Humic fractions were shown to be closely involved in gene expression
and promotion of different PM H+-ATPase isoforms, as well as in lateral root
development, indicating an enhanced nutrient absorption capacity of the plant
root system. HPLC-SEC confirmed that water-soluble humic substances (WSHS)
correspond to a subfraction of the fulvic fraction of humic substances. This was
supported by E465/E665 ratios higher than 8.5. These ratios generally increased over
the growing season in cultivated soils but showed significant differences between
conventionally and organically managed bare soils. FTIR data and the analytical
quantification of carboxyls confirmed relevant structural changes in bare soil under
both organic and conventional farming management. Absorption intensities ratios
at 1,590–1,570 cm-1 and 1,440–1,380 cm-1 showed the predominant aliphatic
character of these molecules.
