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

Shoji Hashimoto,Koh Hashida,Hiroyuki Tobita,Shin Ugawa,Mitsutoshi Kitao

doi:10.3389/ffgc.2021.768953

Abstract

In this study, we examined the composition of organic constituents of stem woody tissue together with tree growth in Quercus mongolica var. grosseserrata Blume seedlings raised under controlled CO2 and/or O3 concentrations in a Free-Air Concentration Enrichment system. After exposure to ambient air (control), elevated CO2 concentration (550 μmol mol–1 CO2), elevated O3 concentration (double that of the control), and a combination of elevated CO2 and O3 concentrations during a growing season, we measured the diameter and length of stem, and biomass of sampled seedlings and quantified the lignin, extractive, and holocellulose contents of the woody tissue of current-year stems. We confirmed that the growth of seedlings was enhanced under an elevated CO2 concentration condition. In line with this, the extractive content was lower in woody tissue formed under an elevated CO2 concentration than that formed under ambient air, whereas holocellulose content showed an inverse pattern. Elevated O3 concentration itself did not change the organic constituents of the woody tissue, but it reduced the influence of an elevated CO2 concentration. We thus assume that Q. mongolica formed woody tissue with a low extractive content under the high CO2 concentration condition, although this response was possibly mitigated by an elevated O3 concentration. Extractives contains antimicrobial components such as tannins, flavonoids, quinones, and terpenoids. The decrease in extractives within the widely distributed Q. mongolica in East Asia may have a non-negligible impact on C cycling in the future earth with high atmospheric CO2 concentration.

Highlights

Emissions of atmospheric carbon dioxide (CO2) and tropospheric ozone (O3) have been increasing because of anthropogenic activities (e.g., IPCC, 2013; Ainsworth et al, 2020; Takahashi et al, 2020)
Many studies have demonstrated that elevated CO2 concentrations enhance the rate of photosynthesis and the biomass growth of trees (e.g., Zak et al, 2011; Walker et al, 2019), photosynthetic downregulation has been observed with long-term exposure to elevated CO2 concentrations (e.g., Norby et al, 2010; Sigurdsson et al, 2013)
We evaluated the growth of seedlings and analyzed the organic constituents of the stem woody tissue of Q. mongolica seedlings grown over 180 days under controlled CO2 and/or O3 concentrations in Free-Air Concentration Enrichment (FACE) systems

Summary

Introduction

Emissions of atmospheric carbon dioxide (CO2) and tropospheric ozone (O3) have been increasing because of anthropogenic activities (e.g., IPCC, 2013; Ainsworth et al, 2020; Takahashi et al, 2020). Elevated atmospheric CO2 and O3 concentrations can influence forest productivity (Agathokleous et al, 2020; Ainsworth et al, 2020), and further impacts on carbon (C) cycling in forest ecosystems. Additional research has reported that leaf and leaf litter changes influence decomposition rates (e.g., Kasurinen et al, 2006, 2017; Parsons et al, 2008). This effect may be present in other tissues. Studying the organic composition of woody tissues formed under elevated CO2 and/or O3 concentrations provides important insight into understanding their impact on C cycling in forest ecosystems

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