Pedosphere Explained
The pedosphere – Earth’s soil or earth – is essential for plant growth and therefore for life itself

The Pedosphere: Earth’s Soil & Earth

The “pedosphere”, the uppermost level of the lithosphere, is the layer of soil, dust, small stones, sand, silt and other regolith, which covers the Earth’s land masses. Soil may not be exciting, but it is essential, since without it there’d be no trees or plants and therefore no life. For more, see our in-depth article: Why is Soil So Important to the Planet?

As well as helping to feed the planet – a vital role, as food supplies try to cope with a global population approaching 10 billion – the pedosphere also has an important influence on Earth’s climate system, due to the storage of carbon dioxide in its forests and biomass and its role in the carbon cycle.

Soil includes a wide variety of organic material, such as humus, leaf matter, plant debris and other partially decomposed remains of animals and animal waste. It also contains a host of microbes and microorganisms, such as green algae, various fungi, bacteria and lichens. Estimates of the number of species present in one gram of soil vary between 50,000 and one million. 1 As it forms and develops, the soil’s profile deepens and develops characteristic layers, called ‘horizons’.

Originally seen as simply a base for vegetation, the pedosphere is now viewed as the main transit area for biogeochemical substances as they move between the biotic and abiotic realms of the Earth. It takes in CO2 from the atmosphere, water from the hydrosphere, stores permafrost carbon for the cryosphere, is home to the biomass and decomposers of the biosphere, and is the starting point for soil sediments as they sink down into the lithosphere. Indeed, one might call it the foundation of terrestrial life on Earth. 2

What Are Soil Horizons?
Dig down deep into any soil and you will discover it has different layers. These layers are called horizons (O, A, E, B, C, R). Put the horizons together, and they form a soil profile, which tells a story about the life of the soil. Photo: © Courtesy of Hridith Sudev Nambiar & Wilsonbiggs

What Is Pedology, Edaphology And Pedometrics?

They are all soil sciences. Soil science embraces at least four separate areas. (A) Pedology, which includes pedogenesis (soil formation) and soil morphology (form and structure); (B) Edaphology, which deals with the way soils interact with plants, fungi, lichens, bacteria and other living things; (C) Pedometrics, the statistical and mathematical analysis of soil data. 3 4 (D) Environmental soil science, which studies aspects of the vadose zone (the soil layer which lies between the earth surface and the groundwater table), soil degradation and contamination, treatment of wastewater, soil erosion control, restoration of wetlands, and nutrient management, among many other subjects. It also examines soil in the context of land use and climate change.

The study of the pedosphere also overlaps with other geosciences, such as biology, meteorology, climatology, ecology, hydrology, oceanography, geomorphology and geology, among other earth sciences

With growing pressure on food supply and agriculture – in light of the expected 3.5 billion population increase by 2100 – as well as alarm over global warming and deforestation, the collection of soil data in respect of temperature, moisture, and other pedological metrics, is becoming an important source of data about many aspects of Planet Earth.

For example, agricultural scientists and botanists use the data to better understand the potential for plant growth; hydrologists use the information to analyze potential sedimentation in water bodies; meteorologists use it in computerized climate models, as the pedosphere affects humidity and temperature; climatologists study soil data to estimate carbon stocks in the rainforest and the taiga permafrost; biologists use it to gauge its impact on biodiversity; while paleoclimatologists study the soil in order to reconstruct historical climates.

Why Is The Pedosphere Important?

Firstly, because the pedosphere forms a major part of Earth’s critical zone – the diverse, near-surface environment which hosts an intricate interplay between rocks, soil, water, oxygen, carbon dioxide, and living organisms, that determines the availability of life-sustaining resources and sustains nearly all terrestrial life. 5

For example, the pedosphere gives life to plants by providing an environment for them to establish their roots. Once established in the soil, plants and trees are connected to all the important biogeochemical pathways, such as the nitrogen cycle, the oxygen cycle, the phosphorus cycle and the sulfur cycle, among several others. Plants are vital for life and our long-term survival. Not least because they enable large-scale food production, farming and animal feed. 6

The pedosphere is also important because it supports a huge variety of “decomposers” – tiny organisms such as earthworms, bacteria and fungi – that break down plant litter, dead trees, animal waste and animal remains, thus helping to recycle nutrients including oxygen and carbon. These microorganisms burrow through the soil creating passageways for water, gases and other nutrients, thus maintaining soil and plant health.

Thirdly, the pedosphere plays a vital role in the water cycle. It acts as a filter system for groundwater, by absorbing anthropogenic pollutants like heavy metals, as well as excessive nutrients. What’s more, by soaking up rainfall it minimizes damaging run-off and retains moisture for plants to recycle via their roots for photosynthesis as well as transpiration.

Fourthly, due to its forest and plant cover – notably in tropical forests like the Amazon Rainforest – the pedosphere constitutes the largest carbon reservoir on land, holding 3 times more carbon than the atmosphere. This is because tropical forests receive more rain and sun than anywhere else on earth. With higher temperature and rainfall, and longer growing seasons, vegetation grows extremely fast, leading to the production of as much as 800 grams of carbon per square metre per year. 7 See also: Is More CO2 Good for Plants?

What Are The Risks To The Pedosphere?

The main risks to the pedosphere are soil erosion, degradation, and fertility.

  • One of the biggest dangers for the pedosphere is soil erosion. Rising demand for food and other agricultural commodities leads to deforestation and the expansion of croplands and pasture. (See for example: Deforestation in the Amazon Rainforest.) This switch away from natural vegetation often leads to soil erosion, as many of these new crops (like palm oil, soybean, coffee, cotton and wheat) are unable to hold on to soil like the original plants – one reason why half of all the topsoil on the planet has been lost in the last 150 years. 8 Soil erosion also leads to increased sedimentation and pollution in waterways, causing declines in marine stocks, water quality and biodiversity.
  • Soil degradation is another problem. According to one study, 22 percent of Earth’s croplands, pastures and forests has been degraded in one way or another. As a result, between 12 and 13.4 percent of global agricultural production is estimated to have been lost during the period 1950-20002. 9. As well as this, degraded soil also compromises biodiversity.
  • Another issue is soil fertility. Intensive cultivation can deplete vital soil nutrients such as nitrogen, phosphorus and potassium. If you deplete the soil of these key nutrients, plant growth is reduced. Intensive farming typically involves the use of agro-chemicals including chemical pesticides, fertilizers, insecticides, herbicides, and acaracides. Although yields have increased as a result, researchers have found that these chemicals are used they not only destroy their intended targets such as pests, weeds and parasites but also contaminate the food products. In addition, such chemicals tend to alter soil composition and thus disrupt the balance of microorganisms in the soil. This results in the growth of harmful bacteria at the expense of beneficial kinds.
  • As a result, natural animal habitats have been heavily affected, which impacts on the local ecosystem including the crops. In addition, the use of chemical fertilizers and herbicides contaminates water bodies like streams, rivers and lakes, further compromising the environment. Fertilizer nutrients, for example, are the main cause of eutrophication in the water system. 10

What Effect Does The Pedosphere Have On Climate Change?

The pedosphere’s most important effect on climate change is its storage of carbon in its trees and biomass. The Amazon Rainforest alone, for example, is estimated to remove a net total of 300 million tonnes of CO2 from the atmosphere every year. 11

The World Resources Institute claims that tropical rainforests can provide 23 percent of the cost-effective climate change mitigation needed up to 2030, to meet goals set in the Paris Climate Agreement. 12

Unfortunately, the huge Arctic fires that swept across Siberia, Canada and Alaska in 2019, showed the impact of rising temperatures on forest vegetation. In one month alone (June 2019), the northern fires emitted as much carbon dioxide (CO2) as the entire country of Sweden does in a whole year. 13

In the Southern Hemisphere, the Australian bushfires of 2019-2020 released more than twice the annual CO2 emissions of Australia, in a matter of months.

According to one study, elevated temperatures may also have an adverse effect on photosynthesis (Doughty and Goulden, 2008), or else leaves may respond indirectly to the accompanying loss of water vapor pressure by closing stomata (Lloyd and Farquhar, 2008). This refutes the idea that more CO2 in the atmosphere from global warming automatically leads to increased plant growth. 14

Land cover, the type of vegetation or other material covering the Earth’s surface has another small influence on climate, by virtue of its albedo effect – its capacity to reflect sunlight back into space, thus cooling the planet. Vegetation invariably has a lower reflective capacity than soil, and a much lower albedo than deserts.

For more about the timeline of Earth and its pedosphere, as well as a historical summary of global warming, please see: History of Earth in One Year (Cosmic Calendar).

References

  1. “Computational improvements reveal great bacterial diversity and high metal toxicity in soil” (PDF). Science. 309 (5739): 1387–90. Gans, Jason; Wolinsky, Murray & Dunbar, John (2005). []
  2. Skinner, B.J. & Porter, S.C.: Physical Geology. The Earth: Inside and Out, 1987, John Wiley & Sons. []
  3. “Soil Genesis and Classification”, 4th ed. Iowa State Univ. Press, Ames. Stanley W. Buol, F.D. Hole, R.W. McCracken. 1997. []
  4. “The Definition of Pedometrics” (PDF). Gerard Heuvelink (December 2003). Pedometron. International Working Group on Pedometrics – Provisional Commission on Pedometrics of the International Union of Soil Sciences. []
  5. “Basic Research Opportunities in Earth Science.” Executive Summary. National Research Council, 2001. []
  6. “Why are plants important?” Eleanor Clark. The Woodland Trust. []
  7. Biogeochemistry: an analysis of global change (3rd ed.). Oxford: Academic Press. ISBN 978 – 0123858740. Schlesinger, W.H..; Bernhardt, E.S. (2013). []
  8. “Soil Erosion and Degradation.” WWF. 2019. []
  9. Soil degradation: a global problem endangering sustainable development.” Chen Jie, Chen Jing-zhang, Tan Man-zhi, Gong Zi-tong. Journal of Geographical Sciences. April 2002, Volume 12, Issue 2, pp 243–252. []
  10.  “What is Intensive Farming?” Conserve Energy Future. []
  11. Size and frequency of natural forest disturbances and the Amazon forest carbon balance.” Fernando D.B. Espirito-Santo et al; Nature Communications. Volume 5, Article number: 3434 (2014). []
  12. “By the Numbers: The Value of Tropical Forests in the Climate Change Equation.” World Resources Institute. David Gibbs Nancy Harris, Frances Seymour. October 04, 2018. []
  13. “Arctic wildfires emitted as much CO2 in June as Sweden does in a year.” World Meteorological Organization. July 12, 2019. []
  14. “Evidence that Tropical Forest Photosynthesis is Not Directly Limited by High Temperatures.” Smith, M.; Taylor, T.; Van Haren, J. L. M.; Rosolem, R.; Restrepo-Coupe, N.; Wu, J.; Oliveira Junior, R. C.; Silva, R. D.; De Araujo, A. C.; Camargo, P. B. D.; Huxman, T. E.; Saleska, S. R. American Geophysical Union, abstract #B42A-07. December 2016. Bibcode: 2016AGUFM.B42A..07S []
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