During the development of methods for modeling the production process, the rate
of photosynthesis is determined through empirical dependences (light and carbon
dioxide curves of photosynthesis), semi-empirical models in which the diffusion of
carbon dioxide (CO
2
) molecules is described by the laws of biophysics, while the
photosynthetic cycle is described by the laws of biochemistry.
When modeling the production process, it is necessary to describe the
photosynthesis in the plant's green organs, the absorption of mineral substances by
roots, the "counter" transport of water, carbohydrates and mineral elements, the
biosynthesis of amino acids, proteins and high molecular weight carbohydrates, the
growth of various plant organs and development, which is understood as a change in
certain stages of the ontogenesis or as a change in the phenophase. Photosynthesis is
the primary link in this chain: sugars are formed from carbon dioxide and water under
the action of sunlight in chloroplasts in the presence of chlorophyll which acts as a
catalyst:
6СО2 + 6Н2О + hv → C
6
H
I2
O
6
+ 6О
2
↑ + chem. energy,
(3)
The process of photosynthesis is divided into two main phases. In the first of these
(photochemical), water under the influence of light is split into hydrogen and oxygen,
and in the second one (biochemical) СО
2
is combined with hydrogen. In the modeling
of photosynthesis, the main task is to describe the diffusion of CO
2
into the inner tissues
of the leaf and its transition into a solution, the absorption of solar radiation by the
leaves and its photosynthetic active radiation (PAR), the actual synthesis of sugars in
the process of carboxylation. The dependence of these processes on the internal factors
of the state of plants is also taken into account: the water content of their tissues, their
temperature, the concentration of chloroplasts in the leaves, stems and ears.
The diffusion of gaseous CO
2
into the intercellular spaces occurs mainly through
the stomata, the degree of opening of which is influenced by the incoming radiation
and the water potential of the leaf. This ensures the connection of photosynthesis
intensity with the water regime. The leaf temperature is also affected by radiation and
water regimes. This, in particular, explains the midday depression of photosynthesis.
At intensive transpiration, there is a partial dehydration of tissues, the stomata close,
the temperature of leaves increases, the rate of photosynthesis decreases.
Plants, absorbing CO
2
from the atmosphere by means of leaves and taking up
water from the soil by the root system, elaborate organic compounds in the form of
assimilates during photosynthesis under the influence of solar radiation energy. At the
same time, there occurs transpiration which is responsible for providing plants with
water and elements of mineral nutrition and for regulating the thermal regime of plants.
Depending on the intensity of PAR, water and temperature regimes, wind speed, CO
2
concentration in the air, soil fertility and the specific characteristics of the plants, the
process of photosynthesis can run at a higher or lower rate.
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