Comment on: neutron imaging reveals internal plant water dynamics

In a recent paper, Warren et al. (2013) illustrated the potential of neutron radiography to visualize water dynamics in soil and plants. After injection of deuterated water (D2O) in soil, the authors could monitor the changes of D2O concentration in roots. Based on the radiographs, the authors concluded that D2O was transported from roots growing in a wet soil region to roots in a dry region, proving hydraulic redistribution between roots. However, this interpretation depends on the correct estimation of D2O concentration in soil. The experiments of Warren et al. (2013) could also be explained by diffusion of D2O from soil to roots, without hydraulic redistribution within the root system.