Organo‐mineral associations in temperate soils: Integrating biology, mineralogy, and organic matter chemistry

Abstract

We summarize progress with respect to (1) different approaches to isolate, extract, and quantify organo‐mineral compounds from soils, (2) types of mineral surfaces and associated interactions, (3) the distribution and function of soil biota at organo‐mineral surfaces, (4) the distribution and content of organo‐mineral associations, and (5) the factors controlling the turnover of organic matter (OM) in organo‐mineral associations from temperate soils. Physical fractionation achieves a rough separation between plant residues and mineral‐associated OM, which makes density or particle‐size fractionation a useful pretreatment for further differentiation of functional fractions. A part of the OM in organo‐mineral associations resists different chemical treatments, but the data obtained cannot readily be compared among each other, and more research is necessary on the processes underlying resistance to treatments for certain OM components. Studies using physical‐fractionation procedures followed by soil‐microbiological analyses revealed that organo‐mineral associations spatially isolate C sources from soil biota, making quantity and quality of OM in microhabitats an important factor controlling community composition. The distribution and activity of soil microorganisms at organo‐mineral surfaces can additionally be modified by faunal activities. Composition of OM in organo‐mineral associations is highly variable, with loamy soils having generally a higher contribution of polysaccharides, whereas mineral‐associated OM in sandy soils is often more aliphatic. Though highly reactive towards Fe oxide surfaces, lignin and phenolic components are usually depleted in organo‐mineral associations. Charred OM associated with the mineral surface contributes to a higher aromaticity in heavy fractions. The relative proportion of OC bound in organo‐mineral fractions increases with soil depth. Likewise does the strength of the bonding. Organic molecules sorbed to the mineral surfaces or precipitated by Al are effectively stabilized, indicated by reduced susceptibility towards oxidative attack, higher thermal stability, and lower bioavailability. At higher surface loading, organic C is much better bioavailable, also indicated by little 14C age. In the subsurface horizons of the soils investigated in this study, Fe oxides seem to be the most important sorbents, whereas phyllosilicate surfaces may be comparatively more important in topsoils. Specific surface area of soil minerals is not always a good predictor for C‐stabilization potentials because surface coverage is discontinuous. Recalcitrance and accessibility/aggregation seem to determine the turnover dynamics in fast and intermediate cycling OM pools, but for long‐term OC preservation the interactions with mineral surfaces, and especially with Fe oxide surfaces, are a major control in all soils investigated here.

Review on iron availability in soil: interaction of Fe minerals, plants, and microbes

“…With respect to these low-molecular-weight humic fractions, it has been clearly demonstrated that they can act efficiently as natural substrates for Fe acquisition by roots of monocots and dicots (Pinton et al 1997b(Pinton et al , 1999Cesco et al 2002). HS increase Fe bioavailability through their Fechelating properties and have redox-reactive properties (Kögel-Knabner et al 2008). These properties are related to phenolic groups contributing to Fe III reduction.…”

Biomolecule-induced carbonate genesis in abiotic formation of humic substances in nature

“…While the importance of land use and management systems on soil organic carbon pools has received considerable attention (Davidson and Janssens 2006;Ko¨gel-Knabner et al 2008), the role of the soil inorganic carbon pool in global climate change is not well understood (Lal and Kimble 2000). The present findings provide the first time evidence demonstrating that the nature and relative abundance of biomolecules, such as sugars, amino acids and polyphenols, not only have a significant effect on the generation of humic substances, but also on the formation of carbonate, both of which are mechanisms of C sequestration in the environment.…”

“…In the environment, the transformation of biomolecules originating from organized structures typical of organisms to randomly polymerized, heterogeneous humic substances characteristic of biogeochem-ical systems is pivotal to humic substance formation and subsequent organic C stabilization (Torn et al 1997;Ko¨gel-Knabner et al 2008). Abundant research evidence at the molecular level shows that mineral colloids, such as metal oxides, layer silicates and natural soil clays, can accelerate abiotic oxidative polymerization and/or polycondensation of biomolecules such as amino acids, sugars, and polyphenols derived from the breakdown of biological residues and from biological metabolites Huang 1982, 1984b;Stevenson 1994;Huang 2000;Clapp et al 2005).…”

Mechanisms of organic matter stabilization and destabilization in soils and sediments: conference introduction

“…This time around, three oral presentations (Georg Guggenberger, Ingrid Kögel-Knabner, Klaus Kaiser) directly addressed different aspects of mineral stabilization of organic matter in soils. Much of the material presented was based on a series of recent publications by this group Kögel-Knabner et al 2008). Furthermore, Johann Six presented evidence that soils have a maximum capacity for C storage which is related to ''saturation'' of mineral association (see: Six et al 2002;Chung et al 2008;Gulde et al 2008;Stewart et al 2008).…”