Insights on Molecular Characteristics of Hydrochars by 13C-NMR and Off-Line TMAH-GC/MS and Assessment of Their Potential Use as Plant Growth Promoters

Abstract

Hydrochar is a carbon-based material that can be used as soil amendment. Since the physical-chemical properties of hydrochar are mainly assigned to process parameters, we aimed at evaluating the organic fraction of different hydrochars through 13C-NMR and off-line TMAH-GC/MS. Four hydrochars produced with sugarcane bagasse, vinasse and sulfuric or phosphoric acids were analyzed to elucidate the main molecular features. Germination and initial growth of maize seedlings were assessed using hydrochar water-soluble fraction to evaluate their potential use as growth promoters. The hydrochars prepared with phosphoric acid showed larger amounts of bioavailable lignin-derived structures. Although no differences were shown about the percentage of maize seeds germination, the hydrochar produced with phosphoric acid promoted a better seedling growth. For this sample, the greatest relative percentage of benzene derivatives and phenolic compounds were associated to hormone-like effects, responsible for stimulating shoot and root elongation. The reactions parameters proved to be determinant for the organic composition of hydrochar, exerting a strict influence on molecular features and plant growth response.

Multi-Parameter Characterization of Disease-Suppressive Bio-composts from Aromatic Plant Residues Evaluated for Garden Cress (Lepidium sativum L.) Cultivation

“…The relative preservation of apolar compounds during the dynamics of natural organic materials such as litter, soil organic matter, compost, digestates, etc. are in fact closely correlated with the advancement of carbon stabilization and the so-called humification process [29,34]. Bioactive properties are thus triggered by depolymerized organic molecules released by the intense humification process, mainly represented by aromatic and phenolic compounds and decomposed peptide moieties [48].…”

“…The A/OA and HB indices are mainly used as references to determine the biochemical stability of organic matrices and correlate the structural composition with the stabilization processes of organic materials [28,29]. The Lig R ratio is a useful indicator to discriminate between NMR signals due to lignin and other phenolic compounds (lower LigR) versus the prevalent contribution of peptidic moieties (larger LigR) in the 45-60 ppm range of the NMR spectra [17,30].…”

“…In addition to the monomers of the saccharide chains, the O-alkyl regions of the NMR spectra may also include a contribution from the carbohydrate moieties of the glycosidic components in the structures of the flavonoids of aromatic plants [31,37]. The reduced evidence of carbon 4 involved in the β 1→4 glycosidic bond at 82/88 ppm suggested the decomposition of the ether bond of the polysaccharides chain in composting processes, as well as the incorporation of mannan, xylan and arabinan derivatives into the hemicellulose structures of the initial fresh plant biomass [29,30].…”

Biochar extract compounds alter germination and growth of crop seed

“…However, the exact opposite effect on seedling growth and the pyrolysis temperature was observed by Kong et al (2021). Fregolente et al (2021) created hydrochar extracts via a phosphoric acid treatment and observed elevated bioavailable lignin-derived compounds. These compounds appeared to enhance corn seedling growth.…”

“…These authors contended that the antagonistic effect on seed vitality was likely due to the presence of bio-oil, i.e., aromatic compounds, in the biochar, creating biological toxicity. Oppositely, Fregolente et al (2021) found that the benzene derivatives and phenolic compounds, i.e., both aromatic compounds, present in the biochars were responsible for stimulating the shoot and root elongation.…”