Tracing uptake and translocation of phosphorus in wheat using oxygen isotopes and mathematical modelling

Summary Understanding P uptake in soil–plant systems requires suitable P tracers. The stable oxygen isotope ratio in phosphate (expressed as δ 18 O P ) is an alternative to radioactive labelling, but the degree to which plants preserve the δ 18 O P value of the P source is unclear. We hypothesised that the source signal will be preserved in roots rather than shoots. In soil and hydroponic experiments with spring wheat ( Triticum aestivum ), we replaced irrigation water by 18 O‐labelled water for up to 10 d. We extracted plant inorganic phosphates with trichloroacetic acid (TCA), assessed temporal dynamics of δ 18 O TCA‐P values after changing to 18 O‐labelled water and combined the results with a mathematical model. Within 1 wk, full equilibration of δ 18 O TCA‐P values with the isotope value of the water in the growth medium occurred in shoots but not in roots. Model results further indicated that root δ 18 O TCA‐P values were affected by back transport of phosphate from shoots to roots, with a greater contribution of source P at higher temperatures when back transport was reduced. Root δ 18 O TCA‐P partially preserved the source signal, providing an indicator of P uptake sources. This now needs to be tested extensively for different species, soil and climate conditions to enable application in future ecosystem studies.