Millennium timescale carbon stability in an Andisol: How persistent are organo-metal complexes?
Millennium timescale carbon stability in an Andisol: How persistent are organo-metal complexes?
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DOI：
10.1016/j.geoderma.2022.115820
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发表时间：
2022
期刊：
影响因子：
6.1
通讯作者：
Hiroaki Shimada;Rota Wagai;Y. Inoue;K. Tamura;Maki Asano
中科院分区：
文献类型：
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作者：
Hiroaki Shimada;Rota Wagai;Y. Inoue;K. Tamura;Maki Asano
有机碳（OC）与活性铝和铁（金属）之间存在显著的线性相关性，这一现象在酸性土壤中经常被发现，并被解释为形成了稳定的有机金属复合物。然而，这些复合物的化学变化和长期稳定性仍不清楚。因此，我们比较了两个埋藏的A层位（埋藏期为0.5和4.6 kyr，火山灰年代学的基础上），以检查OC化学的变化，以及其与金属相提取的焦磷酸钠（PP）和酸性草酸盐（OX）。这两个视野被细分为6层，然后在每个视野中具有最高的OC层进行粒度分馏后，最大分散。14 C年龄的散装和粒度组分是一致的火山灰埋藏年龄。两个层位的有机无机组分的~（14）C年龄均较年轻，与我们以前用表面Andisol研究的结果雅阁。PP-可提取的金属浓度（金属PP）表现出非常显着的线性相关性与OC在所有的层和馏分从两个视野，而OX-可提取的金属显示的相关性只在年轻的埋层。固体13 C NMR谱表明，金属PP与烷基碳的相关性强于与芳香碳的相关性，特别是在较老的层位中，而该层位中各粒级的14 C年龄变化与芳香度无关。O-烷基C的比例显着下降，同时增加的芳香族C从年轻到老的地平线可能表明优先降解的O-烷基C的埋藏条件下。随着埋藏时间的延长，金属PP与芳香碳的相关性减弱，而金属PP与烷基碳的相关性增强。这些结果意味着在有机金属配合物中占主导地位的有机配体的移动。此外，总OC和金属PP的分布从0.2-2 μm级分到<0.2 μm级分的变化表明，有机金属络合物可能充当胶的微聚集体的物理弱化。所观察到的变化意味着降低OC稳定性，这可能会导致最终消失的埋藏A层位。目前的研究表明，虽然有机金属络合物出现持久性的OC-金属PP相关性的基础上，OC-金属协会的性质，包括部分分解的微团聚体发生的变化，在千年的时间尺度。
Significant linear correlation between organic carbon (OC) and reactive aluminum and iron (metal) are often observed across a wide range of acidic soils including Andisols, and often explained by the formation of stable organo-metal complexes. However, the chemical variation and the long-term stability of the complexes remain unclear. We thus compared two buried A horizons (the burial period of 0.5 and 4.6 kyr, based on tephra chronology) to examine the changes in OC chemistry as well as its association with the metal phases extractable by sodium pyrophosphate (PP) and acid oxalate (OX). Both horizons were subdivided into six layers, and then the layer with the highest OC in each horizon was subjected to particle-size fractionation after maximum dispersion.14C ages of the bulk and the size fractions were consistent with the tephra-based burial ages. Younger14C age was shown for the organo-mineral fractions of finer sizes in both horizons, in accord with our previous study using a surface Andisol. PP-extractable metal concentration (metalPP) showed a highly significant linear correlation with OC across all the layers and the fractions from both horizons, whereas OX-extractable metal showed the correlation only within the younger buried horizon. Solid-state13C NMR spectroscopy showed a stronger metalPPcorrelation with alkyl C than with aromatic C especially among the older horizon layers and the14C age variation among the size fractions in this horizon was not related to aromaticity. Significant decline in the proportion of O-alkyl C and concurrent increase in that of aromatic C from the younger to older horizon may suggest preferential degradation of O-alkyl C under the buried condition. Over the burial time, however, the correlation between metalPPand aromatic C weakened whereas metalPP-alkyl C correlation increased. These results imply a shift in the dominant organic ligand in the organo-metal complexes. Furthermore, the shift in the distribution of total OC and metalPPfrom 0.2–2 μm fraction to <0.2 μm fraction suggested a physical weakening of microaggregates where organo-metal complexes likely acted as glue. The observed changes imply reduced OC stability, which may lead to the eventual disappearance of buried A horizons. The current study demonstrated that, while organo-metal complexes appeared persistent based on the OC-metalPPcorrelation, the changes in the nature of OC-metal association including the partial breakdown of microaggregates took place, in the millennium timescale.