High-resolution chemical imaging of labile phosphorus in the rhizosphere of Brassica napus L. cultivars

Phosphorus is a major limiting factor in plant growth and crop production. Phosphorus solubilisation, uptake by plant roots and efflux lead to complex, dynamic cycling of P in the vicinity of plant roots. However, direct observation of P dynamics in the rhizosphere at relevant spatial scales (sub-mm) is still lacking. Chemical imaging of the dissolved P concentration around Brassica napus roots was accomplished using diffusive gradients in thin films (DGT) coupled with laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Mathematical simulations served for investigating the capabilities of the chemical imaging technique. We show here, for the first time, localised P release along root axes and at root apices. Our results point at differential P uptake efficiencies of the two investigated B. napus cultivars. This study advances the current understanding of P dynamics in the rhizosphere and thus of plant P nutrition. This technique can serve to unravel the genotypic effects on rhizosphere mobilisation of P and hence assist breeding of highly P efficient crop cultivars.