Phosphorus Cycle

Phosphorus (P) is an essential element for all life forms on Earth. Being a nonsubstitutable constituent of nucleoside phosphates (e.g., ADP [adenosine diphosphate], ATP [adenosine triphos-phate]) and nucleic acids (e.g., DNA [deoxyribo-nucleic acid], RNA [ribonucleic acid]), phosphorus plays a vital role in biochemical reactions involving energy transfer and transcription of genetic information in living organisms. Moreover, phosphorus has a generally low bioavailability and is a nutrient that commonly limits the productivity of terrestrial, freshwater, and marine ecosystems. In contrast with carbon, nitrogen, and sulfur, which can exist in several oxidation states, phosphorus does not take part in reduction-oxidation reactions and is predominantly present in the +5 oxidation state as phosphate (PO4-3). On a [Page 2170]centennial timescale, global transfer of phosphorus occurs unidirectionally from the terrestrial ...