Effect of biochar on the metabolome of soybean seedlings

The use of biochar can have several effects on plant germination, depending on raw material, preparation method and application dose. However, the molecular mechanisms that lead to those results have yet to be elucidated. The aim of this research was to improve the understanding of these mechanisms by characterizing the metabolic effects of sugarcane bagasse biochar on soybean germination. Three types of biochars were prepared by pyrolysis at 300 ​°C (SCB300), 400 ​°C (SCB400) and 600 ​°C (SCB600). Then, each one was mixed into sand at 1%, 3%, 5% (w/w) dose, respectively. The experiment was performed in 8 days of incubation, when the number of germinated seeds and the average radicle length were determined. To evaluate the metabolome, the dry biomass (DB) was subjected to extraction with a mixture of methanol-d₄ and D₂O (1:1 v/v). The extracts were submitted to metabolomics analysis by Proton Nuclear Magnetic Resonance. The Relative Germination, Relative Average Radicle Growth and Germination Index increased in all treatments compared to control. On the other hand, the DB increased in all treatments, except for SCB300, at doses of 1% and 3% w/w. Seven metabolites (alanine, asparagine, acetic acid, citric acid, glycerol, fatty acids and sucrose) were identified and quantified in DB extracts as the most influential finding for the separation of treatments. Taken together, these results strongly suggested that biochars accelerated the catabolism of triacylglycerols to sucrose and induced a slight osmotic stress.