Nanometer scale structure of alkali-soluble bio-macromolecules of maize plant residues explains their recalcitrance in soil

The quantity and the quality of plant litter returned to the soil play an important role in the soil organic matter balance. Besides other pedo-climatic aspects, the recalcitrant molecules content of plant residue and theirs chemical composition play a main role in determining plant residue preservation. In this study we report that intrinsically resistant alkali-soluble bio-macromolecules extracted from maize plant (plant-humic acid) (plant-HA) contribute directly to the soil organic matter by just addition and conservation in the soil, and that a high syringyl/guaiacyl (S/G) ratio in the lignin residues composing plant tissue, modifying the microscopic structure of the plant alkali-soluble biopolymers enhances theirs recalcitrance because of lower accessibility of molecules to degrading enzymes. These results suggested in agreement with more recent literature that humic substance of soil consist of mixture of identifiable biopolymers coming directly from plant tissue that are added annually by maize plan residue.