Organophosphorus, such as inositol phosphate (IP), may serve as a source of orthophosphate (OP) in freshwater. The contribution from recalcitrant organic-P to the OP pool has been overlooked due to the lack of tools capable of accurately measuring OP production from organic-P. However, in the absence of OP, specialized enzymes are produced by competent aquatic microorganisms to get OP from organic-P forms. This study aimed to quantify OP production from phytic acid, a surrogate for recalcitrant organic-P, to assess the contribution of recalcitrant P forms to the total OP pool that fuels algal blooms in freshwaters. A fluorescence probe serving as a substrate analog for phytic acid was used to measure the enzymatic activity required for IP mineralization to quantify OP production from IP accurately. Though IP mineralization rates were relatively low, results highlighted the importance of considering recalcitrant organic-P as a viable source for OP.
