Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma The role of organo-clay associations in limiting organic matter decay: Insights from the Dajiuhu peat soil, central China Shuling Chen a , Hanlie Hong a, ⁎ , Xianyu Huang a,b , Qian Fang a , Ke Yin a , Chaowen Wang c , Yiming Zhang a , Liuling Cheng a , Thomas J. Algeo b,d,e, ⁎ a School of Earth Sciences, China University of Geosciences, Wuhan 430074, China b State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China c Gemological Institute, China University of Geosciences, Wuhan 430074, China d State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China e Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA ARTICLE INFO Handling Editor: Jan Willem Van Groenigen Keywords: Soil organic matter Clay minerals Biodegradation Alkanes Fatty acids Redox conditions ABSTRACT The mineral-bound organic matter (OM) in soils is of great importance for the global carbon cycle. Long-standing debate exists regarding the mechanisms of soil organic matter (SOM) preservation and, especially, the role of organo-clay mineral associations. Investigation of such associations is rarely undertaken in peat soils. In this study, we examine organo-clay relationships in the Dajiuhu peat soil in Hubei Province, central China, based on molecular markers, which allows for understanding of rates of OM degradation and the preservation of OM associated with clay minerals. We analyzed the major and trace element chemistry, clay mineralogy, and lipid compositions of both the coarse- and clay-sized fractions of the soil. The uniformity of trace element and REE distribution patterns in the soil (except for Layer 2) suggests that the source materials were well mixed. Chemical index of alteration (CIA) values of 70–85 indicate moderate to strong weathering processes. A significant cor- relation between C org :P and TOC may indicate that redox conditions were a significant control on OM pre- servation. The clay fraction of Dajiuhu peatland soils also has played an important role in preserving OM, especially in anoxic environments. Fourier transform infrared spectrophotometry (FTIR) and X-ray diffraction (XRD) analysis show that OM is absorbed mainly on the edges of illite grains rather than in interlayer sites. The amphoteric margins of illite crystals allow them to more effectively bind organic compounds. The high R l/h ratio, high carbon preference index (CPI), and high ratio of unsaturated-to-saturated fatty acids (C 18:2 /C 18 ) in the clay- sized fraction provide further biomarker evidence that illite efficiently protects OM from biodegradation, thus enhancing the OM content of soils. 1. Introduction Soil organic matter (SOM) contains approximately three times more carbon than the atmosphere, representing one of the largest and most active reservoirs of organic carbon on the global scale (von Lützow et al., 2006; Rumpel and Kögel-Knabner, 2011; Feng et al., 2014; Barré et al., 2017; Steffens et al., 2011). Peat soil, a unique type of soil, contains about one-third of the organic carbon in the pedosphere, even though peatland covers only 2–3% of total land area (Gorham, 1991). More than 90% of a soil's carbon inventory exists in close association with Fe-(hydr)oxide and/or minerals, especially clay minerals, which can protect organic matter (OM) from degradation in redox-active en- vironments (Kaiser and Guggenberger, 2003; Mayer, 1994; Mikutta et al., 2009; Schrumpf et al., 2013; Zeng et al., 2016). Such associations can significantly reduce the bioavailability of OM and slow down its remineralization rate (Conant et al., 2011), decreasing the amount of CO 2 emitted from soils to the atmosphere. Organic carbon stabilized by minerals has longer turnover times than particulate organic matter or organic carbon in aggregates (Trumbore, 2000). Thus, OM associated with minerals controls the long-term sedimentary sequestration of carbon and plays an important role in the global carbon cycle (Kalbitz et al., 2000; Matus et al., 2014; von Lützow et al., 2006). Mechanisms of organic carbon stabilization by minerals have been extensively investigated but still remain controversial. A number of studies have demonstrated the significance of OM-mineral interactions in a wide range of environments, such as sedimentary rocks (Li et al., 2016; Löhr et al., 2015; Playter et al., 2017), marine and coastal sedi- ments (Bianchi et al., 2016; Loehr and Kennedy, 2014), and soils https://doi.org/10.1016/j.geoderma.2018.01.013 Received 22 November 2017; Received in revised form 10 January 2018; Accepted 13 January 2018 ⁎ Corresponding authors at: State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China. E-mail addresses: honghl8311@aliyun.com (H. Hong), thomas.algeo@uc.edu (T.J. Algeo). Geoderma 320 (2018) 149–160 Available online 04 February 2018 0016-7061/ © 2018 Elsevier B.V. All rights reserved. T