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Published on: August 22, 2014
Quantifying citrate-enhanced phosphate root uptake using microdialysis
D M McKay Fletcher1, R Shaw2, A R Sánchez-Rodríguez2,3
1Bioengineering Sciences Research Group, Department of Mechanical Engineering, School of Engineering Sciences, Faculty of Engineering and Physical Sciences, University of Southampton, University Road, Southampton, SO17 1BJ UK.
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.
