Nitrogen fertilization has been shown to improve Cd uptake by plants but there is little information on the effects of N forms. This study examined the effects of N form on Cd bioavailability and phytoextraction in two soils differing in pH. Plants of halophytic species Carpobrotus rossii were grown in an acidic Sodosol [pH (CaCl₂) 4.9] and a neutral Vertosol (pH 7.2) spiked with 20 mg kg⁻¹ Cd as CdCl₂. Three N forms, KNO₃, (NH₄)₂SO₄ and (NH₂)₂CO at a rate of 24 mg N kg⁻¹ were applied at weekly intervals, together with nitrification inhibitor dicyanodiamide (DCD). Cadmium availability was measured, and Cd speciation in the rhizosphere analysed using synchrotron-based X-ray absorption spectroscopy. The uptake, translocation and accumulation of Cd in plants were also assessed. The reduced N forms (NH₄⁺ and urea), compared to NO₃⁻-N, decreased rhizosphere pH by 0.25 units in Sodosol and 0.72 units in Vertosol, but decreased Cd-phosphate (by 23%) only in the Vertosol. Moreover, the reduced N forms increased the extractable Cd concentration in the rhizosphere of the Vertosol by 92% and of the Sodosol by 14%. They increased root Cd concentration by 70% and Cd uptake per unit root length by 40% in the Vertosol, and increased the translocation of Cd from the roots to the shoots by 76% in the Sodosol. The results suggest that the supply of NH₄⁺-based N favors Cd phytoextraction in C. rossii.

中文翻译：

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铵基肥料可增强在两种pH值不同的土壤中生长的罗氏拟南芥中Cd的积累

氮肥已显示可改善植物对Cd的吸收，但关于N形态影响的信息很少。这项研究检查了氮的形态对两种pH值不同的土壤中Cd的生物利用度和植物提取的影响。盐生种罗氏Carbobrotus rossii的植物生长在酸性Sodosol [pH（CaCl ₂）4.9]和中性Vertosol（pH 7.2）中，掺入20 mg kg ^-1 Cd作为CdCl ₂。三种N形式KNO ₃，（NH ₄）₂ SO ₄和（NH ₂）₂ CO的比率为24 mg N kg ^-1每隔一周与硝化抑制剂双氰胺（DCD）一起使用。测量了镉的有效性，并使用基于同步加速器的X射线吸收光谱法分析了根际中的Cd形态。还评估了镉在植物中的吸收，转运和积累。还原氮形态（NH ₄ ⁺和尿素），相比NO ₃ ^--N，在Sodosol中将根际pH降低0.25个单位，在Vertosol中将其降低0.72个单位，但仅在Vertosol中降低Cd-磷酸盐（降低23％）。此外，还原的N形式使Vertosol和Sodosol根际中Cd的可提取Cd浓度增加了14％。在Vertosol中，它们使根部Cd浓度增加了70％，每单位根长Cd吸收量增加了40％，而在Sodosol中，Cd从根向芽的转运增加了76％。结果表明，基于NH ₄ ⁺的N的供应有利于C. rossii中Cd的植物提取。