Iron oxides selectively stabilize plant‐derived polysaccharides and aliphatic compounds in agricultural soils

Abstract

A strong link exists between iron oxides and soil organic carbon (SOC). However, the role of iron oxides in the preservation of SOC in agricultural soil remains poorly understood. In this study, we comprehensively examined the concentration, molecular composition and biological sources of iron oxide‐bound organic carbon (Fe‐bound OC) in arable soils collected from 12 sites in central and east China. The results indicated that 6.2–31.2% of the SOC was bound to iron oxides in agricultural soil and that the binding mechanisms varied from adsorption in most soils to coprecipitation in those with a large content of organic carbon. The distribution of Fe‐bound OC showed no clear variation in relation to site, but Fe‐bound OC reached a peak in soils with an annual mean temperature of 16.4°C. Correlation analysis demonstrated that TOC might be the main determinant for the amount of Fe‐bound OC and that the binding mechanism is influenced by both TOC and the active Fe ratio. Comprehensive studies of C/N, 13C isotope and synchrotron radiation‐based Fourier transform infrared (SR‐FTIR) spectroscopy showed that iron oxides selectively protected plant‐derived aliphatic compounds and polysaccharides in agricultural soil. This study revealed the quantitative characterization, biological sources and molecular composition of Fe‐bound OC in arable soils, which provides useful information for evaluating and managing the global C cycle under the framework of climate change.

Variation of intra‐aggregate organic carbon affects aggregate formation and stability during organic manure fertilization in a fluvo‐aquic soil

“…This was also consistent with our findings which MWD and PSA 1 were significantly and positively correlated with the abundance of fungi and negatively correlated with G+: G‐ within macroaggregates (Table 6). Moreover, the significantly positive correlations of the polysaccharide‐C of fine iPOM within macroaggregates with MWD and PSA 1 (Table 6) indicated that more polysaccharide‐C can be easily encrusted with mineral particles to facilitate macroaggregate formation and stabilization (Six et al., 2004; Wan et al., 2019).…”

Delineating the Role of Calcium in the Large‐Scale Distribution of Metal‐Bound Organic Carbon in Soils

“…Organic carbon (OC) associated with reactive metal oxides, especially noncrystalline ferric iron [Fe(III)] and aluminum (Al) (hydr)oxides, is commonly assessed by the citrate‐bicarbonate‐dithionite (CBD) method (termed “metal‐bound OC” or abbreviated as “OC CBD ” hereafter) and estimated to constitute 15%–38% of total OC in sediments and upland soils (Shields et al., 2016; Zhao et al., 2016). However, the relative importance of OC CBD in different land types (e.g., uplands vs. wetlands) and soil depths remains unclear (Mu et al., 2016; Rasmussen et al., 2018; Wan et al., 2019; Zhao et al., 2016), hampering our ability to predict and protect this important OC pool that is vital for the long‐term preservation of soil organic carbon (SOC) (Hemingway et al., 2019; Schmidt et al., 2011).…”

Organic carbon preservation promoted by aromatic compound-iron complexes through manure fertilization in red soil

“…However, the formation of MOM between non-crystalline mineral oxides and specific organic compounds is still unclear. Wan et al (2019) reported that Fe oxides were selectively associated with polysaccharides and aliphatic compounds in different types of agricultural soil. Zhao et al (2016) considered that aromatic compounds were the main component of the organo-Fe complexes.…”