Assessing the Impact of Drought-Induced Abiotic Stress on the Content and Composition of Douglas-Fir Lignin

Drought is one of the most concerning stress factors for lignocellulosic biomass, decreasing productivity and altering its physical and chemical properties and, consequently, its value as a renewable feedstock. Accelerating climate change is expected to result in increasingly frequent and severe droughts, disproportionately impacting northern latitudes. This study investigates the impact of drought-induced abiotic stress on the composition of Douglas-fir (Pseudotsuga menziesii) wood, focusing on lignin content and composition. Klason lignin analysis, solid-state C-13 NMR, and Py-GC/MS all determine a similar to 4%-5% higher lignin content in the drought-stressed wood compared to the control. The chemometric modeling of Py-GC/MS data provides quantitative molecular indicators of an increased lignin content in wood due to drought stress. Moreover, quantitative 31P NMR results reveal evidence that drought stress may alter the composition of lignin in Douglas-fir wood. In particular, an increase in phenolic hydroxyl groups and a decrease in aliphatic hydroxyl groups indicate a more hydrophobic lignin, which could promote lignin-enzyme interactions and inhibit the enzymatic hydrolysis of biomass. These findings highlight important indicators of compositional changes in Douglas-fir wood as a biorefinery feedstock under shifting climates. Further investigation will be necessary to better understand lignin's role in the drought response of Douglas-fir for fundamental insights and practical selective breeding strategies.