at soil science institutes in Germany. The new approach thus facilitates research. "You can't normally look inside the soil. But this methodological innovation allows us to draw conclusions about where and how well carbon is enriched in soil depending on the pore system and organic material such as roots and litter," says Prof. Hans-Jörg Vogel, head of the Department of Soil System Science at the UFZ. This provides important information about processes in the soil and thus also about the consequences they have for the stabilisation and decomposition of carbon in soil.

Read on: https://www.sciencedaily.com/releases/2022/04/220421094101.htm

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