Bravin M N, Tentscher P, Rose J, Hinsinger P
INRA, UMR 1222 Biogéochimie du Sol et de la Rhizosphère (INRA-SupAgro), Place Viala, 34060 Montpellier, France.
Environ Sci Technol. 2009 Aug 1;43(15):5686-91. doi: 10.1021/es900055k.
Using a root mat approach, we quantified how root-induced alkalization controlled the establishment of copper (Cu) gradients in the rhizosphere of durum wheat (Triticum turgidum durum L.) cropped in a strongly acidic, Cu-contaminated soil. Rhizosphere pH increased over 6 mm in soil, reaching up to +2.8 units close to root mat surface. Conversely, free Cu2+ activity decreased by 3 orders of magnitude and total Cu concentration by 3-fold in the rhizosphere solution, while labile Cu assessed by DGT (diffusive gradients in thin films) was halved. The DIFS (DGT-induced flux in soils and sediments) model failed to adequately simulate Cu depletion in the rhizosphere solution, showing that root-induced alkalization almost entirely explained Cu depletion while plant uptake had little impact. We modeled the observed pH gradient to recalculate its radial extension around a single root. The gradient of free Cu2+ activity in solution, deduced from pH modeling, extended over 1-4 mm in the rhizosphere depending on root radius and OH- efflux from root. Rhizosphere alkalization dramatically decreased root exposure to Cu, substantiating that root-induced chemical changes in the rhizosphere should be better accounted for to assess metal bioavailability to plants.
采用根垫法，我们量化了根系诱导的碱化作用如何控制种植在强酸性、铜污染土壤中的硬粒小麦（Triticum turgidum durum L.）根际铜（Cu）梯度的建立。根际土壤pH值在6毫米范围内升高，在根垫表面附近高达+2.8个单位。相反，根际溶液中游离Cu2+活性降低了3个数量级，总铜浓度降低了3倍，而通过DGT（薄膜扩散梯度）评估的活性铜减半。DIFS（土壤和沉积物中DGT诱导通量）模型未能充分模拟根际溶液中铜的消耗，表明根系诱导的碱化几乎完全解释了铜的消耗，而植物吸收的影响很小。我们对观察到的pH梯度进行建模，以重新计算其围绕单根的径向延伸。根据pH模型推导，溶液中游离Cu2+活性梯度在根际延伸1-4毫米，这取决于根半径和根系OH-外流。根际碱化显著降低了根系对铜的暴露，证实了在评估植物对金属的生物有效性时，应更好地考虑根际中根系诱导的化学变化。
