CARBON (C) 12.011 Atomic Weight

(Primary Nutrient)

Carbon is the one element required in largest amounts by organisms.  It is a common constituent of all organic matter, and is involved in virtually all life processes, as it is part of the DNA Molecule.  The Carbon Cycle can be described as a “biocycle” making possible the continuity of all life on earth.  Even though Carbon is the ‘number one’ building block for all life, it is rarely mentioned as a plant nutrient.  Carbon is taken in through the plant’s leaves directly from the air as carbon dioxide (CO₂).

Carbon as carbon dioxide makes up 0.03% of the earth’s atmosphere, and it constitutes 0.025 percent of the earth’s crust.   The lack of soil organic Carbon is a sure sign of a lack of organic matter in the form of humus, which is food for bacteria. There are more than a million known Carbon compounds, many thousands of which are vital to organic and life processes.

When too much Nitrogen is added to the soil, it induces a carbohydrate deficiency and reduces bacterial populations. Carbohydrates are the sugar, (Carbon, Hydrogen, Oxygen), energy source for bacterial populations to thrive. Bacteria are most abundant at a soil Carbon to Nitrogen ratio of 30 to 1.  Added Nitrogen induces a sugar deficiency that reduces bacterial competition to fungi root diseases and nematodes.

Carbon leaves the Earth’s soils and goes to the atmosphere as CO₂ in a constant cycle known as the Carbon Cycle. Vegetation collects carbon dioxide from the air, releases the oxygen (O₂) and returns the carbon (C) to the earth.

All photosynthetic forms can reduce atmospheric CO₂ but not all can use CO₂ as their sole source of Carbon.  In the non-sulfur purple bacteria, organic substances such as acetate act as Hydrogen donors for CO₂ reduction.  In contrast, other microbes, such as nitrifying bacteria, utilize inorganic substances exclusively and must therefore use atmospheric CO₂ as their only Carbon source.

Most microbial forms oxidize organic materials, which serve not only as substrates in energy yielding reactions but also as sources of carbon for nutrition.  The range of organic compounds from which carbon is extracted by organisms is endless. Microorganisms, as a group, are especially versatile in this respect, in fact, for every naturally occurring organic material; there is a microbe capable of decomposing it.  This is the reason why microorganisms play such a vital role in the geochemical cycling of the elements, especially carbon and nitrogen.

Carbohydrates are among the most readily available sources of carbon for microorganisms.  Monosaccharides, (simple sugars), are widely used but alcohols, such a mannitol and glycerol are good sources too, especially for fungi and actinomycetes. Amino acids are readily used as Carbon sources by most microorganisms while some can utilize fatty acids. Hydrocarbons, (oils), can serve as a carbon source for a few bacteria of the genus corynebacterium, mycobacterium and pseudomoas.

Utilization of compounds such a lignin is quite extensive under aerobic (O₂) conditions, but when Oxygen is limited such compounds are not decomposed.  Instead they accumulate, for example, as peat or coal.  The major lignin decomposers are Fungi, Pseudomonas and Actinomycetes.