**Photosynthesis in Global Cycle of Biospheric Carbon**

A.A. Ivlev

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52 Applied Photosynthesis - New Progress

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Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/62222

#### **Abstract**

A key role of photosynthesis as a regulator of global carbon cycle dynamics is considered. According to the suggested model, global natural carbon cycle is regard‐ ed as a transition of carbon from the oxidative state, presented by carbon dioxide, bicarbonate, and carbonate species, into the reduced state, presented by different biogenic forms, produced in photosynthesis and in the following transformations. Photosynthesis provides a conversion of oxidative forms into reductive ones. The reverse transition is realized via respiration of living organisms, via microbial and chemical oxidations, accompanying transformations of "living" matter after burial. Among them the oxidation of the buried organic carbon by means of thermochemical sulfate reduction in the subduction zone, where lithospheric plates collide, is most important. Photosynthesis is under the impact of the Earth crust processes. In particular, the lithospheric plates' movement exerts the impact on photosynthesis development via periodic injections of CO2 into "atmosphere–hydrosphere" system during the plates' collisions. The irregular lithospheric plates' movement generates orogenic cycles which consist of short-term orogenic period of active volcanism, magmatism, and mountain building and a long-term geosynclynal period of low volcanic activity and quiet development of Earth crust processes. The pulsating movement of plates affects the dynamics and development of photosynthesis, which in turn determines the periodici‐ ty of numerous processes in the nature, including climatic cycles, changes in the rate of biodiversity, irregular accumulation of organic matter in sediments, uneven strati‐ graphic oil distribution, sea level changes, etc. The redox carbon cycle is a selforganizing system due to negative feedback between CO2 assimilation and photorespiration of global photosynthesis in response to oxygen growth. It made carbon cycle to shift to ecological compensation point. In this point, the system becomes sensitive to separate plates' collisions that results in short-term climatic oscillations.

**Keywords:** photosynthesis, CO2 assimilation, photorespiration, "greenhouse" and "icehouse" periods, biodiversity, global carbon cycle, plate tectonics, orogenic and ge‐ osynclynal periods of orogenic cycle, sedimentary carbonates, burial organic carbon

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **1. Introduction**

Here we concentrate one's attention on the unusual role of photosynthesis as а regulator of global carbon cycle dynamics. It stems from a new model of global natural carbon cycle which, despite the popular point of view, regards carbon turnover not only as a simple transfer of the element between different geospheres and biospheres but also as a transition of carbon from the oxidative state, presented by carbon dioxide, bicarbonate, and carbonate species, into the reduced state, presented by different biogenic forms, produced in photosynthesis and in subsequent transformations. That is why we named natural carbon turnover like a redox cycle of biospheric carbon. It has two branches – oxidative and reductive (Figure 1). The transition from oxidative species into reductive ones occurs by means of photosynthesis. The reverse transition is realized via respiration of living organisms, via microbial and chemical oxida‐ tions, accompanying transformations of "living" matter after burial. Among them, there is an oxidation of the buried organic carbon by means of thermochemical sulfate reduction occur‐ ring in the subduction zone, where lithospheric plates collide. This process is a dominant contributor to the oxidative branch of cycle.

1 Photosynthesis 2 Respiration, oxidation of OM in subduction zone, and other oxidizing processes in the Earth crust

**Figure 1.** Putative global carbon cycle in nature. Oxidative and reductive branches. The points of carbon transition from the oxidative states to the reduced ones (in photosynthesis) and back (in sulfate reduction in subduction zone).

As early as 1926, a famous Russian geochemist V.I. Vernadsky put forward an idea on the interaction of biospheric and Earth crust processes [1]. This interpretation is as follows: photosynthesis developed under the impact of lithospheric plates' movement. The impact of lithospheric plates' movement on photosynthesis is transmitted via injections of CO2 arising in plate collisions with the participation of continental plates. In the course of these collisions under high temperatures arising in subduction zones, thermochemical sulfate reduction occurs resulting in the oxidation of sedimentary organic carbon. In the suggested scheme, the lithospheric plates' movement is an experimentally established fact, but the reason causing the movement is still arbitrary. A widespread hypothesis is that the movement results from magma convective motion which makes plates, covering magma surface, to move.

**1. Introduction**

54 Applied Photosynthesis - New Progress

contributor to the oxidative branch of cycle.

1 Photosynthesis

2 Respiration, oxidation of OM in subduction zone, and other oxidizing processes in the Earth crust

biogenic forms produced

**Figure 1.** Putative global carbon cycle in nature. Oxidative and reductive branches. The points of carbon transition from the oxidative states to the reduced ones (in photosynthesis) and back (in sulfate reduction in subduction zone).

**Reducing branch**

1 2

**Oxidative branch**

–, CO3 =)

(CO2, HCO3

in photosynthesis

Here we concentrate one's attention on the unusual role of photosynthesis as а regulator of global carbon cycle dynamics. It stems from a new model of global natural carbon cycle which, despite the popular point of view, regards carbon turnover not only as a simple transfer of the element between different geospheres and biospheres but also as a transition of carbon from the oxidative state, presented by carbon dioxide, bicarbonate, and carbonate species, into the reduced state, presented by different biogenic forms, produced in photosynthesis and in subsequent transformations. That is why we named natural carbon turnover like a redox cycle of biospheric carbon. It has two branches – oxidative and reductive (Figure 1). The transition from oxidative species into reductive ones occurs by means of photosynthesis. The reverse transition is realized via respiration of living organisms, via microbial and chemical oxida‐ tions, accompanying transformations of "living" matter after burial. Among them, there is an oxidation of the buried organic carbon by means of thermochemical sulfate reduction occur‐ ring in the subduction zone, where lithospheric plates collide. This process is a dominant

The carbon cycle spans different geospheres: atmosphere, hydrosphere, upper part of litho‐ sphere, and biosphere. Prior to the origin of photosynthesis, the atmosphere was anoxic [2, 3], and the reduced carbon was mainly methane formed by archaebacteria [4]. The redox carbon cycle changed in parallel with the expansion of photosynthesis destroying most of the methane in the atmosphere. As photosynthesis expanded, oxygen concentration in the atmosphere reached such a high level, at which its concentration stabilized. At this point, the oscillatory regime was established, and the perturbations of carbon cycle in the form of short-term (tens of thousands years) "cooling–warming" transitions have appeared, expressed as the glacial– interglacial oscillations. Carbon cycle characteristics became sensitive to separate plates' collisions and to other factors.

In this study, the author uses the previously proven claim that photosynthesis is accompanied by two photosynthetic carbon isotope effects in CO2 assimilation and in photorespiration having opposite signs [5]. It gave him the opportunity, basing on the actualism principle, to use the differences in carbon isotope composition of sedimentary organic matter and that of coeval carbonates, as a delicate tool to investigate 13C isotope discrimination in the past. It was used, in turn, to trace the climatic changes, the changes in the rate of biodiversity, to explain irregular accumulation of organic matter in sediments, uneven stratigraphic oil distribution, and many other phenomena.
