Effectiveness of Humic Substances and Phenolic Compounds in Regulating Plant-Biological Functionality

Abstract

Significant benefit of soil organic matter (SOM) to crop productivity is scientifically well documented. The main constituents and active fractions of SOM are humic substances (HS) and phenolic compounds. Since both these two components strongly impact plant–soil relationship, it is importantly from an ecological point of view to discriminate their biological effects and relating them to their composition. In this study we compared the biological effects of HS, and the soil water soluble phenols (SWSP) on growth, antioxidant activities, carbohydrates, proteins, phenols, and vitamins of Pinus laricio callus. Each extract was assessed for the content of low molecular weight organic acids, soluble carbohydrates, fatty acids, and phenolic acids. Moreover, Fourier transform infrared (FT-IR) and surface-enhanced Raman scattering (SERS) spectroscopies were applied to study their molecular structure. The results showed that HS produced better callus growth compared to the control and SWSP. Carbohydrates decreased in presence of HS while proteins, vitamin C and E increased. In contrast, in callus treated with SWSP the amount of glucose and fructose increased as well as all the antioxidant activities. The data evidenced that HS rich in tartaric and fatty acids had beneficial effects on callus growth contrary to soil water-soluble phenols rich in aldehydes, and syringic, ferulic, and benzoic acids.

Chemical Structure and Biological Activity of Humic Substances Define Their Role as Plant Growth Promoters

“…Such processes may be mimicking the activity of root exudates, containing low molecular weight organic acids, and influence the molecular size and solubility of HS in the soil [ 53 , 54 ]. In addition, the carboxyl groups also contribute to determining HS solubility and biological reactivity [ 55 , 56 ].…”

“…As an example, in some research the induction of lateral root emergence was positively correlated with the lignin-derived aromatic component, whereas negatively correlated with cellulose derivatives [ 63 ]. Conversely, simple phenolic compounds, such as hydroxy-substituted benzoic and cinnamic acid derivatives were considered the most active components in other studies [ 56 , 64 ].…”

Molecular characteristics of humic substances from different origins and their effects on growth and metabolism of Pinus laricio callus

“…Earlier works indicated that plant growth and metabolism are enhanced by humic matter either rich in peptides, carbohydrates and organic acids, but poor in phenols [26] or in tartaric acid and fatty acids [27]. However, other studies suggest that it is not only the molecular composition that has a bearing on plant stimulation but also the conformational arrangement of the humic supramolecular assembly is essential in reaching and activating plant roots [8,10,40].…”

Engineered Nanomaterials in Soil: Their Impact on Soil Microbiome and Plant Health

“…Apart from soil microbiome, other organic matters of the soil such as humic substances (HS) have been known to play a vital role in plant growth, yield, and nutrition [ 106 ]. HS belong to naturally occurring organic substances which originate from the decomposition and transformation of plant, animal, and microbial residues [ 107 , 108 ]. The process of decay and transformation of plants and microbial remains in the soil generates a variety of highly acidic, relatively large, and colorful molecules which constitute HS.…”