Influence of Atmospheric and Climate Change on Tree Defence Chemicals
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Environmental factors associated with atmospheric and climate change can potentially modify the structure and function of the world’s forests. An important indirect effect of environmental variables such as elevated carbon dioxide (CO2), air temperature, ozone (O3), UV radiation, and water-related stress on forests results from the response of tree secondary metabolism. In particular, the concentrations of defence chemicals displayed by trees can change in response to certain climate change factors, and this may influence interactions with herbivores and pathogens, and the broader forest community. An evaluation of the literature relating to climate change effects on tree defence chemicals shows variable results in both direction and magnitude of concentration changes and a dearth of studies on chemicals other than carbon-based phenolics and terpenes. Nevertheless, some generalities are evident. Elevated CO2, O3, and UV-B tend to increase tree phenolics, while mono- and sesquiterpenes remain unchanged. Elevated temperature increases volatile terpene emissions and often foliar terpene concentrations, whereas phenolics are largely unaffected. Water stress tends to increase phenolic concentrations and mild stress can also increase terpene emissions, but the effect of excess water availability remains largely unknown. A greater understanding of the implications of global climate change factors on the defence chemistry of the world’s forest trees would benefit from increasing the classes of defence chemicals examined, expanding the diversity of tree species and biomes studied, and incorporating long-term, multi-factor experiments. Clearly much more work is required to fully understand how the complexity of factors involved in global climate change influence defence chemistry in the world’s forest trees, and how this in turn will influence future tree growth and fitness and forest ecosystem functioning.
KeywordsCondensed Tannin Phenolic Concentration Silver Birch Cyanogenic Glycoside Isoprene Emission
This work was supported by an Australian Research Council Discovery grant to JQDG & IEW (DP1094530).
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