Effects of long-term elevated CO2 treatment on the inner and outer bark chemistry of sweetgum (Liquidambar styraciflua L.) trees

Abstract

Key message Long-term exposure of sweetgum trees to elevated atmospheric CO 2 concentrations significantly shifted inner bark (phloem) and outer bark (rhytidome) chemical compositions, having implications for both defense and nutrient cycling. Abstract Changes in plant tissue chemistry due to increasing atmospheric carbon dioxide (CO 2 ) concentrations have direct implications for tissue resistance to abiotic and biotic stress while living, and soil nutrient cycling when senesced as litter. Although the effects of elevated CO 2 concentrations on tree foliar chemistry are well documented, the effects on tree bark chemistry are largely unknown. The objective of this study was to determine the effects of a long-term elevated CO 2 treatment on the contents of individual elements, extractives, ash, lignin, and polysaccharide sugars of sweetgum (Liquidambar styraciflua L.) bark. Trees were harvested from sweetgum plots equipped with the Free-Air CO 2 Enrichment (FACE) apparatus, receiving either elevated or ambient CO 2 treatments over a 12-year period. Whole bark sections were partitioned into inner bark (phloem) and outer bark (rhytidome) samples before analysis. Principal component analysis, coupled with either Fourier transform infrared spectroscopy or pyrolysis-gas chromatography-mass spectrometry data, was also used to screen for differences. Elevated CO 2 reduced the N content (0.42 vs. 0.35 %) and increased the C:N ratio (109 vs. 136 %) of the outer bark. For the inner bark, elevated CO 2 increased the Mn content (470 vs. 815 mg kg -1 ), total extractives (13.0 vs. 15.6 %), and residual ash content (8.1 vs. 10.8 %) as compared to ambient CO 2 ; differences were also observed for some hemicellulosic sugars, but not lignin. Shifts in bark chemistry can affect the success of herbivores and pathogens in living trees, and as litter, bark can affect the biogeochemical cycling of nutrients within the forest floor. Results demonstrate that increasing atmospheric CO 2 concentrations have the potential to impact the chemistry of temperate, deciduous tree bark such as sweetgum.

Composition of Organic Carbon-Based Compounds in the Stem Wood of Quercus mongolica Seedlings Grown Under Elevated CO2 and/or O3 Concentrations

“…We separated the current-year stem, formed under treatments within the FACE system, from the other parts. The bark of the current-year stem was removed using a chisel to eliminate the influence of bark chemicals, which may be altered under elevated CO 2 concentrations (Eberhardt et al, 2015). The remaining portion of the stem (i.e., woody tissue) was ground into fine particles that could pass through a 4-mm-mesh screen.…”