Importance of mechanisms and processes of the stabilisation of soil organic matter for modelling carbon turnover

Abstract

This paper reviews current knowledge of soil organic carbon (SOC) dynamics with respect to physical protection, soil moisture and temperature, and recalcitrant carbon fractions (such as charcoal) in predominantly agricultural soils. These factors are discussed within the framework of current soil organic matter models. The importance of soil structure in the stabilisation of organic residues through physical protection has been documented previously in various studies. In addition, changes in soil structure associated with tillage can significantly affect soil organic matter decomposition rates. The concept of physical protection has been incorporated into several soil carbon models as a function of soil texture. While soil texture can affect the soil's capacity for aggregation and adsorption, factors such as soil moisture and temperature may further enhance or reduce the extent of physical protection. While adsorption and aggregation can slow decomposition processes, it is unlikely that these processes are solely responsible for the high mean residence times measured in biologically active surface soils. Accordingly, chemical recalcitrance appears to be the only mechanism by which soil organic carbon can be protected for long periods of time.

Free atmospheric CO<sub>2</sub> enrichment increased above ground biomass but did not affect symbiotic N<sub>2</sub>-fixation and soil carbon dynamics in a mixed deciduous stand in Wales

“…The stability of SOM is controlled by the chemical structure of the organic matter and the existence of protection offered by the soil matrix and minerals (Baldock and Skjemstad, 2000;Krull et al, 2003;Davidson and Janssens, 2006). Oades (1993) suggested a model of aggregate formation in which micro-aggregates (∼100 µm in diameter) are formed within macro-aggregates (> 250 µm in diameter).…”

“…Finzi et al (2007) pointed out that some combination of increased N uptake from the soil and more efficient use of the N already assimilated by trees is necessary to sustain the high rates of forest NPP under elevated [CO 2 ]. Based on a larger FACE data set including a wider variety of plants, Leakey et al (2009) . From this we infer that at Bangor the major mechanism to sustain increased NPP under elevated [CO 2 ] is also based on increased NUE.…”

Storage and Turnover of Organic Matter in Soil

“…A great deal of thought has gone into defining and comparing the dominant mechanisms that affect C stability, and organizing them into a limited number of broad categories (Sollins et al 1996;Baldock and Skjemstad 2000;Krull et al 2003;Lützow et al 2006). Additionally, researchers have sought to identify the dominant mechanisms of long-term stabilization, leading some to focus on the inherent molecular recalcitrance of organic molecules (Krull et al 2003), and others on mineral interaction and protection as the fundamental controls (Van Veen and Kuikman 1990; Lützow et al 2006). Here we describe several categories of stabilization mechanisms, largely adapted from Sollins et al (1996), and place them within the context of climate, ecology, and management.…”

Storage and stability of organic matter and fossil carbon in a Luvisol and Phaeozem with continuous maize cropping: A synthesis

“…Not all constituents of soil organic matter (SOM) are rapidly converted to CO 2 , and they may be then stabilized in soil for a limited period of time. Several mechanisms have been described that contribute to SOM stabilization: (1) selective preservation resulting from recalcitrance of SOM, (2) spatial inaccessibility of soil OM to decomposer organisms due to occlusion, intercalation, hydrophobicity, and encapsulation, and (3) interaction with mineral surfaces and metal ions (e.g., Christensen, 1996;Sollins et al, 1996;Krull et al, 2003;von Lützow et al, 2006). The contribution of these different mechanisms to OM preservation in different soils and soil horizons is not well understood.…”