Application of Raman spectroscopy to analyse lignin/cellulose ratio in Norway spruce tree rings

Abstract

Tree cores of Picea abies trees (>75 years old) from two different elevations (400 and 1100 m a.s.l.) in the Jeseníky Mountains were examined. Raman spectroscopy was used to analyse lignin/cellulose ratio in the latewood of individual tree rings from the last 35 years. The ratio was calculated based on the Raman intensity of the lignin band at ~1600 cm –1 assigned to phenyl groups and cellulose band at ~1096 cm –1 based on a vibration of glycosidic bonds. The results show a clear difference in lignin/cellulose ratios in trees from high and low elevations, while similar trends in lignin/cellulose ratios were found in tree cores originating from the same tree but different directions. Higher lignin/cellulose ratios were found at high elevation as compared to low elevation. The wood of spruces grown at high elevation also exhibited greater variability of lignin/cellulose ratios among individual tree rings as compared to trees from low elevation. A negative correlation between lignin/cellulose ratio and mean annual temperature was revealed. A weak positive correlation between lignin/cellulose ratio and total annual precipitation was also found. Redundancy analysis (RDA) showed a pronounced influence of precipitation in June. The results show great potential for Raman spectroscopy in tree-ring analysis.