Figure 1.
Schematic overview of this study.
The effects of rice straw pretreatment on the cellulosic supramolecular structure and improvements in digestibility of lignocellulosic biomass for paddy soil microbiota were evaluated by physicochemical and biochemical methods. Rice straw samples were powdered using a blender, AM machine, and BM machine (1). Structural, compositional, thermodynamic, and degradability characterization (from 2–1 to 2–4) were performed using multimeasurement techniques such as FTIR, NMR, TG/DTA, and DGGE fingerprinting. Data were analyzed using the ECOMICS web-based toolkit.
Figure 2.
Structural characterization of biomass under different milling processes using FTIR spectroscopy.
FTIR spectrum of the FM-processed sample (A), PCA score plot (B), and loading plot (C) of biomass degradation profiles based on FTIR spectra. 1, anomeric vibration at the β-glycosidic linkage; 2, C–O stretching in cellulose and hemicellulose; 3, vibration of ester linkage; 4, aromatic skeletal and C–O stretching; 5, deformation vibrations of C–H bonds in benzene rings; 6, syringyl ring and C–O stretching in lignin and xylan; 7, C–H in cellulose and C1–O vibration in a syringyl derivative; 8, C–H deformation in cellulose and hemicellulose; 9, aromatic ring vibrations; 10, asymmetric C–H bonding in CH3 and –CH2–; 11, aromatic ring vibrations; 12, aromatic ring vibrations and C = O stretching; 13, stretching of C = O unconjugated to aromatic rings (oxidized side chains); 14, C–H stretching. Open square, FM-; closed triangle, AM1-; open triangle, AM2-; closed circle, BM1-; open circle, BM2-processed samples.
Figure 3.
Structural characterization of biomass under different milling processes using NMR spectroscopy.
13C CP-MAS and 13C-1H HETCOR NMR spectra of FM- (A), AM1- (B), AM2- (C), BM1- (D), and BM2-processed samples (E). The contact time was set to 1.0 ms for CP-MAS spectra. Characteristics of the biomass structure of each sample: PCA score plot (F) and loading plot (G) of 13C CP-MAS and digitized 1D 13C-1H HETCOR spectra. C1–C6, position of cellulose carbon; cry, crystalline cellulose; amr, amorphous cellulose; 1, CH3 in hemicellulose; 2, aliphatic –(CH2)n–; 3, OCH3 of lignin; 4, CH2OH of carbohydrates (C6 of amorphous cellulose); 5, CH2OH of carbohydrates (C6 of crystalline cellulose); 6 and 7, CHOH of carbohydrates (C2, C3, and C5 of cellulose); 8, CHOH of carbohydrates (C4 of amorphous cellulose); 9, CHOH of carbohydrates (C4 of crystalline cellulose); 10, OCHO of carbohydrates (C1 of cellulose).
Figure 4.
Compositional characterization of biomass under different milling processes using 1H-NMR spectroscopy.
PCA score plot (A) and loading plot (B) of biomass degradation profiles based on 1H-NMR spectra of high-molecular-weight extracted components. The loading plot refers to 1H-13C HSQC spectra (see Fig. 5). Open square, FM-; closed triangle, AM1-; open triangle, AM2-; closed circle, BM1-; open circle, BM2-processed samples; β-D-Xylp, β-D-xylopyranoside; α-L-Araf, α-L-arabinofuranoside; α-L-Fucp, α-L-fucopyranoside; G, guaiacyl; H, p-hydroxyphenyl; pCA, p-coumarate.
Figure 5.
Compositional characterization of biomass observed in 1H-13C HSQC spectra.
1H-13C HSQC spectra of BM1- (A) and BM2-processed samples (B), and their ratios (BM2/BM1) of peak intensity (C). *, not detected in BM1-processed samples; α-D-Glcp, α-D-glucopyranoside; β-D-Glcp, β-D-glucopyranoside; β-D-Xylp, β-D-xylopyranoside; α-L-Araf, α-L-arabinofuranoside; α-L-Fucp, α-L-fucopyranoside; 2-O-Ac-β-D-Xylp, acetylated β-D-Xylp; X1γ, γ-position of cinnamyl alcohol end group; S, syringyl; G, guaiacyl; H, p-hydroxyphenyl; pCA, p-coumarate.
Figure 6.
Thermodynamic characterization of biomass under different milling processes observed in TG/DTG analysis.
TG and DTG degradation curves (A) and bar graph of the activation energy required to decompose lignocellulosic components (B) in samples subjected to different milling processes. Dashed lines, TG profiles; solid lines, DTG profiles.
Figure 7.
Degradability characterization observed in NMR analysis.
Metabolic profiles of FM- (A, C) and BM2-processed samples (B, D) biomass samples evaluated using the PCA score plots (A, B) and loading plots (C, D) during biomass degradation by soil microbiota. Degraded biomass, including carbohydrates (*), in the BM2-processed sample is assigned from the 1H-13C HSQC NMR spectrum (E). The peaks indicated by numbers (listed in Table 1) were assigned as D-glucuronate, D-xylose, D-arabitol, cellobiose, and maltose.
Table 1.
Annotated peaks of BM2-processed samples extracted using a D2O solvent that were detected in 1H-13C HSQC spectra.
Table 2.
Taxonomic classification of the detected DGGE bands.