Abstract

Research Highlights: Long-term exposure of paper birch to elevated carbon dioxide (CO2) and ozone (O3) modified metabolite content of over-wintering buds, but no evidence of reduced freezing tolerance was found. Background and Objectives: Atmospheric change may affect the metabolite composition of over-wintering buds and, in turn, impact growth onset and stress tolerance of perennial plant species in spring. Materials and Methods: Low molecular weight compounds of paper birch (Betula papyrifera) buds, including lipophilic, polar and phenolic compounds were analyzed, and freezing tolerance (FT) of the buds was determined prior to bud break after 11 growing seasons exposure of saplings to elevated concentrations of CO2 (target concentration 560 µL L−1) and O3 (target concentration 1.5 × ambient) at the Aspen FACE (Free-Air CO2 and O3 Enrichment) facility. Results: The contents of lipophilic and phenolic compounds (but not polar compounds) were affected by elevated CO2 and elevated O3 in an interactive manner. Elevated O3 reduced the content of lipids and increased that of phenolic compounds under ambient CO2 by reallocating carbon from biosynthesis of terpenoids to that of phenolic acids. In comparison, elevated CO2 had only a minor effect on lipophilic and polar compounds, but it increased the content of phenolic compounds under ambient O3 by increasing the content of phenolic acids, while the content of flavonols was reduced. Conclusions: Based on the freezing test and metabolite data, there was no evidence of altered FT in the over-wintering buds. The impacts of the alterations of bud metabolite contents on the growth and defense responses of birches during early growth in spring need to be uncovered in future experiments.

Highlights

  • The ongoing climate warming has caused the growing season to begin earlier in northern ecosystems [1,2]

  • 205 lipophilic compounds, 127 polar compounds and 25 phenolic compounds were quantified in the birch buds

  • Our results showed that both elevated CO2 (eCO2) (~560 ppm) and elevated O3 (eO3) (~1.5 × ambient) induced alterations in the chemical composition of paper birch buds

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Summary

Introduction

The ongoing climate warming has caused the growing season to begin earlier in northern ecosystems [1,2]. This may increase the exposure of vulnerable plant tissues, such as developing buds, to spring frosts [3,4]. Forests 2020, 11, 330 in the development of freezing tolerance (FT) include dehydration of cells, accumulation of proteins and carbohydrates, changes in hormone levels and increases in fatty acid desaturation in membrane lipids [5,6]. Healthy buds enable vigorous growth onset and high plant resistance to biotic and abiotic stress factors in spring

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