Computed tomographic evaluation of osmotica on shrinkage and recovery of lupin (Lupinus angustifolius L.) and radish (Raphanus sativus L.) roots

X-ray computed tomography (CT) may be a useful tool to evaluate in situ root response to environmental change. The effects of increasing strength of NaCl osmotic solution on the shrinkage and recovery of radish and lupin roots were examined using X-ray computed tomography (CT). The radish and lupin roots showed different patterns of response to osmotic treatments depending on the level of osmotic potential applied. For the highest osmotic potential treatment (−0.10 MPa), radish root cross-sectional areas decreased slightly (1.4%) while the lupin root cross-sectional area increased slightly (2.6%). For the lowest osmotic potential treatments (−2.0 MPa), radish roots shrank by 72.3% as compared to 54% for lupin roots. Recovery patterns of both roots were remarkably different. While radish roots exposed to the lowest osmotic treatment were able to recover all but 14% of their original volume after removal of osmotic treatments, lupin roots were fatally injured by this extreme treatment and died. The physical density of the radish and lupin roots, as reflected by X-ray CT attenuation coefficients, differed by a factor of 18. Differences in physical density reflected changes in root water content, extent and volume of Donnan free space as well as root composition. Furthermore, increases or decreases in CT Hounsfield unit values were associated with a parallel increase or decrease in root physical density which in turn reflects the direction of water movement. Data obtained in this study illustrate the dramatic variation in response in which different plant species can tolerate salinity and the usefulness of CT as a tool to study these effects.