Fig 1.
Temporal variation of the residual mass percent of wheat straw.
Table 1.
Regression models of the wheat residual mass and incubation time.
Fig 2.
Temporal variation of the remaining C (a) and N (b) as a percentage of the original mass in decomposing wheat straw.
Table 2.
Regression models of carbon and nitrogen lost from wheat straw.
Fig 3.
Temporal variations in the remaining mass percentage (%) of cellulose, hemicellulose, and lignin in wheat straw residues under anaerobic (A) and aerobic (B) conditions.
Notes: Error bars indicate the standard deviation of the triplicate samples.
Fig 4.
13C multiCP NMR spectra (thin lines) and multiCP/DD NMR spectra (thick lines) of original and decomposing wheat straw at different incubation stages.
Fig 5.
Spectral editing for identification of functional groups in 3-month decomposing wheat straw under anaerobic (left) and aerobic (right) conditions: (a, b) nonselective cross polarization/total sideband suppression (CP/TOSS) spectra for reference, with a contact time of 1 ms at a spinning speed of 5 kHz; (c, d) corresponding dipolar dephasing CP/TOSS spectra showing nonprotonated carbons and mobile carbons, acquired after 40-μs of decoupling gated off; (e, f) selection of sp3-hybridized carbon signals by a 13C chemical shift anisotropy (CSA) filter with 35-μs filter time, other parameters as in (a); (g, h) corresponding selection of protonated sp3-hybridized C signals with a 35-μs CSA filter and short 50-μs CP; (i, j) selection of nonprotonated or mobile sp3-hybridized C signals with a 35-μs CSA filter and 40-μs dipolar dephasing; (k, l) selection of relatively immobile CH and CH2 signals with small residual CH3, which was achieved by finding the difference between a short-CP spectrum and a spectrum of short CP combined with dipolar dephasing.
All the spectra were normalized to the highest peak. Recycle delays for all the spectra were 1 s and the number of scans was 6144.
Table 3.
Temporal change of relative abundances of functional groups (%) in wheat straw obtained by multiCP NMR technique under anaerobic and aerobic conditions.
Fig 6.
Temporal change of alkyl/O-alkyl ratio of wheat straw under anaerobic and aerobic conditions during decomposition.
Alkyl refers to the multi CP NMR spectra region at 0–44 ppm, O-alkyl refers to the spectra region at 44–93 ppm.