Molecular Characterization of Extracts from Biorefinery Wastes and Evaluation of Their Plant Biostimulation

Biorefinery residues from non-food biomasses are promising sources of sustainable agrochemicals. The molecular properties of water-soluble extracts from ligno-cellulosic biomass pretreated first by steam-explosion and then by enzymatic hydrolyses at different buffer doses, were assayed for bioactivity on maize. C-13 and P-31 nuclear magnetic resonance (NMR) spectra showed that extracts varied in phenolic and carboxyl content, while high performance size exclusion chromatography and diffusion ordered spectroscopy NMR revealed that Ox-BYP 1 obtained from wastes treated with a greater buffer dose contained small-sized molecules associated in apparently large metastable aggregates. Ox-BYP 2 separated from wastes treated with smaller buffer concentrations showed a more stable conformation. Both hydrolysates revealed a positive dose-dependent bioactivity toward maize growth. Ox-BYP 1 promoted plant fresh and dry weights and root length at 10 and 100 ppm but decreased seedling growth at 1 ppm. Instead, Ox-BYP 2 increased the whole plant growth at all assayed concentrations. Their different biostimulation effects were attributed to the toxicity of easily bioaccessible lignin-derived phenolics at small concentrations of Ox-BYP 1, which was removed by molecular self assembly at greater concentrations. Conversely, the more strongly associated Ox-BYP 2 exerted a positive bioactivity even at small doses. The bioactivity of extracts from biorefinery wastes appeared to depend on molecular composition and, in turn, on waste pretreatments.