How Can We Reduce Lignin Contents in Bioenergy Crop Production?.

In bioenergy production, lignin is not only hard to be converted into bio-ethanol but also makes negative impacts on conversion efficiency from biomass to bio-ethanol. In order to improve productivity of bioenergy production, lignin content in biomass needs to be effectively reduced. Lignin is a polymer in the cell walls of all plants. It is one of the most abundant natural polymers, constitutes one-fourth to one-third of the total dry weight of physiologically maturely plants. It is very meaningful to increase stiffness of plants and therefore, enhance their resistance to pests and diseases in the late growth stage of crop plants with reproductive organs such as panicles or fruits. Actually, grains or fruits are not necessarily needed in bioenergy production because biomass with little lignin may have greater potential of bio-ethanol production than grains or fruits. Additionally, expression of genes governing lignin biosynthesis is chronological and closely related to reproduction stage of crop plants. This trait provides two different opportunities for us to substantially reduce lignin contents in biomass for bioenergy production: choosing crops that would not initiate their reproductive growth if the requirements of their specific thermoperiod or photoperiod cannot be satisfied and harvesting bioenergy crops before they start biosynthesizing lignin greatly. Our recent research result shows lignin contents of the two tested wheat genotypes were very significantly different. 80-55 with satisfaction of its thermoperiod had significantly greater lignin content than YZ144 without satisfaction of its thermoperiod 8 weeks after seedlings emergence even though there was no significant difference in lignin contents between the two genotypes in the early growth stage. This preliminary result indicates that (i) lignin contents in bioenergy production can be genetically reduced; (ii) selection of bioenergy crop cultivars without satisfaction of thermoperiod can substantially reduce lignin contents; and (iii) harvest of bioenergy crops with satisfaction of thermoperiod before they greatly synthesize lignin can significantly decrease lignin contents in biomass.