Cultivated organic soils make a significant contribution to phosphorus (P) leaching losses from agricultural land, despite occupying a small proportion of cultivated area. However, less is known about P mobilisation processes and the P forms present in peat soils compared with mineral soils. In this study, P forms and their distribution with depth were investigated in two cultivated Histosol profiles, using a combination of wet chemical extraction and P K-edge X-ray absorption near-edge structure (XANES) spectroscopy.Both profiles had elevated P content in the topsoil, amounting to around 40 mmol kg(-1), and P speciation in both profiles was strongly dominated by organic P. Topsoils were particularly rich in organic P (P-org), with relative proportions of up to 80%. Inorganic P in the profiles was almost exclusively adsorbed to surface reactive aluminium (Al) and iron (Fe) minerals. In one of the pro-files, small contributions of Ca-phosphates were detected.A commonly used P saturation index (PSI) based on ammonium-oxalate extraction indicated a low to moderate risk of P leaching from both profiles. However, the capacity of soil Al and Fe to retain P in organic soils could be reduced by high competition from organic compounds for sorption sites. This is not directly accounted for in PSI and similar indices.Accumulation of P-org in the topsoil may be attributable by microbial peat decomposition and transformation of mineral fertiliser P by both microbiota and crops. Moreover, high carbon-phosphorus ratio in the surface peat material in both profiles suggests reduced net mineralisation of P-org in the two soils. However, advancing microbial peat decomposition will eventually lead to complete loss of peat horizons and to mineralisation of P-org. Hence, P-org in both profiles represents a huge potentially mobilised P pool.

中文翻译：

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P K-edge XANES光谱揭示有机土壤中的磷形态

尽管耕地有机土壤占耕地面积很小，但它对农业用地磷 (P) 浸出损失做出了重大贡献。然而，与矿质土壤相比，泥炭土壤中磷的动员过程和磷的形式知之甚少。在这项研究中，使用湿化学提取和 P K 边缘 X 射线吸收近边结构 (XANES) 光谱的组合，在两个培养的 Histosol 剖面中研究了 P 的形式及其随深度的分布。 两个剖面都提高了 P 含量在表土中，总量约为 40 mmol kg(-1)，并且两个剖面中的 P 形态均以有机 P 为主。表土中有机 P (P-org) 特别丰富，相对比例高达 80%。剖面中的无机 P 几乎完全吸附在表面活性铝 (Al) 和铁 (Fe) 矿物上。在其中一个配置文件中，检测到钙磷酸盐的小贡献。基于草酸铵提取的常用 P 饱和指数 (PSI) 表明 P 从两个配置文件中浸出的风险低至中等。然而，有机化合物对吸附位点的激烈竞争可能会降低土壤铝和铁在有机土壤中保留磷的能力。这在 PSI 和类似指数中没有直接考虑。表土中 P-org 的积累可能是由于微生物泥炭分解和微生物群和作物对矿物肥料 P 的转化。而且，两个剖面中表面泥炭材料中的高碳磷比表明两种土壤中 P-org 的净矿化减少。然而，推进微生物泥炭分解最终将导致泥炭层的完全丧失和 P-org 的矿化。因此，两个配置文件中的 P-org 都代表了一个巨大的潜在动员 P 池。