Wagner Stefan, Hoefer Christoph, Puschenreiter Markus, Wenzel Walter W, Oburger Eva, Hann Stephan, Robinson Brett, Kretzschmar Ruben, Santner Jakob
Department of Forest and Soil Sciences, Institute of Soil Research, Rhizosphere Ecology & Biogeochemistry Group, University of Natural Resources and Life Sciences, Vienna, Konrad-Lorenz-Strasse 24, 3430, Tulln, Austria.
Department General, Analytical and Physical Chemistry, Chair of General and Analytical Chemistry, Montanuniversität Leoben, Franz-Josef-Strasse 18, 8700, Leoben, Austria.
Environ Exp Bot. 2020 May 20;177:104122. doi: 10.1016/j.envexpbot.2020.104122. eCollection 2020 Sep.
(PV) and (PQ) are reported to hyperaccumulate arsenic (As) when grown in Asrich soil. Yet, little is known about the impact of their unique As accumulation mechanisms on As transformations and cycling at the soil-root interface. Using a combined approach of two-dimensional (2D), sub-mm scale solute imaging of arsenite (As), arsenate (As), phosphorus (P), manganese (Mn), iron (Fe) and oxygen (O), we found localized patterns of As/As redox transformations in the PV rhizosphere (As/As ratio of 0.57) compared to bulk soil (As/As ratio of ≤0.04). Our data indicate that the high As root uptake, translocation and accumulation from the As-rich experimental soil (2080 mg kg) to PV fronds (6986 mg kg) induced As detoxification via As reduction and As root efflux, leading to As accumulation and re-oxidation to As in the rhizosphere porewater. This As cycling mechanism is linked to the reduction of O2 and Mn (oxyhydr)oxides resulting in decreased O2 levels and increased Mn solubilization along roots. Compared to PV, we found 4-fold lower As translocation to PQ fronds (1611 mg kg), 2-fold lower As depletion in the PQ rhizosphere, and no As efflux from PQ roots, suggesting that PQ efficiently controls As uptake to avoid toxic As levels in roots. Analysis of root exudates obtained from soil-grown PV showed that As acquisition by PV roots was not associated with phytic acid release. Our study demonstrates that two closely-related As-accumulating ferns have distinct mechanisms for As uptake modulating As cycling in As-rich environments.
据报道，蜈蚣草（PV）和凤尾蕨（PQ）在富含砷的土壤中生长时会超积累砷（As）。然而，关于它们独特的砷积累机制对土壤 - 根际界面处砷转化和循环的影响却知之甚少。通过采用二维（2D）、亚毫米尺度的亚砷酸盐（As(III)）、砷酸盐（As(V)）、磷（P）、锰（Mn）、铁（Fe）和氧（O）溶质成像的组合方法，我们发现与 bulk soil（As(III)/As(V) 比率≤0.04）相比，蜈蚣草根际存在 As(III)/As(V) 氧化还原转化的局部模式（As(III)/As(V) 比率为 0.57）。我们的数据表明，从富含砷的实验土壤（2080 mg kg⁻¹）到蜈蚣草叶片（6986 mg kg⁻¹）的高砷根吸收、转运和积累通过砷还原和砷根外流诱导了砷解毒，导致砷在根际孔隙水中积累并重新氧化为 As(V)。这种砷循环机制与 O₂ 和 Mn（氢）氧化物的还原有关，导致根际 O₂ 水平降低和 Mn 溶解度增加。与蜈蚣草相比，我们发现凤尾蕨叶片中的砷转运降低了 4 倍（1611 mg kg⁻¹），凤尾草根际的砷消耗降低了 2 倍，并且凤尾草根没有砷外流，这表明凤尾蕨有效地控制了砷的吸收以避免根部有毒的砷水平。对从土壤种植的蜈蚣草中获得的根系分泌物的分析表明，蜈蚣草根对砷的获取与植酸释放无关。我们的研究表明，两种密切相关的砷积累蕨类植物在富砷环境中具有不同的砷吸收机制来调节砷循环。
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