**4. Soil carbon preservation**

Initially, soil scientists attributed soil carbon preservation to the decomposition of particulate soil organic matter to humus, with the ever-increasing abundance of recalcitrant soil organic materials. Emerging soil concepts now strongly include studies indicating that particulate organic matter inclusion in soil structures and organic material adsorption on phyllosilicates and oxyhydroxides are major factors supporting soil organic matter preservation [23–29]. Currently debate is concentrating on the soil's formation of macro-aggregates and micro-aggregates and how these soil structures influence how soil carbon species are preserved and their residence time [23–29]. Schmidt et al. [26] reiterated that multiple influences determine soil organic matter accumulation and persistence, including: (i) root type and root biomass, (ii) physical separation of particulate organic matter from microbial activity, (iii) deep soil carbon is associated with very long turnover rates, (iv) permafrost thawing and the emission of greenhouse gases, and (v) microbial metabolic activities and community structures. Thus, all soil processes that support soil structure development and maintenance are likely to support soil carbon sequestration.
