Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas, Serrano 115 bis, 28006, Madrid, Spain.
Department of Agricultural, Food and Environmental Sciences, Polytechnic University of Marche, via Brecce Bianche 10, 60131, Ancona, Italy.
Sci Rep. 2019 Jul 12;9(1):10146. doi: 10.1038/s41598-019-46577-y.
Physical fractionation methods used in soil organic matter (SOM) research commonly include density-based procedures with heavy liquids to separate SOM pools with varying turnover rates and functions. Once separated, the heavy SOM pools are often thoroughly rinsed with water to wash off any residues of the heavy liquids. Using four soils with contrasting properties, we investigated the effects of using either sodium polytungstate (SPT) or sodium iodide (NaI), two of the most commonly used heavy liquids, on the distribution of organic carbon (C) and total nitrogen (N) in free light, intra-aggregate light, and mineral-associated heavy SOM pools isolated by a common fractionation scheme. We also determined the effects of washing the mineral-associated heavy SOM fractions on the recovery of organic C and total N after separation. Because of its smaller viscosity compared to that of NaI, SPT consistently yielded greater intra-aggregate and smaller mineral-associated soil organic C contents. We also confirm that some commercial SPT products, such as the one used here, can contaminate organo-mineral heavy pools with N during density-based fractionation procedures. We do not recommend the repeated washing of heavy fractions separated with Na-based heavy liquids, as this can mobilize SOM.
物理分馏方法常用于土壤有机质 (SOM) 研究，通常包括基于密度的程序和重液，以分离具有不同周转率和功能的 SOM 池。一旦分离，重 SOM 池通常会用大量的水彻底冲洗，以洗掉重液的任何残留物。我们使用四种具有不同性质的土壤，研究了使用两种最常用的重液，即多钨酸钠 (SPT) 和碘化钠 (NaI)，对通过常见分馏方案分离的游离轻组、内团聚体轻组和矿物结合重组 SOM 池中的有机碳 (C) 和总氮 (N) 分布的影响。我们还确定了洗涤矿物结合重组 SOM 馏分对分离后有机 C 和总 N 回收率的影响。由于 SPT 的粘度比 NaI 小，因此它始终产生更大的内团聚体和更小的矿物结合土壤有机 C 含量。我们还证实，某些商业 SPT 产品（如这里使用的产品）在基于密度的分馏过程中可以用 N 污染有机-矿物重池。我们不建议重复洗涤用基于 Na 的重液分离的重馏分，因为这可能会使 SOM 移动。
