Abstract
Humic substances isolated from soil organic matter had been used as stimulators of plant metabolism. Arabidopsis thaliana (L.) Heynh. with only five chromosomes, short cycle and size, is an important model to evaluate the physiological effects of these substances, which are qualitatively and quantitatively influenced by morphogenesis, mineralogy and chemistry of soils. The objective of this study was to evaluate the ambience effects on bioactivity of humic acids. A and B horizons of four typical soils of the North Fluminense were sampled. After isolation and purification, humic acids were applied to plants in increasing concentrations. The number and length of lateral roots and main root length were evaluated and, subsequently, the concentrations of maximum stimulation were determined by dose-response curves and regression equations. The results showed that more stable humic acids isolated from soil in less advanced stages of weathering, high activity clay and high base saturation resulted in better physiological stimulants for Arabidopsis.
Highlights
In the soil, the chemical stability of organic matter occurs with the formation of humic substances via humification
All samples of humic acids isolated from typical soils of the North Fluminense showed the capacity to stimulate root growth in Arabidopsis higher than the control (Table 2), for example, in Figure 1, humic acids isolated from
More stable humic acids isolated from soil in less advanced stages of weathering, with high-activity clays and high base saturation were the best physiological stimulants of Arabidopsis
Summary
The chemical stability of organic matter occurs with the formation of humic substances via humification. Humic acids, as an intermediate fraction between the fulvic acids, more hydrophilic and soluble, and humin, more hydrophobic and insoluble, are listed as indicators of organic matter stability in the soil (Baldotto et al, 2010). Because their conformation and structure vary with environmental conditions, e.g., ionic strength and pH, they have the properties of biomolecules from which they are derived (Sposito, 2008) in their supra molecular arrangement, which stimulate plant growth (Façanha et al, 2002)
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