The effect of sample treatments on the oxygen isotopic composition of phosphate pools in soils
The effect of sample treatments on the oxygen isotopic composition of phosphate pools in soils
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DOI：
10.1016/j.chemgeo.2017.10.017
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发表时间：
2017-12-10
期刊：
影响因子：
3.9
通讯作者：
Chen, Zhi-Gang
中科院分区：
文献类型：
--
作者：
Jiang, Zhao-Hua;Zhang, Han;Chen, Zhi-Gang
磷酸盐的氧同位素组成（δ O-18（P））已越来越多地被用作土壤和其他环境中磷（P）生态地球化学循环的有效示踪剂。然而，土壤样品的预处理方法多种多样（如储存、制备和提取）。为了方法的一致性以及结果的比较，重要的是要了解特定的处理方法是否会损害原始Δ O-18（P）值。在此，使用Ag 3 PO 4和KH 2 PO 4来测试改良的赫德利连续提取和纯化程序是否可以改变磷酸盐标准品的Δ O-18（P）值。此外，为了检验样品储存和干燥条件的影响，采用消毒、储存、干燥和筛分等8种不同的预处理方法对2种土壤进行处理，然后测定各土壤P库的δ O-18（P）值。结果表明，提取纯化工艺、干燥温度（< 0 ℃至80 ℃）和筛网（20 ~ 100）对无机磷（Pi）库的δ O-18（P）值没有显著影响，但室温（不添加微生物生长促进剂-HgCl 2）储存可导致几乎所有磷库的δ O-18（P）值发生显著变化。两种土壤的δ O-18（P）从H_2O（H_2 O-Pi）→ NaHCO_3（NaHCO_3-Pi）→ NaOH（NaOH-Pi）→ HCl（HCl-Pi）依次降低，HCl浸提液中也有有机P。此外，从同位素质量平衡计算的δ O-18（P）值与测量值不同，表明在单一和连续提取方法中不同的P库的提取。总的来说，这些结果突出了需要一个统一的和标准的土壤样品的处理和提取方法，使有意义的相互比较的结果。
The oxygen isotopic composition of phosphate (delta O-18(P)) has been increasingly used as an effective tracer for the biogeochemical cycling of phosphorus (P) in soils and other environments. However, diverse pretreatment methods (e.g. storage, preparation and extraction) are being used for soil samples. For the uniformity of methods as well as for the comparison of results, it is important to understand if specific treatment methods can compromise original delta O-18(P) values. Here, Ag3PO4 and KH2PO4 were used to test whether a modified Hedley sequential extraction and purification procedure can alter the delta O-18(P) values of phosphate standards. Additionally, to test the effect of sample storage and drying conditions, two types of soils were first processed by using eight different pretreatment methods including sterilizing, storing, drying, and sieving and then the delta O-18(P) values of each soil P pool were measured. Results indicate that the extraction and purification procedure, drying temperature (< 0 degrees C to 80 degrees C) and sieving mesh (20 to 100) had no significant effect on the delta O-18(P) values of Pi (inorganic P) pools, but storage at room temperature (without microbial growth inhibitor-HgCl2 added) can lead to significant changes in delta O-18(P) values of almost all P pools. For the two soils studied, the delta O-18(P) decrease from H2O (H2O-Pi) to NaHCO3 (NaHCO3-Pi), NaOH (NaOH-Pi) and HCl (HCl-Pi), and organic P was also found in the extraction solution of HCl. Furthermore, the delta O-18(P) values calculated from isotope mass balance were different from the measured values suggesting variable extraction of different P pools during single and sequential extraction methods. Collectively these results highlight the need for a unified and standard processing and extraction methods for soil samples to allow meaningful intercomparison of results.