Future Perspectives in Plant Biology Lignin and Biomass: A Negative Correlation for Wood Formation and Lignin Content in Trees

Studies in populations of forest tree hybrids have shown a negative correlation of biomass growth (usually measured as wood volume) and lignin content (Kirst et al., 2004; Novaes et al., 2009). The control of growth and lignin appears to be highly regulated, implying that selection for improved growth rate could effect a reduction in lignin content. Trees with increased biomass and reduced lignin would provide a yield advantage for pulp and paper production, as well as for production of biofuels. The purpose of this article is to briefly review the evidence for the correlation between lignin content and biomass growth and to discuss this correlation in a metabolic context. We review evidence that the regulation of the balance between lignin biosynthesis and biomass growth is mediated, at least in part, at the level of transcription, and expand previous results to show specific regulation within gene families of monolignol biosynthesis. Finally, we suggest a model of physiological control for the regulation of the relationship of wood formation and lignin content in trees. Wood, used by human societies for millennia, remains one of the world’s most abundant rawmaterials for industrial products and renewable energy. Wood is the secondary xylem of vascular plants, a tissue formed from the terminal differentiation of the inner side of the cambial meristem for vertical and horizontal transport of water, nutrients, and extractives. The secondary cell wall structure and composition of wood are the primary determinants of its physical and chemical properties, and of its energy content. Wood is typically composed of about 25% lignin, and 70% cellulosic carbohydrates, with roughly 45% cellulose and 25% hemicelluloses (Sjostrom, 1993). THE PROPERTIES OF LIGNIN IN WOOD