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. 2005. Net Cd 2+ flux at the root surface of durum wheat (Triticum turgidum L. var. durum) cultivars in relation to cultivar differences in Cd accumulation. Can. J. Plant Sci. 85: 103-107. Net Cd 2+ flux and Cd accumulation for four durum wheat cultivars were measured to determine whether the net Cd 2+ flux to the roots plays a role in cultivar differences in Cd accumulation. Plants were germinated for 4 d in the dark and then grown hydroponically for 2 d before being placed in a Petri dish with their roots immersed in a 1.0 µM Cd solution. Net Cd 2+ flux to the root was measured at ten positions located 0.5 mm to 25 mm from the root tip. Cadmium concentrations were measured using Cd 2+ -selective microelectrodes; Cd 2+ flux to the root surface was then calculated using the MIFE™ system. The flux was greatest nearest the root tip (within 1.5 mm of the tip) and there were no significant differences in net Cd 2+ flux among the various cultivars -likely because of the absence of a Casparian strip in the root tip cells. Net Cd 2+ flux decreased with increasing distance from the root tip, with significant differences among cultivars. The mean Cd 2+ flux to the roots in the 2-25 mm region increased in the following order: Arcola ≈ G9265-AU ≈ Kyle < G9265-BF, with the low grain Cd accumulators (Arcola and G9265-AU) generally exhibiting lower fluxes than the high grain Cd accumulators (Kyle and G9265-BF). However, net Cd 2+ flux did not correspond to total plant Cd content, which increased in the order: G9265-AU < G9265-BF < Kyle < Arcola. We conclude that while there are durum wheat cultivar differences in the net Cd 2+ flux at the root surface, their contribution to cultivar differences in total plant Cd accumulation is generally overshadowed by one or more other Cd accumulation factors. À cette fin, ils ont fait germer des graines dans l'obscurité pendant quatre jours puis ont cultivé les plantules en milieu hydroponique deux jours de plus avant de les placer dans des boîtes de Pétri, racines plongées dans une solution à 1,0 µM de Cd. Ils ont établi le flux net de Cd 2+ à dix endroits situés entre 0,5 et 25 mm de l'extrémité de la racine. La concentration de cadmium a été dosée au moyen de microélec-trodes sélectives pour les ions Cd 2+ . Ensuite, les auteurs ont calculé le flux à la surface de la racine grâce au système MIFE MC . Le flux le plus important a été relevé près du bout de la racine (à moins de 1,5 mm), mais il n'existe pas de variation significative du flux net d'ions Cd 2+ entre les cultivars, sans doute parce que les cellules à l'apex n'ont pas de bande casparienne. Le flux net d'ions Cd 2+ diminue à mesure qu'on s'éloigne de l'extrémité de la racine et les cultivars montrent des écarts importants. Le flux moyen d'ions Cd 2+ dans la partie des racines située de 2 à 25 mm de l'extrémité augmente dans l'ordre suivant : Arcola ≈ G9265-AU ≈ Kyle < G9265-BF. Les cultivars qui accumulent peu de Cd dans le grain (Arcola et G9265-AU) se caractérisent par un flux plus faible que ceux au grain contenant beaucou...

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Research has suggested a link between the bioavailability of soil Cd and total soil organic matter. However, some research suggested a negative relationship between total soil organic matter and bioavailable soil Cd while other research suggested a positive relationship. This study investigated the relationship between soil Cd and both the quantity and quality of soil organic matter as influenced by long-term cultivation. Two Orthic Chernozemic surface soil samples, one from a virgin prairie and the other from an adjacent cultivated prairie, were collected from each of 12 different sites throughout southern Saskatchewan, Canada. The samples were analyzed for total organic C, total Cd, Cd availability index (CAI), and pH. The nature of the soil organic matter was investigated with 13C Cross Polarization Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy (13C CPMAS NMR). The total soil Cd, CAI, and total soil organic C of the cultivated soils were significantly lower than those of the virgin soils whereas the opposite trend was observed for the soil pH and the aromaticity of the organic C. The reduced CAI in the cultivated soils was related to the increase in both the soil pH and the aromaticity of the organic C. No relationship was found between the CAI and the soil organic C content, but a significant positive correlation was found between total organic C and total Cd in both the virgin and the cultivated soils. As well, a significant positive correlation was found between the fraction of total Cd removed from the soil after long-term cultivation and the corresponding fraction of organic C removed. Key words: Long-term cultivation, soil organic matter, 13C CPMAS NMR, cadmium

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