Data Sheet 1_Competitive adsorption between phosphate and dissolved organic carbon in iron-rich soils.pdf

The competitive adsorption between phosphate and dissolved organic carbon (DOC) has been reported in Andosols and Podzols. However, the published results on the competitive adsorption between P and DOC are unclear and sometimes contradictory. The competitive behaviour between phosphate and DOC may be quite different in the surface and subsurface soils. In this study, we used surface and subsurface soils with substantial Fe oxide contents from Wagga Wagga (Chromosol) and Tumbarumba (Ferrosol) in New South Wales (Australia) to evaluate the adsorption behaviour of phosphate and DOC. Adsorption data were fitted into linear initial mass (IM) isotherm. The results showed that both surface and subsurface soils from Tumbarumba had a greater phosphate adsorption capacity than the soils from Wagga Wagga. Phosphate adsorption was greater for the subsurface soil (m = 0.72) than the surface soil (m = 0.82) from Tumbarumba, while this trend for was opposite for Wagga Wagga soils, where phosphate adsorption capacity was greater for the surface (m = 0.55) soil than the subsurface (m = 0.37) soil. The DOC adsorption was greater in the subsurface soils than the surface soils from both sites. In the mixed solution of P and DOC, phosphate adsorption promoted DOC desorption in the surface and subsurface soils from Wagga Wagga and Tumbarumba. The results of this study have crucial implications on the sustainability of Fe-rich soils. The adsorption of phosphate promoted DOC desorption in these soils, which may lead to the destabilisation of OC and impair OC sequestration and therefore enhance the microbial decomposition of OC in these soils.

磷酸盐与溶解性有机碳（Dissolved Organic Carbon, DOC）之间的竞争吸附现象已在暗色土（Andosols）和灰化土（Podzols）中被报道。然而，目前已发表的关于磷与DOC之间竞争吸附的研究结果尚不明确，且时常存在矛盾。磷酸盐与DOC的竞争吸附行为在表层土壤与下层土壤中可能存在显著差异。本研究选取澳大利亚新南威尔士州沃加沃加（Wagga Wagga，Chromosol）与滕巴伦巴（Tumbarumba，Ferrosol）两地的表层及下层土壤（均富含氧化铁（iron oxide, Fe oxide）），以探究磷酸盐与DOC的吸附行为。吸附数据通过线性初始质量（initial mass, IM）等温线模型进行拟合。结果表明，滕巴伦巴的表层与下层土壤的磷酸盐吸附容量均高于沃加沃加的对应土壤。滕巴伦巴的下层土壤（m=0.72）的磷酸盐吸附量高于其表层土壤（m=0.82）；而沃加沃加的土壤则呈现相反趋势：其表层土壤（m=0.55）的磷酸盐吸附容量高于下层土壤（m=0.37）。两地的下层土壤的DOC吸附量均高于其表层土壤。在磷与DOC的混合溶液体系中，磷酸盐的吸附作用会促进沃加沃加与滕巴伦巴两地表层及下层土壤中DOC的解吸。本研究结果对富氧化铁土壤的可持续性具有重要指导意义。磷酸盐的吸附会促进这些土壤中DOC的解吸，这可能导致有机碳（organic carbon, OC）的稳定性下降，削弱有机碳的固存能力，进而增强这些土壤中有机碳的微生物分解作用。