The cycling of nutrient elements is the crux of all ecological considerations because of their limited availability in the biosphere. The concept of growthlimiting nutrients has been discussed in Chapter 2 as well as the essential elements for all biological systems. It follows that continued utilization of one element as a nutrient by a given category of living organism would eventually tie up all of the available supply and that no further growth could occur once the supply was depleted. For example, if all of the carbon dioxide available to photosynthetic organisms was fixed (reduced) into an organic polymer form as the result of photosynthetic activity, no further photosynthesis could take place. The time estimated for such an occurrence on earth is a matter of days. If it were not for the continued renewal of the supply of carbon dioxide by the respiratory activities of other types of organisms, all life would stop soon after photosynthesis stopped and all of the available carbon would be fixed in the form of dead carcasses, leaves, wood, etc., to be preserved forever.
KeywordsNitrogen Fixation Heterotrophic Bacterium Pyruvic Acid Lipoic Acid Sulfur Cycle
Unable to display preview. Download preview PDF.