Stabilization of Organic Carbon via Chemical Interactions with Fe and Al Oxides in Gley Soils

Abstract

The importance of soil organic carbon (SOC) stabilization via chemical interactions with Fe and Al oxide minerals within gley soils remains unclear. Changes in the proportions of Fe/Al oxides and SOC and N contents associated with Fe/Al oxides within the profiles of gley soils under contrasting hydrological regimes and freely draining control soils from Harwood Forest (northeast England) were investigated. Sequential selective dissolution techniques were used to measure Fe/Al oxide crystallinity and explore whether crystallinity differed between gleyed and freely draining soils. Extracts were analyzed using Fourier transform infrared spectroscopy to investigate the chemical characteristics of organic matter (OM) associated with Fe/Al oxides. Strongly crystalline Fe oxides were the dominant (∼50%–80% of total Fe oxides present) mineral phase in gley mineral soils. Contrasting gley soil hydrological regimes influenced total subsoil Fe and total and weakly crystalline Al oxide concentrations. Also, within-profile changes in strongly crystalline Fe oxide concentrations were linked to differences in hydrological and redox conditions. A large proportion of SOC (generally 70%–90% of total) seemed to be associated with Fe/Al oxides. Correlation plots, however, indicated that SOC contents were not linearly related to amounts of total Fe and Al oxides, weakly crystalline Fe and Al oxides, or strongly crystalline Fe oxides. The lack of linear correlations observed for these acidic soils may be caused by contributions from other extractable soil components and factors such as high organic loadings and insufficient amounts of Fe/Al oxides for interaction with SOC in topsoils and variable surface loadings of different organic inputs at different soil depths. Subsoil C/N ratios (∼18–21) were higher than those in extracted subsoil residues (∼9–17), suggesting that minerals other than Fe/Al oxides preferentially adsorbed N-rich microbially processed compounds. The OM associated with weakly and strongly crystalline Fe/Al oxides was chemically different, the latter generally having greater hydroxyl, aliphatic, carboxylate, and /or phenolic character and less carbohydrate character than the former. This research shows that interactions between Fe/Al oxides and SOM in redox-dynamic gley soils under different hydrological regimes are complex, and further investigations of SOC stabilization in these systems using selective dissolution and other complementary techniques are required

Large‐Scale Distribution of Molecular Components in Chinese Grassland Soils: The Influence of Input and Decomposition Processes

“…Other than soil pH, both Al d contents and BGB have strong positive effects on the abundance of all compound groups in the alpine grassland soils ( p < 0.05; Figures and ). The former trend can be attributed to the strong sorption capacity of reactive Al oxides for soil aliphatic components (Cloy et al, ; Fleury et al, ; Mikutta et al, ; Ulrich et al, ) and carbohydrates (Cloy et al, ; Miltner & Zech, ), contributing to their enhanced preservation in the soil. By comparison, the latter trend is, to a large extent, a reflection that plant roots are a key source of solvent‐extractable compounds in the alpine grassland soils and that such input signals are not significantly altered by decomposition processes, which are inhibited by low temperatures in the alpine regions (Baumann et al, ; Liu et al, ).…”

Effect of Land Use Change on Molecular Composition and Concentration of Organic Matter in an Oxisol

“…Surface hydroxyl (−OH) groups of the crystalline Fe/Al phase can directly bind OM compounds through inner-sphere complexations via ligand exchange . This strong inner-sphere complexation contributes to the long-term OM preservation from microbial decomposition. , …”

“…67 This strong inner-sphere complexation contributes to the long-term OM preservation from microbial decomposition. 52,68 Molecular Composition of Extractable OM Fractions. The chemical characteristics of OM in the water-soluble fraction were very diverse, with H/C ranging from 0.30 to 2.23 and O/C ranging from 0.02 to 1.18 (Figure 4).…”

Controlled assembly of heterogeneous aggregates of clay, iron hydr(oxydes) and polysaccharide: Effects of preparation conditions

“…The apparent higher amount of adsorbed Dextran is related to the presence of nanoFeH on the surface of illite platelets, which leads to the following questions: what is the exact mechanism of aggregate formation and what is the exact role played by nanoFeH? The affinity of iron oxides for organic matter was reported in numerous studies (Reinhardt and Wilkinson, 2004;Cloy et al, 2014;Vindedahl et al, 2016;Sowers et al, 2018b), so that it is likely that the presence of nanoFeH enhanced Dextran adsorption. For Fe-montmorillonite heteroaggregates (Ji et al, 2004), it was suggested that the presence of FeH reduced the charge and electric field of clay particles.…”