Lignin and carbon transformation in roots of maize and mixed perennial biofuel crops
Perennial species are being explored as biofuel crops alternative to maize. In this study, fertilized and unfertilized mixed perennial prairie crops were compared with a conventional maize-soybean rotation and to continuous maize cropping systems to assess the potential production of above- and belowground lignin. The quantity and quality of lignin of aboveground and belowground samples as well as the cellulose and hemicellulose components of the biofuel crops were determined. In addition, a short-term incubation study was conducted to assess the impact of residue quality on root decomposition rate.
The acetyl bromide method was used to determine the total soluble lignin, and the alkaline CuO oxidation method was used to characterize lignin quality by the abundance of vanillyl, syringyl, and cinnamyl monomers. Cellulose and hemicellulose were extracted using acid hydrolysis and analyzed using high performance anion exchange chromatography-pulsed amperometry.
In general, there were no significant differences in aboveground lignin concentrations of the maize and mixed perennial crops. On the other hand, across all cropping systems, the belowground materials contained more lignin than the aboveground materials, and the lignin concentrations of maize roots were significantly greater than those of the roots of the perennial species. The composition of lignin residues in soil organic matter of the research plots appeared to be related to the quality parameters of root lignin (V, C, and S monomers). No systematic trends were observed in rank-correlation of root composition and root decomposition rates.