Elemental cycles organisms

Table 3-5 Elemental cycles and selected important transformations in which organisms play roles...

As reactive P is transported through the terrestrial system, it is assimilated into plants and subsequently into the rest of the biosphere (2). Although many elements are required for plant life, in many ecosystems P is the least available and, therefore, limits overall primary production (Schindler, 1977 Smith et al., 1986). Thus, in many instances the availability of P influences or controls the cycling of other bioactive elements. When organisms die, the organic P compounds decompose and the P is released back into the soil-water system. This cycle of uptake and release may be repeated numerous times as P makes its way to the oceans. 

Not surprisingly, only about 20 of the chemical elements found on Earth are used by living organisms (Chapters 3 and 8). Most of them are common elements. Rare elements are used, if at all, only at extremely low concentrations for specialized functions. An example of the latter is the use of molybdenum as an essential component of nitrogenase, the enzyme that catalyzes the fixation of elemental dinitrogen. Because they are composed of common elements, living organisms exert their most profound effects on the cycles of those elements. 

The most noteworthy multistage element cycles in which bacteria play important roles are the nitrogen and sulfur redox cycles. The fixation of nitrogen is a reductive process that provides organisms with nitrogen in a form usable for the synthesis of amino acids, nucleic acids, and other cell constituents. In essence, the overall conversion to the key intermediate, ammonia, can be represented as ... 

Not only do microorganisms have a profound influence on the concentration of elements in the atmospheric, aquatic and terrestrial environments (Lovelock, 1979), but the concentration and chemical speciation of these elements predicates which organisms can compete and survive within a given environment. Therefore, the cycling and mobility of trace elements will be linked to the cycling of bulk elements and correlations to the various bulk element cycles can be postulated. 

Fungal involvement in element cycling at local and global scales has important implications for living organisms, plant production and... 

---