Stability of organic matter in forest soils of the middle Central Atlas: Extraction by biochemical fractionation

Organic matter in the soil component best reflects the interactions between the soil, the biosphere, and the atmosphere, because it depends both on the nature of the soil and the bioclimatic environment, which makes it an excellent indicator of the environment (Volkoff et al., 1988). Soil organic matter consists of molecules of different sizes which are more or less associated with each other and produced by the chemical transformation of bio-based substances (miscellaneous plant litter and animal) during humification (Borie, 2011). Organic matter transformations are carried out mainly by the processes of recombination (humification) and degradation (mineralization). The formation of stable products, “humus formation or humification”, consists of recombinations and polymerizations of organic molecules, more or less complex. The biochemical nature of the organic matter brought to the soil determines the humification process (Borie, 2011). Complex humification of genesis mechanisms generates humic substances (Stevenson, 1994; Berthe, 2006), including, humin, humic acids (HA), and fulvic acids (FA), involving a variety of chemical reactions and biological transformation processes. Many factors that influence them include the origin and nature of the organic matter, the microorganisms involved in the decomposition process, and the microfauna as biological factors, as well as some physical parameters like pH, temperature, humidity, and soil aeration (Tahiri et al., 2014). The evolution of humification over time is towards obtaining high molecular weights by increasing condensation. Fulvic acids (FA) are the lightest formed early process, followed by humic acids (HA). Humin is the latest step in humification and has a very high molecular weight (Robert, 2008). Moroccan forest ecosystems, like Mediterranean forests, are composed of heterogeneous species, often clear and with diverse structures. These ecosystems generally meet their own nutrient needs through mineralization and organic matter storage in the soil. Humic substances, naturally present in a diffuse way in these * Stability of organic matter in forest soils of the middle Central Atlas: Extraction by biochemical fractionation