Additional file 1: Table S1. The total yield of solid fraction and dried liquid fraction after hydrothermal pretreatment. Table S2. Chemical compositions and recovery of the raw and pretreated substrates. Table S3. The reaction condition, treatment severity (log R0), XOS from the hydrothermal treatment of Chinese hickory shell. Table S4. Assignments of 13C-1H cross-signals in the HSQC spectra of the liquid fractions obtained from Chinese hickory shell during hydrothermal treatment. Figure S1. SEM images of raw and the pretreated substrates under (a) different pretreatment temperatures and (b) different times. Figure S2. X-ray diffraction of raw and the pretreated substrates under (a) different pretreatment temperatures and (b) different times. Figure S3. (a) Aliphatic region and (b) anomeric region in the 2D HSQC. Figure S4. (a) Aromatic region in the 2D HSQC NMR spectra of the dried liquid after hydrothermal pretreatment, (b) Main typical substructures in lignocellulose of the dried liquid after hydrothermal pretreatment.