Plant Physiology - Musiyenko, M. M. 2001

Plants and the Biosphere. Ecological Cycles of Matter and Energy Flow
Plant and Biosphere. Water Cycle

Biogeochemical cycling refers to the repeated participation of various substances, or more precisely their constituent chemical elements, in processes occurring within the atmosphere, hydrosphere, lithosphere, including those layers that belong to the biosphere. The Circulation of Water between the World Ocean and dry land is a vital link in sustaining living organisms and a fundamental prerequisite for their interaction with inanimate matter (Fig. 217). The cyclical Movement of water carrying dissolved Mineral Substances naturally gave rise to living matter, and with it, to biological cycling. This is a continuous planetary process involving the cyclical and temporally as well as spatially uneven redistribution of matter, energy, and information, which repeatedly enter the constantly renewing ecosystems of the biosphere.

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Fig. 217. Water cycle

Biological cycling is the circular flow of matter among soil, plants, animals, and microorganisms, driven fundamentally by the absorption of minerals, their incorporation into plant Tissues, their transfer via trophic chains into heterotrophic organisms, and their subsequent return to the atmosphere or soil through the action of reducers.

The driving force behind the self-development, balance, and adaptive self-regulation of chemical element cycling and energy transformation in the biosphere is solar radiation, captured by plants through the unique process of Photosynthesis. Plant photosynthesis acts as the sole biogenerative link in biological cycling, serving as the primary producer of organic matter and the solar energy bound within it, whereas biodestruction encompasses the sum of all catabolic processes across various life forms on Earth. The photosynthetic conversion of sunlight into chemical energy marked a new epoch in The history of life and all geochemical processes on the globe. The enrichment of the atmosphere with molecular oxygen profoundly influenced the evolutionary trajectory toward The Development of aerobic organisms. The Emergence of the plant kingdom in both oceans and on land created a vast green shield for the planet, establishing a powerful biotransformer of energy, matter, and information flows in the biosphere. As a result, the reserves of living and dead organic matter steadily increased on Earth, while the planet's atmosphere gradually became enriched with oxygen alongside a simultaneous decrease in carbon dioxide concentration. This catalyzed the extensive proliferation of heterotrophs, which depend entirely on preformed organic matter originally produced by photoautotrophs.

For a considerable period in the history of life, the quantity of newly synthesized organic matter exceeded the portion transformed through Respiration and Fermentation within living organisms, leading to The formation of fossil fuel deposits on Earth. Alongside carbon, hydrogen, and oxygen, these deposits contained significant amounts of nitrogen, sulfur, phosphorus, and other mineral nutrient elements essential for plants. Gradually, The amount of organic matter newly created by phototrophs and the total volume of life on Earth reached an equilibrium with the consumption of organic matter through respiration, fermentation, and diverse oxidation processes, establishing a stabilized, balanced cycle of carbon and life on the planet.

Finally, the Earth's vegetation has formed and continues to form soils, enriching them with organic matter and humus—the foundation of soil fertility. Soil humus, as The most significant outcome of soil formation, also represents one of the final trophic stages bridging photosynthesized organic matter and the End products of its mineralization: water, carbon dioxide, ammonia, nitrates, iron oxides, hydrogen sulfide, silicon compounds, carbonates, phosphates, and sulfates. The soil cover and the World Ocean function as planetary sinks for diverse wastes. The breakdown of many organic and organomineral compounds is completed within the soil and the ocean, making them natural purification systems that cleanse the planet of numerous pollutants. While a fraction of matter may temporarily be removed from the cycle (settling at the bottom of water bodies or sinking deep into the Earth's crust), tectonic and geological processes eventually reintroduce these Materials into the cycle.

Thus, phytocenoses perform critical Functions in the biosphere that ensure the very existence of life. The first of these is the continuous process of biological accumulation, transformation, and redistribution of solar energy reaching the Earth via photosynthesis.

The second function is sustaining the global geochemical cycle of chemical elements on the planet, particularly biophiles such as carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, calcium, magnesium, potassium, copper, zinc, cobalt, iodine, and others.

These functions are mediated through the photosynthetic system that produces plant organic matter, which is utilized by herbivorous organisms. The zoobiomass of herbivores is subsequently consumed by various links in the trophic chains, including parasites, predators, scavengers, soil microflora, and microorganisms.