Factbox 2.
A Prerequisite For All Life On Earth

By Professor Nils Nykvist

The organic substances that are vital for all life on earth are formed through the chemical reaction that takes place in green plants, when energy from the sunlight forms energy-rich compounds from water and carbon dioxide. And this chemical reaction is known as photosynthesis.

One of the main reasons for the large differences in plant production of the world is the availability of water in the soil. Locally, however, there is a decrease in soil water during the daytime when the plant’s photosynthesis dominates, and an increase during the night, due to plant respiration.

The content of carbon dioxide in the air is, on the other hand, globally relatively constant.

Just as water and light within certain limits can increase photosynthesis, an increase in the content of carbon dioxide in the air can also lead to higher crop production, and is used in some greenhouse cultivations. The increase in atmospheric carbon dioxide that has occurred during the past century because of the great burning of fossil fuels and the cutting down of forests could theoretically also lead to greater plant production, but no proof of this has yet been found.

During photosynthesis, oxygen is formed in addition to organic matter. The formation of one kilogram of the sugar glucose as an example of organic matter can be written as follows:

1.5 kg carbon dioxide (CO2) + 0.6 kg of water (H2O) + energy → 1.0 kg carbohydrate (C6H12O6) + 1.1 kg of oxygen (O2)

By the photosynthesis of the plants, energy from the sun is bound and the reaction goes from left to right. When the organic matter is oxidized by oxygen, the reaction goes in the opposite direction and energy is released.

This reaction is necessary for a continuation of the plant’s photosynthesis, since carbon, water, and nutrients that the plants have taken up would otherwise accumulate in the organic matter and no longer be available to the plants.

The solar energy bound into the organic matter is used by animals and decomposing organisms, or released as heat when organic matter burns.

The organisms involved in the decomposition processes are essentially different forms of bacteria, fungi, and small animals that live in the soil.

Man’s direct consumption of organic matter is relatively small, but can, by fire and deterioration of soil and vegetation, indirectly be very high.

Globally, there is a balance between formation and decomposition of organic matter.

Locally, however, organic matter can accumulate in soils where the content of oxygen is not sufficient for decomposition of the biomass produced from the wetland plants. This is the case when the soil is water-saturated and the flow of air limited because the soil pores are filled with water.

As long as the supply of oxygen into the soil is limited, organic matters grow in thickness, leading to an increase of the distance to the groundwater. When this distance increases, more and more oxygen can penetrate into the soil.

Sooner or later, there is a balance between production and decomposition of organic matter and plants other than wetland plants can colonize the area. When the flow of air into the soil is improved by draining, the thickness of the organic layers can decrease so much that the soil surface sinks several decimetres.

Very thick layers of organic matter are formed when land subsides into the sea and the supply of oxygen is reduced.

Examples of this are the large stocks of coal and lignite found in many countries. The solar energy stored in these organic layers, formed several million years ago, is now the energy that we use in the form of fossil fuels.

Return from this page on Photosynthesis to The Soil Degradation Series

Return from this page on Photosynthesis to All Recycling Facts Homepage

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