Subsoil organo-mineral associations under contrasting climate conditions
Subsoil organo-mineral associations under contrasting climate conditions
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DOI：
10.1016/j.gca.2019.11.030
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发表时间：
2020-02-01
影响因子：
5
通讯作者：
Koegel-Knabner, Ingrid
中科院分区：
文献类型：
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作者：
Inagaki, Thiago M.;Possinger, Angela R.;Koegel-Knabner, Ingrid
气候差异会引起土壤中有机矿物组合的深刻变化。然而，这些变化的程度，无论是气候条件的直接影响，还是通过土壤矿物学变化的间接影响，仍不完全清楚。在这项研究中，我们旨在提高对气候和由此产生的土壤矿物学变化如何影响宏观和微观尺度下土（即 0.4-0.9 m）有机矿物相互作用的了解。在夏威夷科哈拉山的整个海拔梯度（大约 1800-2400 毫米降水年（-1）和 15-24 摄氏度）收集了一组底土样本。我们采用了大块土壤分析与矿物提取以及光谱和光谱显微分析相结合的方法。在大块土壤尺度上，土壤有机碳 (SOC) 与提取的 Fe 和 Al（连二亚硫酸柠檬酸碳酸氢盐 - DCB 和草酸铵 - OX）之间存在显着正相关性 (p < 0.05)，这支持了先前的研究，表明底土 Fe、Al 和 SOC 同时下降，降水量高于 2000 年至 2200 毫米年 (-1)。然而，使用 NanoSIMS 识别的微观有机矿物关联的差异使我们能够辨别 Fe 和 Al 在促进有机矿物关联中的相对作用。在较低降水范围（类似于 1800 mm 年（-1）），与较高降水水平（类似于 2300 mm 年（-1））相比，< 2 μm 的粘土部分显示出较高量的与 Fe 和 Al 共存的有机质（OM），其中 OM 大多不伴生或仅与 Al 伴生。虽然铁在较低降水地点贡献了约 40% 的微尺度有机矿物组合（通过与 OM 部分的共定位进行量化），但在较高降水情况下这一贡献仅为 5%。相比之下，在两种降雨水平下，Al 的贡献大致相同（约 30%）。因此，在减少气候条件下，与 Al 的结合对于 OM 的稳定可能比 Fe 更重要。当与 Al、Fe 或两者共定位时，基于单个像素的归一化 CN:C 比率被发现更高，特别是在高降水情况下。这一事实表明了铁和铝对于稳定更多富氮有机质的重要性，特别是在高降雨量的情况下。此外，较高降雨条件下的底土表现出更多还原形式的 Fe（通过 Fe K-edge XANES 评估）和较低比例的羧基-C（相对丰度低 5%）以及通过 CP-MAS C-13 NMR 测定的较高烷基/O-烷基比率。这种成分上的差异可能会直接影响两个位置的有机矿物关联，因为 Fe 还原的差异和羧基-C 基团的存在被认为在 OM 稳定中发挥作用。我们得出的结论是，微尺度上 Fe 和 Al 与 SOC 之间的空间关系表明，在较高降水量下，SOC 关联向以 Al 为主的转变，而这种关联无法仅通过大量测量来确定。因此，它们对于了解气候变化对 SOC 稳定的影响至关重要。 (C) 2019 Elsevier Ltd. 保留所有权利。
Climate differences can induce profound changes in organo-mineral associations in soils. However, the magnitude of these modifications, whether as a direct effect of climate conditions or an indirect effect through changes in soil mineralogy, are still not fully understood. In this study, we aimed to improve understanding of how climate and resultant changes in soil mineralogy affect subsoil (i.e., 0.4-0.9 m) organo-mineral interactions at the macro- and microscale. A set of subsoil samples were collected throughout an elevation gradient (approximately 1800-2400 mm precipitation year(-1) and 15-24 degrees C) on Kohala Mountain, Hawaii. We carried out a combined approach of bulk soil analyses with mineral extractions and spectroscopic and spectromicroscopic analyses. Significant positive correlations (p < 0.05) between soil organic carbon (SOC) with extracted Fe and Al (dithionite citrate bicarbonate - DCB and ammonium oxalate - OX) at the bulk soil scale supported prior research showing concurrent decline of subsoil Fe, Al and SOC above a precipitation level of similar to 2000 to similar to 2200 mm year(-1). However, divergence in microscale organo-mineral associations identified using NanoSIMS allowed us to discern the relative roles of Fe and Al in promoting organo-mineral associations. At the lower precipitation range (similar to 1800 mm year(-1)), the clay fraction < 2 mu m showed higher amounts of organic matter (OM) co-localized with Fe & Al compared with the higher precipitation level (similar to 2300 mm year(-1)), where OM was mostly unassociated or only associated with Al. While Fe contributed to approximately 40% of the microscale organo-mineral associations in the lower precipitation site (quantified by co-localizations with OM segments), this contribution at the higher rainfall regime was only 5%. In contrast, the contribution of Al was approximately the same in both rainfall levels (approximately 30%). Therefore, associations with Al may be more important than Fe for OM stabilization under reducing climate conditions. The normalized CN:C ratio based on individual pixels was found to be higher when co-localized with Al, Fe, or both, especially under the high precipitation regime. This fact points towards the importance of Fe and Al to stabilize more N-rich OM, especially at high rainfall levels. In addition, subsoil from higher rainfall conditions exhibited more reduced forms of Fe (assessed by Fe K-edge XANES) and lower proportions of carboxyl-C (5% lower in the relative abundance) as well as higher alkyl/O-alkyl ratios determined by CP-MAS C-13 NMR. Such differences in composition may directly influence the organo-mineral associations at both locations, as differences in Fe reduction and the presence of carboxyl-C groups are recognized to play a role in OM stabilization. We conclude that spatial relationships between Fe and Al with SOC at the microscale show a shift towards Al-dominated SOC associations at higher precipitation that could not be ascertained from bulk measurements alone. Therefore, they are of fundamental importance to understand the impact of climate change on SOC stabilization. (C) 2019 Elsevier Ltd. All rights reserved.