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Phosphate Availability and Interactions with Calcium and Iron

Iron-bound phosphate represents less than 1 % of total phosphate. A major fraction is bound to calcium (e.g., calcium hydroxy apatites). Mobilisation of calcium bound phosphorus is stimulated by protons and organic acids formed by fermentation processes; this might play a role in reducing sediments (Stal et al., 1996). However, in recent experiments it has been shown that phosphate release was only slightly stimulated by amending anoxic sediment slurries with glucose. The most probable explanation for this result was that protons and organic acids produced during fermentation were quickly consumed by sulfate-reducing bacteria (Schaub & Stal, Extended Report, Vol. I, p. 307). Organic phosphate was a major fraction in the vegetated site (57 %) and less important at the non-vegetated site (7 %). Hence, plant biomass and detritus represent a major temporal sink for phosphorus and we have studied remineralisation of organic phosphorus and the importance of bacterial phosphatases in this process. Interestingly, alkaline phosphatase activities were very low at the non-vegetated site and higher, albeit patchily distributed, at the vegetated site. On average per cm-3, vegetated sites yielded 4 to 5 times more culturable viable bacteria showing phosphatase activity than non-vegetated sites (Donnelly et al., 1998, Progress Report p. 51).


Rutger DE WIT
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