Chemical properties of humic matter as related to induction of plant lateral roots

Abstract

A series of humic matter samples isolated from a soil sequence, different oxisols, size‐fractionated from a vermicompost humic acid and subjected to chemical modifications, were characterized by CPMAS 13C‐NMR spectroscopy. The relative signal areas in chemical shift regions of NMR spectra of the four sets of samples were analysed by principal component analysis (PCA). Hierarchical cluster analysis (HCA) was applied to build a classification model, which allowed the recognition of humic matter according to its origin. The relationship between carbon species and biological activity of humic acids, as promoters of lateral root emergence, was obtained by applying PLS multivariate analysis. This showed that lateral root emergence was mostly related to NMR parameters such as the hydrophobicity index (HB/HI) and the 40–110 and 160–200 ppm chemical shift regions (hydrophilic carbon HI), while the content of hydrophobic (HB) carbon in humic samples was negatively correlated with induction of lateral root hair. Our results represent a step further in the structure‐bioactivity relationship of natural humic substances and confirm their role as plant root growth promoters.

Humic matter elicits proton and calcium fluxes and signaling dependent on Ca2+-dependent protein kinase (CDPK) at early stages of lateral plant root development

“…HS effects may be either stimulating or inhibiting plant activities, depending on their origin, molecular composition, and concentration, and also varying with plant species and interactions with symbiotic microorganisms [3]. Despite prolonged efforts aimed to correlate molecular composition and structural arrangements of humic substances with their biological activity on higher plants, the involved mechanisms of action are yet to be elucidated [4][5][6][7].…”

The biostimulant manufactured using diazotrophic endophytic bacteria and humates is effective to increase sugarcane yield

“…The nature of chemical composition of humic substances was revealed [12] allowing the relationship between chemical properties of humic matter and their physiological effects [13,14]. However, there is a disagreement between results accumulated in the laboratory and the field response of the biostimulants.…”

Effect of contrasting crop rotation systems on soil chemical, biochemical properties and plant root growth in organic farming: first results

“…The higher amount of humic substances in the upper layer of the P-C soil may also have favoured the major root density observed. Indeed, these molecules are widely studied and considered to be root growth promoters by acting as morphogenic compounds which are able to modulate for meristematic cell activity and the hyperinduction of sites of lateral root emergence (Canellas et al, 2012).…”

“…In addition to crop production, the level of available nutrients can influence post-embryonic root development and root architecture (López-Bucio et al, 2003). Finally, humic substances can directly induce the proliferation of lateral roots and root hairs or indirectly mediate for the up-take of nutrients (Canellas et al, 2012). The main aim of this study is to test the hypotheses that, in the regime of organic agriculture, a soil under different crop rotation systems can: i) substantially vary on the basis of SOC accumulation, soil metabolic activity and nutrient availability, and ii) differentiate soil conditions for the different adaptation and development of the plant-root system.…”