Quantifying citrate-enhanced phosphate root uptake using microdialysis

AIMS: Organic acid exudation by plant roots is thought to promote phosphate (P) solubilisation and bioavailability in soils with poorly available nutrients. Here we describe a new combined experimental (microdialysis) and modelling approach to quantify citrate-enhanced P desorption and its importance for root P uptake. METHODS: To mimic the rhizosphere, microdialysis probes were placed in soil and perfused with citrate solutions (0.1, 1.0 and 10 mM) and the amount of P recovered from soil used to quantify rhizosphere P availability. Parameters in a mathematical model describing probe P uptake, citrate exudation, P movement and citrate-enhanced desorption were fit to the experimental data. These parameters were used in a model of a root which exuded citrate and absorbed P. The importance of soil citrate-P mobilisation for root P uptake was then quantified using this model. RESULTS: A plant needs to exude citrate at a rate of 0.73 μmol cm(−1) of root h(−1) to see a significant increase in P absorption. Microdialysis probes with citrate in the perfusate were shown to absorb similar quantities of P to an exuding root. CONCLUSION: A single root exuding citrate at a typical rate (4.3 × 10(−5) μmol m(−1) of root h(−1)) did not contribute significantly to P uptake. Microdialysis probes show promise for measuring rhizosphere processes when calibration experiments and mathematical modelling are used to decouple microdialysis and rhizosphere mechanisms. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s11104-019-04376-4) contains supplementary material, which is available to authorized users.