Browsing by Author "Roose, Tiina"

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    A model of uranium uptake by plant roots allowing for root-induced changes in the soil
    (American Chemical Society, 2018-02-21) Boghi, Andrea; Roose, Tiina; Kirk, Guy J. D.
    We develop a model with which to study the poorly understood mechanisms of uranium (U) uptake by plants. The model is based on equations for transport and reaction of U and acids and bases in the rhizosphere around cylindrical plant roots. It allows for the speciation of U with hydroxyl, carbonate, and organic ligands in the soil solution; the nature and kinetics of sorption reactions with the soil solid; and the effects of root-induced changes in rhizosphere pH. A sensitivity analysis showed the importance of soil sorption and speciation parameters as influenced by pH and CO2 pressure; and of root geometry and root-induced acid–base changes linked to the form of nitrogen taken up by the root. The root absorbing coefficient for U, relating influx to the concentration of U species in solution at the root surface, was also important. Simplified empirical models of U uptake by different plant species and soil types need to account for these effects.
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    Soil carbon dioxide venting through rice roots
    (Wiley, 2019-08-04) Kirk, Guy J. D.; Boghi, Andrea; Affholder, Marie-Cecile; Keyes, Samuel D.; Heppell, James; Roose, Tiina
    The growth of rice in submerged soils depends on its ability to form continuous gas channels—aerenchyma—through which oxygen (O2) diffuses from the shoots to aerate the roots. Less well understood is the extent to which aerenchyma permits venting of respiratory carbon dioxide (CO2) in the opposite direction. Large, potentially toxic concentrations of dissolved CO2 develop in submerged rice soils. We show using X‐ray computed tomography and image‐based mathematical modelling that CO2 venting through rice roots is far greater than thought hitherto. We found rates of venting equivalent to a third of the daily CO2 fixation in photosynthesis. Without this venting through the roots, the concentrations of CO2 and associated bicarbonate (HCO3−) in root cells would have been well above levels known to be toxic to roots. Removal of CO2 and hence carbonic acid (H2CO3) from the soil was sufficient to increase the pH in the rhizosphere close to the roots by 0.7 units, which is sufficient to solubilize or immobilize various nutrients and toxicants. A sensitivity analysis of the model showed that such changes are expected for a wide range of plant and soil conditions.
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    Uranium diffusion and time-dependent adsorption–desorption in soil: a model and experimental testing of the model
    (Wiley, 2019-04-01) Darmovzalova, Jana; Boghi, Andrea; Otten, Wilfred; Eades, Lorna J.; Roose, Tiina; Kirk, Guy J. D.
    Most past research on uranium (U) transport and reaction in the environment has been concerned with groundwater contamination and not with uptake by plants or soil biota, both of which operate over much smaller time and distance scales. We developed and tested a model of U diffusion and reaction in soil at scales appropriate for uptake by plant roots, based on a model we developed in an earlier paper. The model allows for the speciation of U with hydroxyl, carbonate and organic ligands in the soil solution, and the nature and kinetics of sorption reactions with the soil solid. The model predictions were compared with experimentally‐measured concentration‐distance profiles of U in soil adjusted to different pHs and CO2 pressures. Excellent agreement between observed and predicted profiles was obtained using model input parameters measured or otherwise estimated independently of the concentration‐distance profiles, showing that the model was a correct description of the system and all important processes were allowed for. The importance of the kinetics of U adsorption and desorption on the time‐scale of diffusion through the soil is highlighted. The results are discussed in terms of the uptake of U by plant root systems, as modelled in the earlier paper.