Journal d'écosystème et d'écographie

Abstrait

Global Photosynthesis and its Regulatory Role in Natural Carbon Cycle

 Alexander A. Ivlev

 Main features of global photosynthesis operating in global carbon cycle are considered. Global photosynthesis has all the basic features of normal photosynthesis of C3 type, excepting those that characterize ontogenetic changes. They include: the existence reciprocal processes assimilation and photorespiration, the possession of the key enzyme Rubisco having carboxylase/oxygenase activity, the existence of oscillatory mechanism switching over assimilation to photorespiration and back, carbon isotope fractionation in CO2 assimilation and photorespiration with opposite signs of isotope effects and some others. Considering these features of global photosynthesis, its functioning in global carbon cycle is analyzed. The photosynthetic mechanism forming carbon isotope composition of “living matter” and sedimentary organic matter is suggested. It is shown that environmental conditions of photosynthesis in the location plays a dominant role in forming carbon isotope composition of the above objects. The difference in environmental conditions determines facial isotopic shifts. The analysis of natural isotopic data confirms this conclusion. It allows saying that carbon isotopic difference between oils and organic matter is inherited from the difference between lipid fraction and other part of biomass of “living matter” that was the source of initial biogenic material. It is shown that global photosynthesis performs in global carbon cycle a regulatory role ensuring cycle’s movement to the ecological compensation point. The regulatory role is based on the ability of photosynthesizing organisms to respond to the increased oxygen concentration in the course of evolution by reducing assimilation and increasing photorespiration. The achievement of ecological compensation point means that oxygen atmosphere was stabilized and further accumulation of organic matter in the Earth’s crust stopped.