Pyrolysis carbon compound-specific isotope analysis (Py-CSIA) of Eucalyptus spp. bark and the extracted lignin

Abstract

Changes in climatic and environmental conditions can affect both, plant chemical molecular and atomic composition. Therefore, biomass carbon isotope composition is frequently used to gain information about the environmental conditions at the time a plant thrives. In this field, most studies use isotope values obtained from bulk samples. However, these values are a weighted average of the different plant compounds. The isotopic characterization of individual compounds represents a relevant analytical advance able to differentiate the isotopic composition of the main plant components i.e., polysaccharides, lignin, polypeptides, lipids, waxes, etc.Here, we investigate the link between molecular and isotope composition of bark and lignin extracted from three Eucalyptus species (E. grandis, E. dunnii and a hybrid E. grandis X E. dunnii) using pyrolysis compound-specific isotope analysis (Py-CSIA). This technique, although not widely used, has been previously developed and applied, with different variants, to characterize plant products including lignin, sugars, and terpenes. Retrieved results for both bark and lignin samples showed the isotopic differences regarding the diverse biogenic groups, accounting for a 13C-enrichment in polysaccharides up to 2.5‰ compared to lignin methoxyphenols, which is consistent with the fractionation during metabolization of the plant. A strong positive correlation was found between the bulk isotope and compound-specific values, especially when applying a weight factor related to the relative abundance of each compound, which support the analytical suitability of this technique. Despite that bark from different origins provide very similar pyrolysis patterns, isotopic composition of relevant specific compounds can make the difference giving additional valuable information.