Chemical and anatomical changes in Liquidambar styraciflua L. xylem after long term exposure to elevated CO₂

The anatomical and chemical characteristics of sweetgum were studied after 11 years of elevated CO₂ (544 ppm, ambient at 391 ppm) exposure. Anatomically, branch xylem cells were larger for elevated CO₂ trees, and the cell wall thickness was thinner. Chemically, elevated CO₂ exposure did not impact the structural components of the stem wood, but non-structural components were significantly affected. Principal component analysis (PCA) was employed to detect differences between the CO₂ treatments by considering numerous structural and chemical variables, as well as tree size, and data from previously published sources (i.e., root biomass, production and turnover). The PCA results indicated a clear separation between trees exposed to ambient and elevated CO₂ conditions. Correlation loadings plots of the PCA revealed that stem structural components, ash, Ca, Mg, total phenolics, root biomass, production and turnover were the major responses that contribute to the separation between the elevated and ambient CO₂ treated trees.