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CH3041
‘P’ SUBCYCLES
Biological cycle:
• Plants can absorb only one form of soluble
phosphate oxoanion : dihydrogen phosphate
•        H2PO4-  D  H+ + HPO42- D H+ + PO43
Ca3(PO4)2(soil)  + H+(out, roots) ® 3Ca2+ + 2H2(PO4)-(in, roots)
• Most of the solubilized ‘P’ that enters the
ocean comes from biological decay+ human
fertilisers & polyphosphate
detergents eg. P3O105-
R
P
     algal biomass = C106H263O110N16P1                           (Redfield)
• Some dead biomass ‘P’ is returned to rock
by deep ocean sedimentation as Ca5(PO4)3 
Water based cycle:
106CO2 + 16NO3- + H2PO4- +122H2O + 17H+ D algae. + 138O2