Structural Characterization and Bioactivity of Humic and Fulvic Acids Extracted from Preserved and Degraded Brazilian Cerrado Biomes Soils

Humic substances are an important soil quality indicator, influencing its physical-chemical and biological characteristics while directly affecting plant growth, through their biostimulant activity. To elucidate the role of humic substances in seedlings acclimation it's important to establish a relationship among the origin, the structural composition and their biological activity. The aim of the present paper is to characterize the soluble humic fractions extracted from soils of the Brazilian Cerrado biome with different levels of preservation, and to verify their biological activity on seedlings of the pioneer Cerrado native species Enterolobium contortisiliquum (Vell.) Morong. Humic and fulvic acids were isolated from preserved and degraded Cerrado areas. Humic compounds were characterized assessing total acidity, UV-VIS and IR spectra. Humic substances bioactivity was evaluated on E. contortisiliquum seedlings grown in Leonard pots, supplied with nutrient solution added with the optimal concentrations of humic and fulvic acids and their mix. Seedlings root structure, antioxidant enzymes activity and photosynthetic pigments contents were evaluated. The humic substances showed different chemical characteristics and bioactivity depending on sampling area. Mixed humic and fulvic acids showed higher efficacy, especially those coming from the preserved area. It is noteworthy that A) the type of management influences humic fraction chemical structure, well reflected in their biological activity B) E. contortisiliquum, shows a better response to humic substances coming from a well-established and stable canopy.