Plant Physiology - Musienko, M. M. 2001

Photosynthesis: Physiological, Biochemical and Ecological Aspects
Production Process and Photosynthesis

Defining the ecological framework and the potential for enhancing agrocenosis productivity by increasing the utilization coefficient of solar radiation is one of the paramount challenges in modern crop production. The Physiological principles of programming the production process involve The formation of cenoses featuring optimal parameters for leaf area, net photosynthetic productivity, photosynthetic potential, and the efficiency of the assimilating surface.

Ultimate photosynthetic productivity results from the coordinated activity of Photosynthetic Systems and photosynthetic units within the thylakoid membranes, METABOLISM/14.html">Chloroplasts, and leaf mesophyll of phytocenosis plants. Characterizing an "ideal" photosynthetic system, A.O. Nichiporovich (1982) posited that Photosynthesis achieves peak energetic efficiency when the reduction of one g·mole of CO₂ (44 g or 6.2×10²³ molecules) requires eight quanta or eight einsteins of chlorophyll-absorbed PAR (8×6.02×10²³ hv).

The maximum intensity of PAR striking 1 dm² of leaf surface equals 15.07 kJ×dm^-2×h^-1, while the amount absorbed by active leaf chlorophyll is approximately 12.5 kJ×dm^-2×h^-1. Given this, and taking into account that one einstein of PAR corresponds to 209.35 kJ, it can be determined that a PAR intensity of 12.56 kJ×dm^-2×h^-1 corresponds to the following PAR quantum flux density:

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Under an eight-quantum process, the photosynthetic system should consequently assimilate:

or carry out photosynthesis with an intensity of:

In contrast to the "ideal" system, real leaves functioning as photosynthetic Organs contain only 3–7 mg of chlorophyll, corresponding to 4.0–5.5×10⁹ chloroplasts and 0.8–1.2×10¹⁶ reaction centers per 1 dm².

This enables true photosynthesis with an eight-quantum cost of 20–40 mg CO₂×dm^-2×h^-1, and gas-exchange-observed values of 15–30 mg, though only at low PAR intensities. Modern crop production utilizes photosynthesis with a PAR storage efficiency coefficient in the harvested yield at the level of 0.1–0.5% (rarely 1–2%). The intensification of crop production since 2000 aims to elevate this level to 3–5% of PAR, accompanied by a reduction in crop acreage (calculated per capita, it will decrease in developed countries from 0.6–0.8 to 0.2–0.3 ha).

The transition from extensive to intensive crop production Methods has unfortunately spawned a series of negative trends, which the applied aspects of photosynthesis and the production process are designed to resolve. Chief among these negative trends is the surge in resource and energy expenditures per unit of crop yield. It is estimated that doubling crop yields requires a 20-to-30-fold increase in resource and energy inputs. Agricultural production as a whole is becoming a major driver of chemical and biogenic pollution. Furthermore, rising yields are accompanied by a decline in crop quality. Establishing the physiological foundations for quality management is therefore critical, primarily through optimizing and balancing the processes of growth, photosynthesis, and the accumulation of economically valuable products.

Understanding the fundamental mechanisms of the photosynthetic process itself, along with the pathways of transformation and subsequent utilization of assimilated energy and newly synthesized organic matter within the plant Organism, forms the basis for advancing The Theory of the production process and developing systems for its optimization.