The carbon cycle

Green plants convert atmospheric carbon dioxide into carbohydrates by the process of photosynthesis. These carbohydrates in the form of sugars and starches are formed in the green leaves of plants, and are distributed to all parts of the plant above and below ground level by sap flow. As the plants mature and die, these carbon compounds are used as food by animals and other soil biota. This carbon is subsequently made available in the soil as humus, compost, and chemicals such as humates, fulvates and carbonic acid. These chemicals in turn can react with inorganic chemicals in the soil, making them available to plants for uptake through their roots. As this carbon ends up in the food web, it is converted back into gaseous carbon (as carbon dioxide and methane) and returned to the atmosphere to begin the cycle again (Figure 9).

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