الفهرس 
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Abstract
Maintenance of Life in the biosphere requires the regeneration of a array of nutrient elements required for growth,reproduction and replacement, of organism. The recycling rates of these elements limit primary production and so regulate biotic eneray flow, a positive feedback Loop inherent in the structure of the ecosystem since the energy flow produces nutrient cycles, which lead to greater energy flow (Webester et al 1975; Mitchell et ab 1975).