Mechanisms of enhanced inorganic phosphorus accumulation by periphyton in paddy fields as affected by calcium and ferrous ions

The effect of periphyton propagation in paddy fields on phosphorus biogeochemical cycling has received little attention. In this phytotron study, inorganic phosphorus (Pi) accumulation by periphyton was investigated for varying inputs of calcium [Ca(II)] or ferrous‑iron [Fe(II)], and lighting conditions. Results indicated that additions of Ca(II) or Fe(II) enhanced abiotic accumulation of Pi by up to 16 times, and decreased solution Pi concentration by up to 50%, especially under light condition. The enhanced Pi accumulation into periphyton intensified with increasing Pi concentration, and Pi accumulation showed a positive linear relationship with Ca or Fe accumulation. Abiotic accumulation of Pi induced by Ca(II) was mainly through Ca-phosphate precipitation, and co-precipitation of P with carbonates at pH>8. Accumulation with added Fe(II) was mainly considered to be through Fe(III) phosphate precipitation coupled with adsorption of Pi by ferric hydroxides. Moreover, Fe(II) was more effective than Ca(II) in promoting abiotic accumulation of Pi by periphyton. Our results indicate the potential for controlling environmental factors to enhance the role of periphyton in biogeochemical cycling and P-use efficiency in paddy rice fields and to reduce P discharged to neighboring water bodies. [Display omitted] •Calcium and ferrous ions promoted inorganic P (Pi) accumulation on the periphyton.•P precipitation and coprecipitation with carbonates or Fe(OH)3 were main mechanisms.•Efficiency of Fe(II) was higher than Ca(II) in enhancing Pi abiotic accumulation.•Periphyton would help reduce P fixation in soil and P loss from the paddy fields.