Plant hydraulic characteristics such as turgor loss point and cell wall elasticity (in leaf tissues) and vulnerability to cavitation (in stem tissues) are often related to the lignin contents of these tissues. However, lignin content is also negatively related to decomposability of tissues. Currently, inefficiency of biochemical conversion of cellulosic biomass into biofuels is still a barrier for widespread biofuel production. In an effort to make cellulosic biofuel production more viable, an increasing number of potential biofuel plants are being engineered to have lower/altered lignin content. However, these changes may have unintended consequences for plant performance, particularly hydraulic function and the ability to withstand water stress. Using seven different reduced lignin genotypes of the perennial C4 grass, switchgrass (Panicum virgatum), we are investigating whether alteration of cell wall lignin content and composition negatively impact drought resistance characteristics (such as turgor loss point) and subsequent biomass production. We expect that switchgrass transgenics with reduced lignin will have greater sensitivity to drought due to thinner and therefore weaker secondary cell walls, and that greater sensitivity to drought will result in more dramatic reductions in stomatal conductance, photosynthesis, and biomass production under measured drought conditions.
Results/Conclusions
Results have been mixed so far, with lower turgor loss points in some low lignin genotypes, but also lower cell wall elasticity. Drought treatments have significantly reduced biomass production (up to 40%), especially aboveground, but biomass production has not been lower in low lignin mutants (p<0.05). As we test more genotypes, we can develop a more quantitative relationship between lignin content, xylem cell properties, and drought resistance. This research addresses fundamental questions in plant anatomy and physiology and can also contribute to improvement of an emerging biofuel crop.