TAILIEUCHUNG - From Individuals to Ecosystems 4th Edition - Chapter 18

Chapter 18 The Flux of Matter through Ecosystems Introduction Chemical elements and compounds are vital for the processes of life. Living organisms expend energy to extract chemicals from their environment, they hold on to them and use them for a period, then lose them again. | Chapter 18 The Flux of Matter through Ecosystems Introduction Chemical elements and compounds are vital for the processes of life. Living organisms expend energy to extract chemicals from their environment they hold on to them and use them for a period then lose them again. Thus the activities of organisms profoundly influence the patterns of flux of chemical matter in the biosphere. Physiological ecologists focus their attention on how individual organisms obtain and use the chemicals they need see Chapter 3 . However in this chapter as in the last we change the emphasis and consider the ways in which the biota on an area of land or within a volume of water accumulates transforms and moves matter between the various components of the ecosystem. The area that we choose may be that of the whole globe a continent a river catchment or simply a square meter. Relationships between energy flux and nutrient cycling The great bulk of living matter in any community is water. The rest is made up mainly of carbon compounds 95 or more and this is the form in which energy is accumulated and stored. The energy is ultimately dissipated when the carbon compounds are oxidized to carbon dioxide CO2 by the metabolism of living tissue or of its decomposers. Although we consider the fluxes of energy and carbon in different chapters the two are intimately bound together in all biological systems. Carbon enters the trophic structure of a community when a simple molecule CO2 is taken up in photosynthesis. If it becomes incorporated in net primary productivity it is available for consumption as part of a molecule of sugar fat protein or very often cellulose. It follows exactly the same route as energy being successively consumed defecated assimilated and perhaps incorporated into secondary productivity somewhere within one energy cannot be cycled and reused matter can . of the trophic compartments. When the high-energy molecule in which the carbon is resident is finally used to

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