Computed tomography has shown that soil carbon is stored mainly in a network of pores

(ORDO NEWS) — The soil cover of the Earth is a huge store of carbon, it contains even more of it than in all the plants of our planet combined. In their new study, soil scientists have found that most of this key element for life is stored precisely in the intricacies of small soil pores.

Soil is a dynamic and complex mixture that combines mineral components, living organisms and their metabolic products.

The soil is characterized by special patterns of development, it plays a huge role in the life of the Earth’s biosphere and climate change on our planet. Unfortunately, the importance of soils for global warming is often neglected.

But the soil is still a colossal reservoir of carbon, firstly, a chemical element that underlies all living things, and secondly, a component of a greenhouse gas – carbon dioxide.

Thin, only occasionally reaching a thickness of one or two meters, the soil cover stores more carbon than all the vegetation of the biosphere.

If we consider long-term changes in gas exchange with the participation of the soil, then the behavior of this carbon storage will be quite complex.

It is influenced, on the one hand, by the amount of carbon entering the soil from the atmosphere, which is associated with root growth, various mixing processes (including plowing and worm activity), infiltration of organic solutions, and so on.

On the other hand, the balance of carbon depends on the stabilization or decomposition of organic matter by soil bacteria and fungi. The predominance of the processes of storage of carbon compounds or, on the contrary, their destruction depends mainly on the fine structure of the soil.

And that, in turn, is determined by the size of the pores, which form many connected channels with a huge total surface area. It is thanks to these “tangled corridors” that air, water and nutrients dissolved in it move through the soil.

Computed tomography has shown that soil carbon is stored mainly in a network of pores
Fine structure of the three types of soils considered in the work. Pores are shown in yellow

“The carbon stored in plant debris and humus cannot be used if bacteria or fungal hyphae are larger than the soil pores in which it is stored,” says Dr. Steffen Schlüter, soil physicist at the Helmholtz (Germany). It was he who led the team of authors of a new article in the journal Nature Communications .

Moreover, if these pores are constantly filled with water and, as a result, deprived of incoming oxygen (for example, in peat soils preserved in their natural form), then it will be difficult for bacteria to use the carbon present in them.

“One of the decisive factors that determines exactly where carbon will be stored in the soil is the spatial distribution of the pores,” continues Schlüter.

So far, soil scientists have not been able to directly study the distribution of carbon in soil pores with a diameter of millimeters and micrometers. However, Schlueter and his colleagues applied a new methodology.

Their approach is based on the use of a specific dye, osmium tetroxide , which makes it possible to trace the fate of organic matter in the soil.

This compound reacts with double bonds between carbon atoms, after which its distribution is visualized using X-ray computed tomography. By obtaining an image before and after staining with osmium tetroxide, scientists can directly learn about the distribution of organic matter in a soil sample.

As an example, the authors of the work tested their new method on soils of various kinds. Among them was chernozem with a small amount of annual precipitation, having a fine structure of luvisol (contains a horizon of accumulation of active clay) with seasonal waterlogging, as well as constantly moist gleyzem.

In all cases, in the immediate vicinity of the pores (at a distance of 50 to 10 micrometers), there was noticeably less carbon than in the rest of the soil: the reason is that even at a small distance from the pores, the activity of microorganisms noticeably decreases.

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