The utilization
of elements in carbon and mineral nutrition of plant is the conditions of
biological and geological cycles of substances. The accumulation of scattered
elements of the atmosphere, hydrosphere and soil crops in the form of the
living substance of autotrophic and heterotrophic organisms and the liberation
of those elements through their living activities as well as after death is
enormous in scale and importance, the biological cycle develop the part of the
geological cycle.
In the admission
of nutrient from the great geological cycle into the small biological cycle and
the reverse process does not possess the character of a closed cycle. The decomposition
of plant and animal organisms after death does not also proceed completely to
final product of mineralization, but it is accompanied by the new formation of
organic substance. In many cases of complex nature, it possesses a greater
resistance to decomposition than the original organic substance. The reverse of
organic carbon is these formations, including also the organic substances of
living organisms and their dead residues.
However, the
principal source of the carbon dioxide required by plants during photosynthesis
is the atmosphere, where the water content is approximately 0.03 percent or
about 0.57mg per 1 of air and its reserve, about 2.1 billion tons. When one
considers that land plants of the earth is fix annually, during photosynthesis
about 20,000 million tons of carbon or approximately 80,000 million tons of
water which then lead to the total carbon dioxide content of the atmosphere which
would be sufficient to last only for a few decades.
But it is a
well known fact that the water of the air is continually being replenished from
other reserves including the hydrosphere, the surface of which it mingles
freely with the atmosphere. In the air and in the waters of the earth, the
total amount of carbon dioxide which are available to land plant exceed 10
tons, which is sufficient to satisfy the carbon dioxide requirements of plants
for thousands of years. The most important source of replenishment of the carbon
dioxide of the atmosphere is the soil. During the cause of the day,
particularly during the hours of intensive photosynthesis, there may occur a
time when the carbon dioxide concentration in the air layers surrounding the
plant is lower than normal and this will result in a decrease in the intensity
of photosynthesis.
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