Data_Sheet_1_A Simple Approach to Isolate Slow and Fast Cycling Organic Carbon Fractions in Central European Soils—Importance of Dispersion Method.PDF

Numerous approaches have been developed to isolate fast and slow cycling soil organic carbon (SOC) pools using physical and chemical fractionation. Most of these methods are complex, expensive, and time consuming and unsuited for high-throughput application, such as for regional scale assessments. For simpler and faster fractionation via particle size the key issue is the dispersion of soil. It is unclear how the initial dispersion of soil affects the turnover rates of isolated fractions. We investigated five commonly used dispersion methods using different intensities: shaking in water, shaking in water with glass beads, ultrasonication at 100 and 450 J ml−1 and sodium hexametaphosphate (Na-HMP). We used soils from long-term field experiments that included a change from C3 to C4 vegetation and adjacent control sites using δ13C isotope ratio mass spectrometry. We evaluated the degree of C3/C4 moieties of the fractions, mass and carbon recovery and reproducibility as well as the time expenditures of the dispersions, sieving and drying techniques to develop an efficient and cheap fractionation method. Our results indicate that ultrasonication as well as H2O treatment with and without glass beads resulted in fractions with different turnover. Moreover, isolation performances depended on soil texture. While the isolation of the fractions using water with and without glass beads was equivalent to ultrasonication in soils with low clay contents, these methods had limited potential for soils with high clay contents. Furthermore, treatment with water alone had less reproducible results than other tested methods. The SOC recovery was comparable and satisfactory amongst non-chemical dispersion methods and reached over 95% for each of these methods. The use of Na-HMP was unsuccessful due to high time expenditures and strong SOC leaching. We propose particle size fractionation combined with ultrasonic dispersion as a fast and highly reliable method to quantify slow and fast cycling SOC pools for a wide range of soil types and textures from agricultural sites in central Europe.

众多方法已被开发，旨在通过物理和化学分馏技术分离快速循环与缓慢循环土壤有机碳（SOC）库。其中大部分方法复杂、昂贵且耗时，不适用于高通量应用，如区域尺度评估。通过粒径分馏实现简单快速的分离，关键问题在于土壤的分散性。土壤初始分散程度如何影响分离分馏的周转率尚不明确。本研究调查了五种常用的分散方法及其不同强度：水中摇动、含玻璃珠的水中摇动、100和450 J ml−1的超声波处理以及六偏磷酸钠（Na-HMP）。我们使用了长期田间试验中的土壤样本，包括从C3植被向C4植被的转变及相邻对照站点，并利用δ13C同位素比质谱法进行分析。我们评估了分离分馏的C3/C4组分比例、质量与碳回收率及重现性，以及分散、筛分和干燥技术的耗时，以开发一种高效且经济的分馏方法。我们的结果表明，超声波处理以及含玻璃珠或不含玻璃珠的水处理均导致具有不同周转率的分馏。此外，分离性能依赖于土壤质地。在低粘土含量的土壤中，含玻璃珠或不含玻璃珠的水处理与超声波处理在分离分馏方面效果相当，但这些方法在高粘土含量土壤中的应用潜力有限。此外，单独使用水处理的结果比其他测试方法的重现性较差。非化学分散方法中的SOC回收率相当满意，且每种方法的回收率均超过95%。由于耗时过长和强烈的SOC淋溶，使用Na-HMP未获成功。我们提议将粒径分馏与超声波分散相结合，作为一种快速且高度可靠的方法，以量化各种土壤类型和质地（来自中欧农业用地）中的缓慢和快速循环SOC库。